JP6671631B2 - Optical sensor, optical inspection device, and optical characteristic detection method - Google Patents

Description

  The present invention relates to an optical sensor, an optical inspection device, and an optical characteristic detection method, and more particularly, to an irradiation system for irradiating a subject with light, and a detection system for irradiating light from the irradiation system and propagating in the subject. The present invention relates to an optical sensor including: an optical inspection device including the optical sensor; and an optical characteristic detecting method using the optical sensor.

  2. Description of the Related Art Conventionally, a living body optical measurement device that irradiates a subject (living body) with light and detects light that has propagated inside the subject has been known (for example, see Patent Document 1).

  In this biological optical measurement device, the pitch of a plurality of probes (probes) attached to a subject is reduced to obtain high resolution.

  However, in the biological optical measurement device disclosed in Patent Literature 1, the mountability to a subject is reduced.

The present invention provides an irradiation system including at least one light irradiator that irradiates a plurality of non-parallel lights to the same position of a subject, and a detection system that detects light emitted from the irradiation system and propagated in the subject. Wherein the light irradiator includes: a surface emitting laser array having a plurality of light emitting units; and a lens arranged on an optical path of a plurality of lights from the plurality of light emitting units; Ri light nonparallel der each other through the lens is emitted from at least two light emitting portion of the section, the plurality of light emitting portions each have a generally annular dielectric emission region, the at least two light emitting at least one light emitting portion of the part is an optical sensor in which the center of said dielectric is characterized that you have deviated from the center of the emission region.

  According to the present invention, it is possible to obtain high resolution without lowering the attachment to the subject.

It is a figure for explaining the schematic structure of the optical inspection device concerning a 1st embodiment of the present invention. It is a figure for explaining the water tank for phantoms. It is a figure for explaining the layout of a transparent window. FIG. 2 is a diagram (part 1) for describing a schematic configuration of the light source module according to the first embodiment. FIG. 3 is a diagram for explaining a schematic configuration of a detection module according to the first embodiment. FIG. 3 is a diagram (part 2) for describing a schematic configuration of the light source module according to the first embodiment. It is a figure for explaining a propagation angle in a living body. 5 is a flowchart for explaining a method for measuring information in a subject. It is a flowchart regarding an inverse problem estimation algorithm. FIG. 3 is a diagram (part 1) illustrating a sensitivity distribution in a photodiode (PD). FIG. 10 is a diagram (part 2) illustrating a sensitivity distribution in PD. It is a figure for explaining a propagation angle in a living body. FIG. 13A is a diagram illustrating the actual position of the light absorber, FIG. 13B is a diagram illustrating the estimation result of the position of the light absorber, and FIG. It is a figure showing a detection result of a position of a body. 14A is a diagram showing the actual position of the light absorber after the movement, and FIG. 14B is a diagram showing the estimation result of the position of the light absorber after the movement, and FIG. FIG. 7 is a diagram showing a detection result of a position of a light absorber in a comparative example. FIG. 9 is a diagram for explaining the arrangement of a plurality of light source modules and a plurality of detection modules in the optical sensor according to the second embodiment. FIG. 9 is a diagram for explaining a light source module LM according to a second embodiment. FIG. 9 is a diagram for describing a surface emitting laser array chip of a light source module LM according to a second embodiment. FIG. 9 is a diagram (part 1) for describing an additional configuration of the light source modules of the first and second embodiments. FIG. 9 is a diagram (part 2) for describing an additional configuration of the light source modules of the first and second embodiments. FIG. 11 is a diagram (part 3) for describing an additional configuration of the light source modules of the first and second embodiments. FIG. 3 is a ray diagram optically designed by an optical simulator. FIG. 6 is a diagram illustrating a result of an optical simulation according to the first embodiment. FIG. 9 is a diagram illustrating a result of an optical simulation in a comparative example. FIG. 9 is a diagram for describing a configuration of a surface emitting laser element in a surface emitting laser array chip according to a first modification of the second embodiment. FIGS. 25A and 25B are diagrams (part 1 and part 2) for explaining an inclined substrate, respectively. FIGS. 26A to 26D are diagrams (parts 1 to 4) for describing an offset distribution model 1 in the surface emitting laser array chip according to the first modification of the second embodiment. FIG. 14 is a diagram illustrating a relationship between a shift amount of the center of the annular dielectric from the center of the emission region and a tilt angle of the emission direction with respect to the Z axis in the first modification of the second embodiment. FIGS. 28A to 28D are diagrams (parts 1 to 4) for describing an offset distribution model 2 in the surface emitting laser array chip according to the second modification of the second embodiment. FIG. 14 is a diagram for explaining an offset distribution model 3 in a surface emitting laser array chip according to a modification 3 of the second embodiment. It is a figure for explaining an operation by a light source module of a comparative example. FIG. 14 is a diagram for explaining an operation of the light source modules of Modifications 1 to 3 of the second embodiment. FIG. 32A is a diagram for explaining the operation of the optical sensor of the comparative example, and FIG. 32B is a diagram for explaining the operation of the optical sensor of the first embodiment. 6 is a graph showing a relationship between an incident angle from air to a living body and a propagation angle in the living body. 5 is a graph showing a relationship between an incident angle from a resin to a living body and an in-vivo propagation angle. FIG. 11 is a diagram (part 1) for describing a schematic configuration of a detection module according to a second embodiment. FIG. 10 is a diagram (part 2) for describing a schematic configuration of the detection module according to the second embodiment. FIG. 11 is a diagram (part 3) for describing a schematic configuration of the detection module according to the second embodiment. 9 is a flowchart illustrating an optical characteristic detection method (position measurement method) according to a second embodiment. FIG. 14 is a diagram illustrating an estimation result of the inverse problem estimation in the second embodiment. FIG. 4 is a diagram for explaining the operation of the optical sensor according to the first embodiment. It is a flowchart for demonstrating the optical characteristic detection method (position measurement method) of 2nd Embodiment. It is a figure for explaining arrangement of a plurality of light source modules and a plurality of detection modules in an optical sensor of a 3rd embodiment. FIG. 8 is a diagram for explaining an emission direction of each light source module and a detection direction of each detection module in the optical sensor of the comparative example. FIG. 44A is a view for explaining the emission directions of four groups of the surface emitting laser array chip of the fourth embodiment, and FIG. 44B is a view for explaining four emission directions of the PD array of the fourth embodiment. FIG. 3 is a diagram for explaining a detection direction of a PD. It is a figure for explaining an outgoing direction of each light source module and a detection direction of each detection module in an optical sensor of a 4th embodiment. FIG. 3 is a block diagram illustrating a configuration of a control unit. FIG. 3 is a block diagram illustrating a configuration of a calculation unit.

<< 1st Embodiment >>
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a schematic configuration of an optical inspection apparatus 1000 according to the first embodiment.

  The optical inspection apparatus 1000 is used for diffuse optical tomography (DOT), for example. DOT is a technique for irradiating a subject (scattering body) such as a living body with light, detecting light propagated inside the subject, and estimating optical characteristics inside the subject. In particular, by detecting blood flow in the brain, it is expected to be used as a diagnostic aid for depressive symptoms and an assistive device for rehabilitation. In the DOT, when the resolution is improved, the function of the brain can be understood in detail. Therefore, many research institutes are actively conducting research for improving the resolution.

  As shown in FIG. 1, the optical inspection apparatus 1000 includes an optical sensor 10 including a light source module LM having a plurality of light emitting units and a detection module DM, a control unit, a display unit, a calculation unit, and the like. The control unit is configured as shown in the block diagram of FIG. In the control unit, the switch unit is controlled by the information from the central processing unit A-1, and the light emitting LM is selected. At this time, the current supplied to the LM via the switch is controlled to a desired value by the current controller. The detection result (data) in the DM is A / D converted, and an operation such as an averaging process is performed in the operation unit (A-2). The calculation results in the calculation unit (A-2) are sequentially recorded in the recording unit (A-3).

  In this specification, the light source module LM and the detection module DM are also referred to as probes when not distinguished. Further, in the present specification, the terms “simulated living body”, “living body”, and “subject” are used as appropriate, but the “simulated living body” and “living body” are still specific examples of the subject.

  The optical sensor 10 can be generally used as a sensor for detecting a light absorber in a subject, but a subject having the highest utility value is a living body. However, in general, it is not always easy to detect the position of a blood flow (light absorber) in a living body using an optical sensor, and it is difficult to confirm the effect (detection accuracy) of the optical sensor 10 when the subject is a living body.

  Therefore, in the present embodiment, a simulated living body (also referred to as a phantom) that is a cloudy liquid contained in an aquarium is used as a subject that has versatility and allows easy detection accuracy.

Hereinafter, Example 1 of the present embodiment will be described.
<Example 1>

In the first embodiment, a method is employed in which light beams from the respective light emitting units are deflected by a prism so that the angle of incidence on the subject differs between the light beams. Here, as shown in FIG. 2, transparent windows made of a transparent acrylic plate are provided at eight locations on one side wall (+ Z side wall) of a water tank in which each wall is formed of a black acrylic plate. The inside of the water tank is filled with an intrarapid aqueous solution (intrapid 10% concentration diluted 10-fold). That is, the simulated living body used in Example 1 is an aqueous intralipid solution.
Black ink is dripped into the intrarapid aqueous solution filled in this water tank so as to have a concentration of about 20 ppm, so that the absorption coefficient and the scattering coefficient are almost the same as those of a living body. Then, a black light absorber simulating the blood flow is submerged in the cloudy intrapid aqueous solution. The light absorber is a sphere having a diameter of about 5 mm as a black polyacetal. The sphere is fixed to a thin metal rod having a diameter of 1 mm connected to an automatic stage so that the position of the sphere can be controlled. A probe is accurately positioned and attached to each transparent window of the water tank.

  Here, the volume of the water tank is 140 mm × 140 mm × 60 mm. The thickness of the black acrylic plate is 4 mm. The eight transparent windows are composed of circular transparent windows A and B of two different sizes. There are four transparent windows A and B each. The diameter of the transparent window A is 9 mm, and the diameter of the transparent window B is 12 mm. The thickness of each of the transparent windows A and B is 1.5 mm.

  FIG. 3 shows a layout of eight transparent windows. The eight transparent windows are arranged in a grid at equal intervals in the X-axis direction and the Y-axis direction such that the transparent windows A and B are adjacent to each other. Here, the detection module DM is mounted on each transparent window A, and the light source module LM is mounted on each transparent window B (B1 to B4). The distance between the centers of two adjacent transparent windows is 30 mm.

  As shown in FIG. 4, the light source module LM includes a ceramic package (not shown) on which a lens, a prism, and a surface emitting laser array chip are mounted, and a flexible substrate (not shown) on which the ceramic package and an analog electronic circuit are mounted. , A wiring connected to the flexible board, a connector section (not shown), a housing in which these are accommodated, a window member made of a transparent resin that comes into contact with the subject, and the like. In the light source module LM, the light amount of the light emitting unit can be kept constant by controlling the current value to an appropriate value by a power supply unit (not shown). The light source module LM is mounted in a state where the window member is in contact with the subject (transparent window B) from the + Z side.

  As illustrated in FIG. 5, the detection module DM includes a black resin housing, a contact member made of an elastic body attached to a front end (−Z side end) of the housing, and a diameter housed in the housing. It is configured to include a 3 mm hemispherical lens (divided lens) and a 4-divided PD array (in which four photodiodes (PDs) are arranged in an array). An aperturer (opening) is formed at the tip of the housing and the contact member. The detection module DM is mounted in a state where the contact member is in contact with the subject (the transparent window A) from the + Z side. FIG. 5 illustrates only two of the four PDs (light receiving units).

  The split lens is arranged near the + Z side of the aperture. Therefore, the light emitted from the light source module LM to the subject and propagated in the subject enters the split lens via the aperture, and is refracted and emitted in a direction corresponding to the incident position and the incident direction on the split lens. (See FIG. 5).

  The four-divided PD array is arranged on the + Z side of the divided lens. Therefore, the light passing through the split lens enters one of the four light receiving sections (PD) of the 4-split PD array according to the traveling direction (the emission direction from the split lens). In this way, the detection module DM can classify the incident angles of the light incident from the subject into four angle ranges.

  The control unit detects the light reception amounts of the four PDs (light reception units) of the detection module DM attached to each transparent window A (light reception amounts of a total of 16 PDs), converts them into voltages by an operational amplifier, and records the voltages. Record in the department. Data is detected at a sampling rate of 1 msec, and the numerical values measured for 20 sec are averaged. In one measurement, data of 16 PDs is acquired.

  Next, the light source module LM will be described in detail. As a light source of the light source module LM, a 40-channel surface emitting laser array chip, that is, a surface emitting laser array chip having 40 VCSELs (surface emitting lasers) as light emitting units is employed.

  On the optical path of the light from the surface emitting laser array chip, a lens having a diameter of 3 mm, which makes the light substantially parallel light, is arranged (see FIG. 6). The distance between the light emitting surface (light emitting surface) of the surface emitting laser array chip and the principal point of the lens (optical center of the lens) is set to be equal to the focal length f (for example, 9 mm) of the lens. That is, the surface emitting laser array chip is arranged such that the emission surface is located at the focal position of the lens. The “focal length of the lens” is the distance between the principal point of the lens and the focal point.

  Here, 40 channels are turned on simultaneously, and the total output is about 50 mW. The parallel light emitted from the VCSEL is deflected by the prism as shown in FIG.

  As the prism, an acrylic prism having the same refractive index as that of the acrylic water tank is used. The reflecting surface of the prism is designed according to the diameter of the prism, and the angle of the reflecting surface is set so that light passing through the lens is incident on the acrylic water tank at an incident angle of about 50 °.

  The refractive index difference between the acrylic of the water tank and the prism and the phantom (intrapid aqueous solution) is set such that the propagation angle in the phantom is about 60 ° (θ1 in FIG. 6) according to Snell's law. The prism is attached to a rotation stage (not shown) that is rotatable around a rotation axis provided in the inner wall of the water tank and extending in the Z-axis direction.

  By rotating the rotary stage and the prism together, it becomes possible to change the incident angle and azimuth of light on the prism. Here, as shown in FIG. 7, measurement in four directions of + X, -X, + Y, and -Y is sequentially performed. That is, 4 × 4 16 measurements are performed in the four positions (B1 to B4) and four directions of the four light source modules LM. A space between the prism and the water tank is filled with a gel-like resin (not shown) having the same refractive index as these. Thereby, refraction and reflection between the prism and the water tank can be prevented.

  Next, a method for measuring information in the subject will be described with reference to the flowchart shown in FIG.

  First, a probe is set (step T1). The probe means the detection module DM and the light source module LM as described above. The probes to be set here are four detection modules DM and one light source module LM. The four detection modules DM are individually mounted on four transparent windows A having a diameter of 9 mm shown in FIG. One light source module LM is mounted on the transparent window B1 shown in FIG.

  Next, 40 channels (light emitting units) of the light source module LM are caused to emit light simultaneously (step T2). The current value is determined so that the emission intensity is about 50 mW in total. The light emission time is about 20 sec. During this time, the detection values of the PDs of the four detection modules DM are read (step T3), and data (detection values) at several points detected at 1 msec intervals are averaged. Then, the averaged detection value, that is, the average value of the detection values is stored in the recording unit (step T4).

  Here, the measurement is performed in four directions of + X direction, + Y direction, -X direction, and -Y direction (steps T5 and T6). Specifically, steps T2 to T4 immediately after step T1 are performed in a state where the prism is arranged in the + X direction. Next, the prism is rotated to the + Y direction (step T6). Steps T2 to T4 are performed in this state. Next, the prism is rotated to the -X direction (step T6). Steps T2 to T4 are performed in this state. Next, the prism is rotated to the -Y direction (step T6). Steps T2 to T4 are performed in this state.

  Next, the mounting position of the light source module LM is sequentially changed from the transparent window B1 to B2, B3, and B4, and the four azimuths are measured again (steps T7 and T8). Thereafter, the position of the light absorber is moved, and the measurement is again performed at the four directions and the four mounting positions of the light source module LM (steps T9 and T10).

  The stored data are the data with and without the light absorber, respectively, and the data without the light are represented by the following r (s, i, n) (i = 1, 2, 3,... M, n = 1, 2, 3,... K) ), R (0, i, n) (i = 1, 2, 3,... M, n = 1, 2, 3,... K). i is a number assigned to each detection module DM. n is a number assigned to each group. Next, each difference Δr (i, n) is calculated.

  Hereinafter, a method of calculating the position of the light absorber (optical characteristics of the simulated living body) from the measurement result obtained by the above measurement method based on the flowchart of FIG. 8 will be described. Here, an inverse problem estimation algorithm is used. When solving the inverse problem, measurement and simulation are first performed, and a sensitivity distribution is created by the forward problem. Then, the data subjected to the next measurement is taken in, and the inverse problem is estimated from the value (see steps S21 to S25 in FIG. 9). FIG. 47 shows a block diagram of the calculation unit. Information such as the position of each module (probe), the refractive index, and the shape of the living body used in the Monte Carlo simulation is recorded in the recording unit (B-1). Based on this information, the previous order problem is performed. For this calculation, a GPU (multi-graphics processor) capable of performing parallel calculations is used. With this use, the calculation can be performed significantly faster than the conventional calculation speed. The sensitivity distribution obtained by the calculation is stored again in the recording unit (B-1). The calculation result and the measurement result stored in the recording unit (A-3) are input to the central processing unit (B-3), and the central processing unit (B-3) performs inverse problem estimation. The estimation result is displayed on the display unit via the central processing unit (A-1) (see FIG. 46).

  By the way, conventionally, it has been considered that light is scattered almost isotropically in a scatterer such as a living body when calculating the forward problem. For this reason, a simulation using a diffusion equation requiring a small amount of calculation has been used. However, recent academic societies and the like also report that light propagation in a living body has anisotropy in a fine area of mm unit. In order to perform a simulation reflecting this anisotropy, it is necessary to use a transport equation or perform a Monte Carlo simulation.

  In the present embodiment, the light emitted from the light source is deflected and made incident on the subject, so that information on the angle of incidence cannot be reflected in the diffusion equation that is generally used. Although a method using the transport equation has been proposed, it is known that this calculation takes an enormous amount of time.

  Therefore, in the present embodiment, Monte Carlo simulation is adopted. The Monte Carlo simulation is a technique for stochastically expressing the conditions under which photons scatter in a scattering medium using random variables, and observing their macroscopic behavior. Specifically, modeling is performed such that each time a photon moves through the medium and travels a certain distance, it collides and changes the directionality due to the collision. The average value of a certain distance at this time is the mean free path, defined by the scattering coefficient, and the change in direction is defined by the anisotropy g. This collision is repeated, and how it propagates in the defined area is recorded. By calculating innumerably the photons modeled in this way, the behavior of light in the scattering medium can be simulated. The route in which one photon diffuses is recorded by Monte Carlo simulation.

The Monte Carlo simulation in the present embodiment, the number of photons is 10 ^9, the voxels as 1mm cubes, the calculation of three-dimensional area of 120mm × 120mm × 60mm. Here, the scattering coefficient of the scattering medium, the absorption coefficient, anisotropy, ^{7.8 mm} -1 refractive index respectively is almost equal numbers and the ^scalp, 0.019 mm -1, and 0.89,1.37. The above-mentioned phantom (intralipid aqueous solution) is prepared so as to match this numerical value, and the light source module LM, the propagation angle, the position of the detection module DM, and the like are all simulated in the same situation as the phantom, and the sensitivity distribution is calculated.

At this time, regarding the position r of the voxel, the number of passed photons is defined as φ ₀ (r). In particular, when the position of the light source module LM is rs, the number of photons passed at the position r of the voxel is φ ₀ (rs, r). Next, the light source module LM is arranged at the position where the detection module DM is arranged, and the same number of photons is calculated again. If the detection module DM is installed at rd, the number of photons passed at the position r of the voxel is φ ₀ (r, rd).

Since the light path is reversible, this product is proportional to the number of photons that pass through the voxel position r, exit the light source module LM, and enter the detection module DM. The product obtained by normalizing this product with the number of photons φ ₀ (rs, rd) entering the detection module DM is the following sensitivity distribution A (r).

  The sensitivity distribution A (r) indicates the degree of influence on the detection amount at the position r. When a light absorber is generated at the position r of the voxel, the extent to which the detected value changes due to the generation is shown.

  An example of the sensitivity distribution calculated as described above is shown in FIG. Here, the light source module LM and the detection module DM are arranged at (X, Y, Z) = (45, 60, 0) and (X, Y, Z) = (75, 60, 0), respectively. Since the voxel is a cube of 1 mm, it is equivalent to the unit mm of these numerical values. The sensitivity of the voxel at each position is indicated by a logarithm (common logarithm) with the base being 10.

  Next, FIG. 11 shows the result of extracting a line of Y = 60 and Z = 10 from the voxel (x, y, z) from FIG. 10 and plotting the sensitivity as the vertical axis and the horizontal axis as the x position. ing. At this time, FIG. 12 shows the results of the case where the angle of propagation with respect to the X axis on the plane with the Y axis as the normal is + 60 ° and the case where the angle of propagation is −60 °.

  As shown in FIG. 11, there is a difference in sensitivity distribution between +60 degrees and −60 degrees. This difference is a guide to whether the resolution can be improved. In other words, the difference in the sensitivity distribution indicates that the propagation paths of the light from the two light sources are different. If the propagation path is the same, the sensitivity distribution should be almost the same even if the propagation angle is changed. Since the propagation paths of the light from the two light sources are different, the light from the two light sources collects different information.

  This creates great value for the inverse problem estimation described below. As described above, the light propagation is not simple isotropic scattering but has a slight anisotropy in the order of several mm. It is considered that the difference on the order of several mm is a factor for realizing the inverse problem estimation having a resolution on the order of several mm. This sensitivity distribution is implemented for all the light source module LM / detection module DM pairs implemented in the phantom under all propagation angle / detection angle conditions.

  Next, the inverse problem is estimated using this sensitivity distribution.

Assuming that the change δμ _a (r) of the absorption coefficient caused by the presence of the light absorber is sufficiently small, the following equation is established by approximating Retov.

ν is the speed of light in the medium, S is the amount of light emitted from the light source module LM per unit time, rs is the position of the light source module LM, rd is the position of the detection module DM, and φ (rs, rd) is the light source module represents the quantity of light emitted from the LM reaches the detection module DM, phi ₀ represents the intensity of light in the absence of light absorbing material. This equation means that given the light intensity φ _{0 in} the absence of the light absorber, the change in absorption coefficient δμ _a (r) caused by the presence of the light absorber and the observed value log φ (rs, rd) ) Can be linked to a linear relationship.

This can be simply described as follows.
Y = A (r) X

Here, Y is a change in the observed value depending on the presence or absence of the light absorber, and X indicates a change in the absorption coefficient at the position r of the voxel. A (r) is a sensitivity distribution. In the above equation, it is understood how the observed value Y changes by giving a change in the position or amount of the light absorber expressed by X.
In the inverse problem estimation, the reverse is performed, that is, the position X of the light absorber is estimated using the observed value Y. As described in the position measurement method above, the change due to the presence or absence of the light absorber is measured as Δr (i, n). This Δr (i, n) becomes the observed value Y, and X is calculated from this.

In general, an inverse problem estimation method called L2 norm regularization is used. In this method, X that minimizes a cost function C described below is calculated.

  Here, Y is an observed value, A is a sensitivity distribution, and λ is a regularization coefficient. Such a method is generally used in inverse problem estimation, but in the present embodiment, inverse problem estimation is performed by Bayes estimation that can also detect the depth direction. For the inverse problem estimation based on this Bayesian estimation, see the following non-patent documents: T. Shimokawa, T. Kosaka, O. Yamashita, N. Hiroe, T. Amita, Y. Inoue, and M. Sato, "Hierarchical Bayesian estimation improves depth accuracy and spatial resolution of diffuse optical tomography, "Opt. Express * 20 *, 20427-20446 (2012).

  As a result, an estimation result as shown in FIG. 13B can be derived. FIG. 13A shows the position of the light absorber. The grid in FIG. 13B was 3 mm, and it was found that it coincided with the actual position with an accuracy of 3 mm.

  As a comparative example, FIG. 13C shows a result of detection using only one of the four directions. This comparative example has substantially the same configuration as the conventional NIRS (DOT) device. In the comparative example, detection in the depth direction is impossible, and the detection result is very wide. In the first embodiment, the position and depth of the light absorber can be detected by the Bayes estimation.

  FIG. 14B shows the result of estimation (estimated result) by changing the position of the light absorber (see FIG. 14A). Also in this case, it can be seen that the actual position of the light absorber can be accurately estimated. According to the method of the first embodiment, the position of the light absorber can be detected with high resolution. On the other hand, in the comparative example, as shown in FIG. 14C, the light-absorbing body is considerably widened, and the position of the light-absorbing body cannot be accurately detected.

  Hereinafter, Example 2 of the present embodiment will be described. In the description of the second embodiment, a description related to the first embodiment will be made as appropriate.

<< Example 2 >>
First, black ink is dropped to about 200 ppm to an intrarapid aqueous solution (intrapid 10% concentration diluted 10 times) injected into a transparent acrylic water tank, and the absorption coefficient and the absorption coefficient are substantially the same as those of a living body. The scattering coefficient is used. A black light absorber simulating the blood flow is submerged in the cloudy intrapid aqueous solution. The light absorber is, for example, a polyacetal sphere having a diameter of about 5 mm in black. The sphere is fixed to a thin metal rod having a diameter of 1 mm connected to an automatic stage so that the position of the sphere can be controlled. The side of the water tank and the position of a probe described later are accurately determined and installed (mounted). Here, the acrylic water tank is, for example, a rectangular parallelepiped water tank having a volume of 140 mm × 140 mm × 60 mm and a wall thickness of 1 mm.

  The optical sensor 10 includes an irradiation system including a plurality (for example, eight) of light source modules LM, and a detection system including a plurality (for example, eight) of detection modules DM. The plurality of light source modules LM and the plurality of detection modules DM are respectively connected to the control unit via electric wiring.

  The control unit controls the light emission timing of the light source in each light source module LM and the detection timing in each detection module DM, and transfers the obtained detection result to the recording unit. Further, the control unit reads data recorded in the recording unit, performs a calculation using the numerical value, and controls to display the calculation result on the display unit.

  As illustrated in FIG. 15, the eight light source modules LM and the eight detection modules DM each include, for example, a light source module LM with respect to a simulated living body (not shown) in both the X direction and the Y direction orthogonal to each other. The detection modules DM are arranged in a matrix (two-dimensional lattice) at equal pitches a in the X and Y directions so as to be adjacent to each other. In FIG. 15, LM is indicated by a square, and DM is indicated by a circle.

  As shown in FIG. 16, the light source module LM includes, for example, optical elements such as lenses and prisms, a ceramic package (not shown) on which a plurality of surface emitting laser array chips are mounted, and the ceramic package and analog electronic circuits are mounted. A flexible board (not shown), wiring connected to the flexible board, a connector section (not shown), a housing in which these are accommodated, a window member made of a transparent resin that comes into contact with a subject, and the like.

  The oscillation wavelength of each surface emitting laser (VCSEL) of the surface emitting laser array chip is, for example, 780 nm or 900 nm. This wavelength is selected because the absorption coefficient varies greatly depending on the oxygen concentration in the blood. In the light source module LM, as shown in FIG. 16, a surface emitting laser array chip 1 having an oscillation wavelength of 900 nm and a surface emitting laser array chip 2 having an oscillation wavelength of 780 nm are arranged in parallel. The lens 1 is arranged near the end, and the lens 2 is arranged near the emission end of the surface emitting laser array chip 2. Each surface emitting laser is also called a ch (channel).

  The light from each surface emitting laser array chip is refracted by a corresponding lens, deflected (reflected) by a prism as a reflecting member formed inside the window member, and emitted out of the housing.

  As shown in FIG. 17, the surface emitting laser array chip has a square shape with a side of about 1 mm, and includes a plurality of (for example, 20) surface emitting lasers two-dimensionally arranged.

  More specifically, each surface emitting laser array chip has five groups (ch groups) each including four surface emitting lasers. Here, the centers of four of the five groups are individually located at the four vertices of the square, and the center of the other group is located at the center of the square.

  The four channels of each group are mounted on the ceramic package as described above, and are connected to the same electrode pad (one of the electrode pads 1 to 4) via a bonding wire (wiring).

  The ceramic package is mounted on the wiring pattern of the flexible board by soldering. A semiconductor for switching and a semiconductor for current stabilization are arranged on the flexible substrate. The switching semiconductor controls which channel of the surface emitting laser array chip emits light. The switching semiconductor causes the selected channel to emit light in response to an external serial signal. One end of the signal line for the serial signal and one end of the power supply line are connected to a flexible board, and the other end of the signal line and the other end of the power supply line are connected to a control unit.

  The light emission amount of each channel is set to be constant by calibration performed at regular intervals. In a normal use method, light emission of five groups is sequentially emitted in short pulses. Such pulse emission avoids a temperature rise due to heat generation, and is suitable for stabilizing the amount of emitted light. By integrating and averaging the detection values obtained by the detection module obtained each time a short pulse is emitted, noise-resistant detection is achieved.

  Hereinafter, the reason why the surface emitting laser array chip is adopted as the light source of the optical sensor 10 will be described. In the surface emitting laser array chip, a plurality of channels can be two-dimensionally arranged at close positions, and the light emission of each channel can be controlled independently. By installing a small lens near the channel, the traveling direction of the emitted light can be changed.

  Further, in an optical sensor used for DOT, it is required to control an incident angle to a subject as accurately as possible. Since a general LED (light-emitting diode) has a wide radiation angle, it is necessary to make the lens aspherical in order to make parallel light with high accuracy. In addition, a general LD (edge-emitting laser) has an asymmetric radiation angle, and in order to produce high-precision parallel light with a lens, it is necessary to combine two lenses or cylindrical lenses having different vertical and horizontal curvatures. However, the configuration becomes complicated, and a high-precision mounting is required.

  On the other hand, the surface emitting laser has an almost perfect circular far-field pattern, and one spherical lens may be arranged to generate parallel light. When coherent light emitted from an LD is used, speckles in which scattered lights interfere with each other occur in a subject (scatterer). This speckle pattern adversely affects measurement as noise.

  When the blood flow in the brain is observed as in the case of DOT, the number of scattering times is very large, so that there is no significant effect. However, there is an effect of the return light in which the light reflected on the skin surface returns directly to the light source. The return light destabilizes the oscillation state inside the LD, so that stable operation cannot be performed. When stably using coherent light in an optical disc or the like, a wavelength plate or the like is used so that specularly reflected light does not become return light. However, it is difficult to remove the reflected light from the scatterer.

  In the case of a surface emitting laser array chip, it is possible to irradiate a small area with a plurality of lights at the same time, and to reduce the return light interference (see, for example, JP-A-2012-127937).

  In the present embodiment (Examples 1 and 2), a convex lens (also simply referred to as “lens”) is arranged on the optical path of light from the surface emitting laser array chip (see FIG. 18).

  The diameter of this convex lens is 1 mm, and the effective diameter ε of the convex lens is 600 μm. The focal length f of the convex lens is 600 μm. The surface emitting laser array chip is a 1 mm square chip, and the center-to-center distance dmax between the two furthest channels in the surface emitting laser array chip is 600 μm. Thus, by making dmax and ε coincide with each other, the diameter of the convex lens can be minimized.

  Here, the convex lens and the surface emitting laser array chip have a distance L in the optical axis direction of the convex lens between the principal point (optical center) of the convex lens and the light emitting surface (emission surface) of the surface emitting laser array chip. It is positioned so as to be 300 μm. That is, f ≠ L.

  In this case, it is possible to avoid a phenomenon that the light emitted from the surface emitting laser array chip and transmitted through the convex lens is specularly reflected by a prism or the like and is condensed on the surface emitting laser array chip by the convex lens (return light phenomenon). it can. As described above, since no return light is generated, it is possible to stabilize the light emission amount of each channel of the surface emitting laser array chip. However, when the influence of the return light is not considered (when high resolution is not required for NIRS), f = L may be set.

  Further, as shown in FIG. 19, the space between the convex lens and the surface emitting laser array chip is filled with a transparent resin so that no air layer is interposed. As the transparent resin, a resin having a refractive index equivalent to that of a convex lens (for example, a thermosetting epoxy resin) is used. That is, the refractive index does not change at each interface between the convex lens and the surface emitting laser array chip. The transparent resin may be molded with a mold before fixing the convex lens, or may be injected after fixing the convex lens.

  By filling the space between the convex lens and the surface emitting laser array chip with the transparent resin, light emitted from the surface emitting laser array chip is reflected on the surface of the convex lens on the surface emitting laser array chip side. That is, generation of return light can be prevented. Since no return light is generated, the amount of light emitted from each channel can be stabilized. If the light quantity of each channel becomes stable, the S / N (signal / noise) ratio of the measurement system becomes good, and highly accurate NIRS measurement and high resolution can be realized.

  As shown in FIG. 20, the convex lens is fixed via a submount to a package on which the surface emitting laser array chip is mounted. In the surface emitting laser array chip, an electrode on the chip (chip electrode) is electrically connected to a PKG electrode on a package by a wire. Since the wire has a height of about several tens of micrometers, it is designed so as not to interfere with the submount. The fixing position L of the convex lens (the distance between the light emitting surface of the surface emitting laser array chip and the principal point of the convex lens) is restricted by the height of the wire. That is, in the case of using a wire, it is necessary to adopt a structure that avoids a submount or to set the height of the wire to 100 μm or less. That is, it is preferable that -100 um <fL <0 holds. However, in FIG. 20, the illustration of the transparent resin shown in FIG. 19 is omitted.

  The light emitted from the emission surface of the surface emitting laser is substantially circular, and its divergence angle is about 5 degrees in half width. Since a general LD beam has an elliptical shape, it is necessary to consider a setting error in the rotation direction. However, a surface emitting laser has an advantage of not having to consider it. In addition, since the shape is circular, there is a merit that approximation using symmetry can be easily performed in an optical simulation used for solving an inverse problem.

  The beam emitted from the surface emitting laser is refracted by a convex lens arranged in the vicinity. The refraction angle is determined by the relative position between the surface emitting laser and the lens center (optical axis of the lens). Therefore, a desired refraction angle can be obtained by appropriately setting the position of each group and the position of the lens of the surface emitting laser array chip.

  In the second embodiment, the relative position between the channel and the optical axis of the convex lens is set such that the refraction angle is about 20 degrees. In the surface-emitting laser array chip, each channel can independently control light emission. Therefore, by selecting a channel to emit light, the direction of light emitted from the light source module LM can be changed.

  FIG. 21 shows an example of a ray diagram optically designed by the optical simulator. Here, three channels (light sources) imitating a surface emitting laser array chip and a lens having a diameter of 1 mm and f = 600 μm are arranged in the vicinity of the three channels. One of the three channels is arranged on the optical axis of the lens, and the other two channels are individually arranged on one side and the other side of the optical axis of the lens. Light from channels other than the channel on the optical axis is refracted by the lens, and the propagation direction (path) is bent. That is, two lights from two channels other than the channel on the optical axis are emitted in directions opposite to each other with respect to the optical axis of the lens at an angle of about 20 degrees with respect to the optical axis.

  Here, the light source module LM is designed such that the incident angle of light on the subject is about 55 degrees. Specifically, as shown in FIG. 16, the light source module LM individually deflects a plurality of lights emitted from the convex lens in a direction inclined about 20 degrees with respect to the optical axis thereof by a plurality of prisms. Thus, the angle of each of the plurality of lights with respect to the optical axis of the lens is changed from about 20 degrees to about 55 degrees, and the light is designed to be incident on the surface of the subject.

  The prism may be any as long as it reflects light. For example, a glass substrate on which a metal film is formed may be used. Further, for example, a prism utilizing a total reflection phenomenon caused by a difference in refractive index may be employed. As an example, FIG. 22 shows a result of an optical simulation. The light beam emitted from the VCSEL is refracted by the convex lens and then enters the prism.

  Here, the material of the prism is BK7, but a general optical material may be used. Light incident on the prism is totally reflected on the side surface (reflection surface) of the prism, and is incident on the subject at an incident angle of about 55 °. That is, the light passing through the convex lens is deflected by the prism so that the incident angle of the light on the subject becomes about 55 °. At this time, a transparent gel is interposed between the prism and the subject in order to prevent light scattering at the interface between the prism and the subject. Also in this case, a plurality of lights from the surface emitting laser array chip are converted into a plurality of non-parallel lights by a convex lens, reflected by a prism, and incident on a subject. As a result, a plurality of non-parallel substantially parallel lights are incident on the same position of the subject (see FIG. 22).

  The angle of propagation of the light beam within the subject changes from about 55 ° to about 60 ° due to Snell's law due to the refractive index difference between the prism and the subject.

  In an optical system including a convex lens and a prism, the propagation angle of light in a subject can be set by utilizing the fact that the positions of respective channels of a surface emitting laser array chip are different from each other. Here, by shifting the center of each channel (VCSEL) from the optical axis of the convex lens by approximately 200 μm, the propagation angle of the light emitted from each channel in the subject can be set to approximately 60 °. At this time, the plurality of lights emitted from the plurality of channels are emitted as a plurality of non-parallel substantially parallel lights from a plurality of different positions on the emission surface of the convex lens.

  FIG. 23 shows, as a comparative example, the result of an optical simulation when the fixed position is L = 1.6 mm with respect to the focal length of the lens f = 600 μm. When the difference between L and f is 1 mm or more, the beam spreads greatly as shown in FIG. When the beam spreads in this way, it is necessary to enlarge the incident surface of the subject. However, the practical size of the NIRS is limited to about φ2 mm. The limitation is that the distance between human hair roots is about 2 mm, and if the area is larger than this, optically, the hair becomes an obstacle and high resolution NIRS cannot be realized. That is, the difference between f and L is desirably less than 1 mm.

  The lenses 1 and 2 shown in FIG. 16 are directly fixed to a ceramic package on which a surface emitting laser array chip is mounted so as to be accurately and stably arranged at a designed position.

  In FIG. 21, the convex surface of the lens is directed to the surface-emitting laser side, but the reverse is also possible. As shown in FIG. 21, the distance between the surface emitting laser chip and the lens can be increased by arranging the lens such that the convex surface of the lens faces the surface emitting laser and the planar portion of the lens faces the subject. it can. In the chip mounting process, it is preferable that the allowable distance is long to some extent in order to prevent interference between arms for picking up components and components during mounting.

  The lens may be any optical component that refracts light, and a lens such as a GRIN (Gradient Index) lens using a refractive index distribution of an optical fiber may be used. The use of a GRIN lens has the advantage that, in comparison with the use of a spherical lens, a lens having generally small spherical aberration, low cost, and a small f-number can be selected.

  In the second embodiment, it is preferable that the spherical aberration is small in order to make the light incident on the edge of the lens rather than the center of the lens.

  As can be understood from the above description, a plurality of non-parallel lights are emitted from the light source module LM (see FIGS. 16 and 22).

  Then, a plurality of non-parallel lights from the light source module LM are incident on the same position of the subject (see FIGS. 16 and 22).

  This “same position” means, for example, when the light source modules LM are arranged at intervals of about 60 mm, the same position with respect to the 60 mm, and a plurality of positions separated by several mm from each other is also called the same position. I don't mind. In other words, “identical” at “identical position” is not the same in a strict sense, but may be rephrased as “substantially identical” or “substantially identical”.

  An algorithm for solving the inverse problem will be described later. At that time, an optical simulation in which the position of the light source module LM is set is performed. When the optical simulation is performed, by accurately setting the shift of the incident position on the subject, no error occurs in estimating the inverse problem. The same applies to a surface emitting laser array chip having a plurality of channels having different oscillation wavelengths. Even if the incident positions of a plurality of lights from a plurality of channels having different oscillation wavelengths are shifted by several mm, the plurality of light beams The incident positions may be said to be the same position.

  On the other hand, when the distance between the probes is reduced and the probes are arranged at a high density, the light irradiation area on the subject by the plurality of light source modules LM (probes for light irradiation) is close to each other. It is desirable that the deviation of the incident position on the specimen be small. That is, it is desirable to further increase the identity of the “identical position”.

  Therefore, the present inventors have made the emission directions of the plurality of light emitting units of the surface emitting laser array chip non-parallel to reduce the shift of the incident position of the plurality of lights from the light source module LM to the subject. I found it. The method will be specifically described below.

  FIG. 24 shows an XZ cross-sectional view of a surface emitting laser element constituting each light emitting unit of the surface emitting laser array chip of the light source module LM of the first modification of the second embodiment. Hereinafter, the laser oscillation direction will be described as the Z-axis direction, and two directions orthogonal to each other in a plane perpendicular to the Z-axis direction will be described as the X-axis direction and the Y-axis direction.

  The surface emitting laser device 100 is, for example, a surface emitting laser device having an oscillation wavelength of 780 nm band, and includes a substrate 101, a buffer layer 102, a lower semiconductor DBR 103, a lower spacer layer 104, an active layer 105, an upper spacer layer 106, and an upper semiconductor. It has a DBR 107, a contact layer 109, and the like.

  The surface of the substrate 101 is a mirror-polished surface, and as shown in FIG. 25A, the normal direction of the mirror-polished surface (principal surface) is different from the crystal orientation [100] direction in the crystal orientation. [11 1] An n-GaAs single crystal substrate inclined at 15 degrees (θ = 15 degrees) in the A direction. That is, the substrate 101 is a so-called inclined substrate. Here, as shown in FIG. 25B, the crystal orientations are arranged such that the [0-11] direction is the + X direction and the [01-1] direction is the -X direction.

  Here, it is assumed that the use of an inclined substrate as the substrate 101 provides a polarization control effect for stabilizing the polarization direction in the X-axis direction.

  The buffer layer 102 is laminated on the + Z side surface of the substrate 101 and is a layer made of n-GaAs.

The lower semiconductor DBR 103 is stacked on the surface on the + Z side of the buffer layer 102, and includes a low refractive index layer made of n-Al _0.93 Ga _0.07 As and n-Al _0.3 Ga _0.7 As. It has 42.5 pairs of high refractive index layers. Between each of the refractive index layers, a composition gradient layer having a thickness of 20 nm in which the composition is gradually changed from one composition to the other composition is provided in order to reduce the electric resistance. Each refractive index layer is set to have an optical thickness of λ / 4, where λ is the oscillation wavelength, including １ ／ of the adjacent composition gradient layer. When the optical thickness is λ / 4, the actual thickness D of the layer is D = λ / 4n (where n is the refractive index of the medium of the layer).

The lower spacer layer 104 is stacked on the + Z side of the lower semiconductor DBR 103 and is a layer made of non-doped Al _0.33 Ga _0.67 As.

The active layer 105 is stacked on the + Z side of the lower spacer layer 104 and is a triple quantum well structure active layer made of GaInAsP / Al _0.33 Ga _0.67 As.

The upper spacer layer 106 is stacked on the + Z side of the active layer 105 and is a layer made of non-doped Al _0.33 Ga _0.67 As.

  A portion composed of the lower spacer layer 104, the active layer 105, and the upper spacer layer 106 is also called a resonator structure, and includes a half of an adjacent composition gradient layer and has a thickness of one wavelength. The target thickness is set. The active layer 105 is provided at the center of the resonator structure at a position corresponding to the antinode in the standing wave distribution of the electric field so as to obtain a high stimulated emission probability.

The upper semiconductor DBR 107 is stacked on the + Z side of the upper spacer layer 106, and has a low refractive index layer made of p-Al _0.93 Ga _0.07 As and a high refractive index made of p-Al _0.33 Ga _0.67 As. There are 32 pairs of layers. A composition gradient layer is provided between the refractive index layers. Each of the refractive index layers is set to have an optical thickness of λ / 4 including １ ／ of the adjacent composition gradient layer.

A selective oxidation layer made of p-Al _0.99 Ga _0.01 As is inserted into one of the low refractive index layers of the upper semiconductor DBR 107 with a thickness of 30 nm. The position where the selectively oxidized layer is inserted is in the second pair of low refractive index layers from the upper spacer layer 106.

  The contact layer 109 is stacked on the + Z side of the upper semiconductor DBR 107 and is a layer made of p-GaAs.

  Note that a structure in which a plurality of semiconductor layers are stacked on the substrate 101 in this manner is hereinafter also referred to as a “stack” for convenience.

  Next, a method for manufacturing the surface emitting laser element 100 will be described.

(1) The above-mentioned laminate is formed by crystal growth by metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE). Here, trimethylaluminum (TMA), trimethylgallium (TMG), and trimethylindium (TMI) are used as group III raw materials, and phosphine (PH ₃ ) and arsine (AsH ₃ ) are used as group V raw materials. ing. In addition, carbon tetrabromide (CBr ₄ ) and dimethyl zinc (DMZn) are used as the raw material of the p-type dopant, and hydrogen selenide (H ₂ Se) is used as the raw material of the n-type dopant.

(2) A square resist pattern having a side of 25 μm corresponding to a desired mesa shape is formed on the surface of the laminate.

(3) A square pillar-shaped mesa is formed by inductive coupling (ICP) dry etching using the resist pattern as a photomask. Here, the bottom surface of the etching is located in the lower spacer layer 104.

(4) Remove the photomask.

(5) Heat treating the laminate in steam. Here, Al in the selectively oxidized layer 108 is selectively oxidized from the outer periphery of the mesa. Then, an unoxidized region 108b surrounded by the Al oxide layer 108a is left at the center of the mesa. As a result, an oxide confined structure that limits the path of the drive current of the light emitting unit to only the center of the mesa is created. The non-oxidized region 108b is a current passing region (current injection region). Here, from the results of various preliminary experiments, heat treatment conditions (holding temperature, holding time, and the like) are appropriately selected so that the current passage region 108b has a desired size.

(6) A resist mask for forming a separation (chip cutting) groove is provided on the surface of the laminate.

(7) Using the resist mask described above as an etching mask, a groove for separation (chip cutting) is formed by a dry etching method.

(8) The protective layer 111 made of SiN is formed by using the plasma CVD method. Here, the optical thickness of the protective layer 111 was set to λ / 4. Specifically, since the refractive index n of SiN is 1.86 and the oscillation wavelength λ is 780 nm, the actual film thickness (= λ / 4n) was set to about 105 nm.

(9) An etching mask (mask M) for opening a window for the P-side electrode contact is formed on the upper portion of the mesa, which is the laser light emission surface. Here, the mask M is formed so that the annular region 111a on the mesa upper surface is not etched from the periphery of the mesa, the periphery of the mesa upper surface, and the protective layer 111 on the mesa upper surface. Here, the distance (as viewed from the Z-axis direction) between the center of the inner circumferential circle (the center of the inner diameter) of the annular region 111a and the center of the emission region in the direction perpendicular to the Z-axis is as follows. ch) is different depending on the area where it is arranged.

(10) The protective layer 111 is etched with BHF to open a window for the P-side electrode contact.

(11) The mask M is removed.

(12) A square resist pattern with a side length of 10 μm is formed in a region serving as a light emitting portion (opening of the metal layer) above the mesa, and a p-side electrode material is deposited. As the p-side electrode material, a multilayer film made of Cr / AuZn / Au or a multilayer film made of Ti / Pt / Au is used.

(13) The electrode material deposited in the region (light emission region) to be the light emission portion is lifted off to form the p-side electrode 113. An area surrounded by the p-side electrode 113 is an emission area. An annular region 111a of the protective layer 111 (hereinafter, also referred to as an annular dielectric) remains in the emission region (see FIG. 24). Here, the material of the annular dielectric (the material of the protective layer 111) is SiN, but other dielectrics such as SiO and SiO ₂ may be used.

  This annular dielectric has a function of controlling the reflectance in the emission region. That is, in the emission region, the annular portion having a dielectric is a low reflection region, and the portion having no dielectric is a high reflection region. Thus, the output of the higher-order transverse mode light can be effectively reduced without lowering the output of the fundamental transverse mode light, and the beam quality of the emitted light can be improved.

(14) After polishing the back side of the substrate 101 to a predetermined thickness (for example, about 100 μm), the n-side electrode 114 is formed. Here, the n-side electrode 114 is a multilayer film made of AuGe / Ni / Au.

(15) Ohmic conduction is established between the p-side electrode 113 and the n-side electrode 114 by annealing. Thus, the mesa becomes a light emitting unit.

(16) Each chip is cut and mounted on a ceramic package.

  Here, when the center of the annular dielectric formed in the emission region (the center of the inner circumferential circle of the annular dielectric) coincides with the center of the emission region when viewed from the Z-axis direction, the surface emitting laser array is used. The emission direction of each light emitting portion of the chip is in the + Z direction (direction perpendicular to the substrate 101), and the center of the annular dielectric and the center of the emission region are shifted (offset) when viewed from the Z axis direction. The emission direction of the light emitting portion is inclined with respect to the + Z direction (the direction perpendicular to the substrate 101). Here, in order to simplify the description, the inclination of the emission direction due to the use of the inclined substrate is not considered. The “center of the emission region” means an intersection point between an axis passing through the center of the current passing region and perpendicular to the substrate 101 (the central axis of the surface emitting laser element 100) and the emission surface (the upper surface of the contact layer 109). I do. Therefore, “the center of the emission area” may be rephrased as “the center of the emission surface”.

  Therefore, the inventors have developed a surface emitting laser array chip according to a first modification of the second embodiment in which the emission directions of a plurality of light emitting units are different by utilizing this principle.

  Referring to FIGS. 26A to 27, the light emitting unit arranges a positional relationship (offset) between the center of the annular dielectric and the center of the emission region in the surface emitting laser array chip of Modification 1 as viewed from the Z-axis direction. The following describes the offset distribution model 1 that differs depending on the region in which the offset distribution is performed. The offset distribution model 1 can be determined by designing a mask used when etching the protective layer 111.

  As shown in FIG. 26A, the surface emitting laser array chip of the first modification includes a first channel group and second to fifth channel groups arranged around the first channel group.

  More specifically, each channel group includes four channels (light emitting units) arranged in a square lattice in the X-axis direction and the Y-axis direction. The first channel group is arranged at the intersection of the diagonal lines of the square, and the second to fifth light emitting unit groups are individually arranged at the four vertexes of the square. Here, the surface emitting laser array chip and the lens are positioned such that the center of the first channel group is located on the optical axis of the lens.

  In the offset distribution model 1, an area including four channels of the first channel group, two channels on the −Y side of each of the second and third channel groups, and two channels on the + Y side of each of the fourth and fifth channel groups. (A region including a total of eight channels) is defined as an α region, a region including two channels on the + Y side of each of the second and third channel groups (a region including a total of four channels) is defined as a β region, and fourth and fifth channels are defined. A region including two channels on the −Y side of each group (a region including a total of four channels) is defined as a γ region.

  Then, in the offset distribution model 1, the offset of the channel in the Y-axis direction (at least one of the shift amount and the shift direction in the Y-axis direction from the center of the emission region at the center of the annular dielectric viewed from the Z-axis direction) is set between the regions. Is different.

  FIG. 27 is a graph showing the relationship between the offset of the channel in the Y-axis direction and the inclination angle of the emission angle with respect to the Z-axis.

  From FIG. 27, it can be seen that the emission direction changes in each channel due to the offset in the Y-axis direction. More specifically, the emission direction of each channel is inclined in the opposite direction (+ Y direction or + Y direction) to the offset direction in the Y axis direction (+ Y direction or -Y direction) with respect to the Z axis, and the inclination angle is offset. It is almost proportional to the amount.

  In the first modification, when the center of the annular dielectric and the center of the emission region coincide with each other when viewed from the Z-axis direction due to the use of the substrate 101 (inclined substrate) inclined around the X axis. The emission direction is shifted by about 0.1 ° in the + Y direction (see FIG. 27).

  Therefore, in the first modification, as shown in FIG. 26B, the center of the annular dielectric is set to the emission region so that the inclination angle of the emission direction of each channel of the α region with respect to the Z axis is 0.0 °. Is offset by 0.2 μm in the + Y direction with respect to the center of.

  Further, as shown in FIG. 26C, the annular dielectric is set such that the emission direction of each channel in the β region is inclined at a desired angle δ (about 0.15 °) in the −Y direction with respect to the Z axis. The center of the body is offset by 0.5 μm in the + Y direction with respect to the center of the emission area.

  Further, as shown in FIG. 26 (D), the annular dielectric is set so that the emission direction of each channel in the γ region is inclined at a desired angle δ (about 0.15 °) in the + Y direction with respect to the Z axis. Is offset by 0.1 μm in the −Y direction with respect to the center of the emission region.

  Next, an offset distribution model 2 according to a second modification will be described with reference to FIGS. In the surface emitting laser element of the second modification, unlike the first modification, no inclined substrate is used. That is, the normal direction of the mirror-polished surface of the substrate of the surface emitting laser element of Modification 2 matches the crystal orientation [100] direction.

  In the offset distribution model 2, a region including four channels of the first channel group, two channels on the + X side of each of the second and fifth channel groups, and two channels on the -X side of each of the third and fourth channel groups. A region including a total of four channels (a region including a total of four channels) is defined as an α ′ region, and a region including two channels on the −X side of each of the second and fifth channel groups is defined as an α ′ region. A region including two channels on the + X side of each of the fourth and fourth channel groups (a region including a total of four channels) is defined as a γ ′ region.

  In the offset distribution model 2, the offset of the channel in the X-axis direction (at least one of the shift amount and the shift direction in the X-axis direction from the center of the emission region at the center of the annular dielectric as viewed in the Z-axis direction) is set between the regions. Is different. Note that, similarly to the offset in the Y-axis direction (see FIG. 27), the offset in the X-axis direction has a linear relationship between the offset amount and the inclination angle in the emission direction.

  Specifically, in the α ′ region, the annular dielectric is not offset with respect to the emission region (see FIG. 28B). That is, in the α ′ region, the center of the annular dielectric coincides with the center of the emission region when viewed from the Z-axis direction, and the emission direction of each channel is parallel to the Z-axis.

  In the β 'region, the center of the ring-shaped dielectric is-with respect to the center of the emission region so that the emission direction of each channel is inclined at a desired angle δ (about 0.15 °) in the + X direction with respect to the Z axis. It is offset by 0.3 μm in the X direction (see FIG. 28C).

  In the γ ′ region, the center of the annular dielectric is positioned with respect to the center of the emission region so that the emission direction of each channel is inclined at a desired angle δ (about 0.15 °) in the −X direction with respect to the Z axis. It is offset by 0.3 μm in the + X direction (see FIG. 28D).

  The offset distribution models 1 and 2 described above are examples of offsetting in the Y-axis direction and the X-axis direction, respectively, but may be offset in both the X-axis direction and the Y-axis direction. In this case, the emission direction can be inclined in the + X direction or -X direction and the + Y direction or -Y direction with respect to the Z axis.

  Further, as in the offset distribution model 3 of the surface emitting laser array chip of Modification 3 shown in FIG. 29, the offsets of the four channels of each channel group may be different from each other.

  That is, the offset distribution model is not limited to the offset distribution models 1 to 3 of Modifications 1 to 3, and can be appropriately changed.

  As shown in FIG. 30, for example, when the emission directions of a plurality of adjacent channels in a surface emitting laser array chip are parallel, a plurality of beams emitted from the plurality of channels and incident on a subject via a lens and a prism are provided. The incident position of the light on the subject was shifted, for example, by about 10 μm.

  On the other hand, as shown in FIG. 31, for example, the emission direction of the outermost channel in the surface emitting laser array chip is inclined by 0.3 [deg] toward the optical axis side of the lens with respect to the Z axis (optical axis of the lens). If the emission direction of the outermost ch and the ch adjacent to the ch (ch whose emission direction is parallel to the Z axis) is set to be non-parallel, the light emitted from these ch is passed through the lens and the prism to the subject. The displacement of the incident positions of the plurality of incident lights on the subject could be reduced (to approximately 0 μm).

  That is, one of the emission directions of the two adjacent channels in the periphery of the surface emitting laser array chip is inclined with respect to the optical axis of the lens so as to approach the other side, so that the two channels receive two lights. The displacement of the incident position on the sample can be reduced.

  On the other hand, regarding two channels (see FIG. 31) adjacent to each other across the optical axis of the lens at the center of the surface emitting laser array chip, the emission directions of the two channels are set parallel to the Z axis (optical axis of the lens). Also, since the light emitted from the two channels is refracted by the lens in the direction approaching each other, the one of the emission directions of the two adjacent channels is not inclined with respect to the optical axis of the lens so as to approach the other side. However, the deviation of the incident position on the subject can be reduced. However, even in this case, by inclining one of the emission directions of the two adjacent channels with respect to the Z axis so as to approach the other side, two lights from the two channels enter the subject. The displacement can be made smaller. In FIG. 31, light from the central channel of the surface emitting laser array chip can be incident on the subject only through the lens (not through the prism).

  As can be understood from the above description, in the first to third modifications, by setting the emission directions of the plurality of channels of the surface emitting laser array chip to be non-parallel, the plurality of lights from the plurality of channels are transmitted to the subject. The shift of the incident position can be reduced. Therefore, even when the distance between the probes is reduced and the probes are arranged at a high density, the identity of the incident positions can be increased, and the resolution can be increased.

  In the surface emitting laser array, the lens, and the prism, the optical path of light emitted from each of at least two light emitting units, transmitted through the lens, and reflected by the reflecting member is near the emission end of the light source module LM (near the surface of the subject). It is preferable to configure and lay out such that they intersect.

  In the first to third modifications, the emission directions of all the channels of the surface-emitting laser array chip do not necessarily need to be non-parallel to each other. In short, the emission directions of at least two channels of the surface-emitting laser array chip are changed. What is necessary is just to make them non-parallel. For this purpose, the center of the annular dielectric of at least one channel may be shifted from the center of the emission region.

  Also, it is not necessary to provide a ring-shaped dielectric in the emission regions of all the light-emitting portions of the surface-emitting laser array chip, and the ring-shaped dielectric is provided only in the emission region of the light-emitting portion whose emission direction should be inclined with respect to the optical axis of the lens. It may be provided. The presence or absence of the annular dielectric in each channel can be determined by designing a mask used when etching the protective layer 111.

  The dielectric material provided in the emission region may not be strictly annular, and may be, for example, one in which at least one annular portion is interrupted (a combination of a plurality of arcs having the same diameter and the same diameter as viewed from the Z-axis direction). ). Further, the dielectric material provided in the emission region is not limited to a substantially annular shape, and it is only necessary that the dielectric material has a substantially frame shape.

  By the way, in the light source module of the comparative example shown in FIG. 32A in which a plurality of light beams parallel to each other enter the living body, a detection error occurs when there is an altered portion near the surface of the living body. The “altered portion” means a portion having a special optical property, such as a hair root or colored skin. In the comparative example, since the light from the light source 1 and the light source 2 is incident on different positions of the subject when such a deteriorated portion exists, for example, a case where only the light from the light source 2 passes through the deteriorated portion occurs. I do. When the difference between the light source 1 and the light source 2 is calculated, the altered portion becomes noise.

  On the other hand, in the present embodiment, as shown in FIG. 32B, the light from the light source 1 and the light source 2 pass through the “same position” on the skin surface, and When light passes through the altered portion, light from the other also passes through the altered portion. When light from one of the light sources 1 and 2 does not pass through the altered portion, light from the other does not pass through the altered portion. More specifically, the light from the light source 1 and the light from the light source 2 have the same optical path near the skin surface and pass through different optical paths in the depth direction. That is, the structure is insensitive to the difference near the skin surface, but is sensitive to the difference near the brain tissue. The resolution is improved by reducing the noise near the skin surface.

  In the second embodiment, a transparent gel is dropped on the window member provided in the housing, and a transparent gel is interposed between the window member and the surface of the subject to prevent air from entering.

  In a conventional light source module, light once radiated into the air propagates from the skin surface into the body. At this time, a refractive index difference occurs between a refractive index of 1.0 in air and a refractive index of 1.37 of a living body. When a difference in refractive index occurs, reflection and scattering occur. Further, since the refractive index in the living body through which light propagates is smaller than that of air outside the living body, the propagation angle in the living body (also referred to as the living body propagation angle) becomes smaller than the incident angle. The refraction of light at the interface can be understood by using Snell's equation. This Snell equation can be described only by the refractive index.

  FIG. 33 is a graph showing the relationship between the incident angle at the interface between 1.0 (air: incident side) and 1.37 (living body: propagation side) and the propagation angle in the living body (light refraction). Have been. As can be seen from FIG. 33, even if the incident angle of the light on the living body is 60 degrees, the light propagation angle in the living body becomes as small as 40 degrees. For this reason, even if the propagation angle of light in the living body is required to be 60 degrees or more, it can be understood that it cannot be realized by the incidence of light from the air. In other words, it is difficult to create a large propagation angle in a living body with light once emitted into the air.

  Therefore, in the second embodiment, the refractive index of the transparent resin that is the material of the window member of the light source module LM is set to a refractive index (for example, 1.5 or more) larger than the refractive index of the living body of 1.37 (FIG. 34). In this case, the propagation angle in the living body of the light directly incident on the living body at the incident angle of 60 degrees from the light source module LM exceeds 70 degrees. When considering the design of the light source module LM, it is advantageous to make this angle as small as possible, for example, the size of the light source module LM can be reduced.

  In the light source module LM according to the second embodiment configured as described above, as illustrated in FIG. 16, light emitted from the surface emitting laser in a direction parallel to the optical axis of the lens is refracted by the lens, and The light travels in a direction inclined by about 20 ° with respect to the optical axis, and enters the window member. The refractive index of this window member is set to about 1.5. The light passing through the lens is refracted when entering the window member, but is not large refraction due to a large angle of incidence. The light incident on the window member is deflected by the reflecting surface of the prism and travels in a direction inclined by about 55 ° with respect to the optical axis of the lens. This 55 ° angle is an angle in the window member having the refractive index of 1.5, and as shown in FIG. 34, the propagation angle in the living body (refractive index: 1.37) is about 60 degrees. .

  In order for light to directly propagate from the light source module LM into the simulated living body, it is necessary to remove an air layer entering the interface between the simulated living body and the light source module LM. Here, a transparent gel was used for removing the air layer. The transparent gel used here was an aqueous glycerin solution, and a gel having good compatibility with the simulated living body was selected. In addition, the transparent gel was adjusted for volatility so that it did not evaporate during the test, that is, while the light source module LM was covered, and was adjusted to permeate the volatilized or simulated living body at an appropriate timing after the test. . The optical properties of the transparent gel are transparent near the wavelength of 780 nm, and the refractive index is adjusted to a value close to the surface of the simulated living body. In this case, the mixture was prepared to be about 1.37. By this preparation, even if there are irregularities on the surface of the simulated living body, there is no difference in refractive index between the irregular surfaces and there is no reflection at all. Thereby, the reflection on the surface of the simulated living body could be almost eliminated. Further, even if the interface with the simulated living body is physically uneven, there is no optical unevenness, so that no scattering occurs. As a result, the light can be accurately propagated inside the simulated living body in an appropriate propagation direction according to the emission angle of the light from the light source module LM. Generally, the propagation inside the simulated living body causes strong scattering, but the scattering on the skin surface is not small. Thereby, large anisotropy of light can be secured. By obtaining a large anisotropy, the incident angles of a plurality of lights from the light source module LM to the simulated living body can be greatly changed, and the angles of incidence of the plurality of lights to the detection module DM can be largely changed as described later. Can be.

  As shown in FIG. 35, the detection module DM includes a flexible board (not shown) on which a housing, an optical element, a light receiving section, and an analog electronic circuit are mounted, wiring connected to the flexible board, and a connector section (not shown). ).

  In the detection module DM, as shown in FIG. 36, the light emitted from the light source to the simulated living body and propagated through the simulated living body is divided into a plurality of lights and guided to a plurality of light receiving units.

  In the related art (see Japanese Patent Application Laid-Open No. 2011-179903), in a DOT using fluorescence, a light receiving unit is arranged in correspondence with a plurality of lights emitted from a subject at multiple angles. However, in this arrangement of the light receiving unit, the light incident on the light receiving unit is light at all emission angles from the subject.

  On the other hand, the detection module DM of the present embodiment divides the light from the “same position” of the subject and individually detects the light. As described in the light source module LM, since it can be designed at the time of the optical simulation, the accuracy of the “same position” does not matter whether the position is in the order of mm.

  Hereinafter, the detection module DM will be described in detail. As shown in FIG. 37, the detection module DM includes a black resin housing, a contact member made of an elastic body attached to the tip of the housing, a transparent split lens housed in the housing, and four light receiving units. It is comprised including. An aperture (opening) is formed at the tip of the housing and the contact member.

  As the contact member, a black rubber member is used in order to enhance the light shielding property. From the aperture of the contact member, the central portion (about 1 mm) of the split lens projects out of the housing by about several 100 μm. Since this portion comes into contact with the surface of the living body, refraction and scattering of Fresnel are suppressed without air being present optically.

  Also, in the detection module DM, since the stability is further improved by using the above-described transparent gel, the transparent gel is used. The split lens is made of a transparent resin and has a refractive index of about 1.8. The split lens is fixed to the housing.

  The aperture is a circular hole of about 1 mm penetrating the tip of the housing and the contact member, and has a function of limiting the position of light that propagates and exits inside the subject. The light coming out of this position is directed in a plurality of different directions, and the incident position is defined by an aperture, and then the incident light is divided into a plurality of lights by a split lens, and the plurality of lights are individually detected. Can be.

  The light from the subject described above is incident on the light receiving unit from the “same position” by the aperture.

  The light that has passed through the aperture is refracted in different directions by the split lens depending on the propagation direction of the light, and thus the incident position on the light receiving unit is different.

  The split lens is a spherical lens having a diameter of about 3 mm and a focal length f of about 3 mm. In the second embodiment, the number of light divisions by the division lens is set to 4, and a PD array (photodiode array) including four light receiving units (PD: photodiodes) arranged two-dimensionally is used. FIG. 37 shows only two light receiving units 1 and 2 of the four light receiving units (PD).

  Here, the PD array has a square shape with a side length of about 3 mm, and each PD has a square shape with a side length of 1.4 mm. The angle θ2 as shown in FIG. 37 was defined, and the distance between the PD array and the aperture was set to about 5 mm.

  One surface of the lens is flat, and only one surface has a spherical surface. The plane is in contact with the simulated living body. Since the position of the aperture is different from the focus position of the lens, parallel light cannot be produced, but has a function of limiting light incident on the PD array.

  When a simple optical simulation is performed on this optical system, light of approximately −10 ° <θ2 <50 ° enters the light receiving unit 2 and light of approximately −50 ° <θ2 <10 ° enters the light receiving unit 1. It turns out. That is, the light that propagates through the simulated living body and is emitted from the aperture is divided into a plurality of lights according to the emission angle, and each of the plurality of lights is incident on one of the four light receiving units.

  In the second embodiment, a spherical lens is used as the split lens, but an aspheric lens can be used to detect a wider angle. Since the division accuracy and the number of divisions have a correlation with the estimation accuracy of the inverse problem described later, the required optical system is determined from the desired estimation accuracy. In the present embodiment, a spherical lens and a division number of 4 are employed.

  Each PD is electrically wired and connected to an operational amplifier. A semiconductor operational amplifier is used for the amplifier, and a power supply voltage of 5 V is supplied. Since the amount of light to be detected is very small, the magnification in the operational amplifier is high, and a two-stage amplifier configuration is used. A magnification of about 5 digits is applied in the first stage, and a magnification of about 3 digits is applied in the second stage.

  In Example 2, a method for measuring the position of the light absorber existing in the simulated living body (method for detecting the optical characteristics of the subject) will be described with reference to the flowchart shown in FIG.

First, the probes (light source module LM and detection module DM) are set (attached) to the simulated living body (step S1). At this time, apply a transparent gel between the acrylic water tank and each probe, and carefully set each probe to the position determined by the fixing member while checking each probe so that air bubbles do not enter the transparent gel. .
The probe has eight light source modules LM and eight detection modules DM, for a total of 16, and the light source modules LM and the detection modules DM are alternately arranged in a grid at an equal pitch (see FIG. 15). The pitch of the grating (grid point interval) is 30 mm, and the interval between the light source module LM and the detection module DM is 30 mm.

  In this state, the channel of any one light source module LM emits light (step S2). Light emission is performed for each group (4 ch), and the current value is determined so that the light emission intensity is about 4 mW. The light emission time is about 10 msec. During this time, the detection values of all PDs are read, and data at several points detected at 1 msec intervals are averaged (step S3). Then, the averaged numerical value is stored in the recording unit (step S4). Similarly, the next group repeats light emission, measurement, and data storage for 10 msec (steps S5, S6, S2 to S4). In addition, in one light source module LM, light emission of 4ch of the surface emitting laser array chip having the oscillation wavelength of 780 nm and light emission of 4ch of the surface emitting laser array chip having the oscillation wavelength of 900 nm are sequentially performed in the same manner.

  However, in the following data processing, two wavelengths are treated in substantially the same manner, and the measurement at the same position is simply performed twice each. When detecting a change in the original blood flow, oxyhemoglobin and reduced hemoglobin are individually detected by utilizing the difference between the two wavelengths. In this embodiment, two surface emitting lasers having different oscillation wavelengths are used. By performing measurement once using an array chip, noise due to chip variation can be reduced.

When the light emission and measurement of all the groups of one light source module LM are completed, light emission of the next light source module LM is performed (steps S7, S8, S2 to S4). In this case, the light emission is also sequentially performed for each group (4 channels). When light emission and measurement by all the light source modules LM are completed, the light absorber is set (steps S9 and S10). The setting of the light absorber is performed using an optical stage so that the position can be accurately realized with good reproducibility. With the light absorber set, the numerical value of the PD is recorded again from the ch light emission (steps S2 to S9).
The stored data are the data with and without the light absorber, respectively, and the data without the light are represented by the following r (s, i, n) (i = 1, 2, 3,... M, n = 1, 2, 3,... K) ), R (0, i, n) (i = 1, 2, 3,... M, n = 1, 2, 3,... K). i is a number assigned to each detection module DM. n is a number assigned to each group. Next, each difference Δr (i, n) is calculated.

  The method of calculating the position of the light absorber (optical characteristics of the simulated living body) from the measurement result obtained by the above-described position measurement method is based on the position of the light absorber (from the measurement result obtained by the measurement method based on the flowchart of FIG. 8 described above). The method is the same as the method for calculating the optical characteristics of the simulated living body), and thus the description is omitted.

  As a result, an estimation result as shown in FIG. 39 can be derived. FIG. 39 shows a comparative example in which only one central group (see FIG. 17) out of five groups of surface emitting laser array chips emits light, and only the detected value of one of the four PDs in the PD array is displayed. The results of detection using the data are also shown. Otherwise, numerical processing is performed in the same manner as in the present embodiment. This comparative example has substantially the same configuration as a conventional NIRS (DOT) device. In the present embodiment, the position and depth of the light absorber can be detected by the Bayes estimation. In the results shown in FIG. 39, ○ (circle) is displayed when the position of the light absorber was detected. In the present embodiment, when the distance in the depth direction (here, the Z-axis direction in FIG. 10) of the light absorber increases, the distance from the light source module LM increases, and the amount of light that can propagate decreases. For this reason, the detection becomes more difficult as the depth of the position of the light absorber increases. In the present embodiment, detection was possible up to about 16 mm. The comparative example is a general NIRS (DOT) device, and it was not possible to detect in the depth direction using Bayesian estimation. In order to detect the three-dimensional position of the light absorber including the depth with high precision by DOT, generally a high-density probe arrangement is required, but in the present embodiment, this can be realized by a low-density probe arrangement. .

  The optical sensor 10 of the present embodiment (Examples 1 and 2) described above irradiates a subject (simulated living body) with light, and includes an irradiation system including a plurality of light source modules LM (light irradiators); A detection system for detecting light emitted from the device and transmitted through the subject. Then, each of the plurality of light source modules LM irradiates the non-parallel light to the same position of the subject. In this case, a plurality of non-parallel lights irradiating the same position of the subject (scatterer) have different incident angles to the subject and follow different propagation paths (see FIG. 40).

  As a result, the amount of information obtained regarding the inside of the subject increases, and higher resolution can be achieved. Also, by increasing the resolution, for the same required resolution, the probe density (the number of probes per unit area) can be reduced, and the mountability can be improved.

  As a result, with the optical sensor 10, high resolution can be obtained without lowering the mountability to the subject.

  Note that the fact that a plurality of lights incident on the same position of the subject are non-parallel means that the plurality of lights form an angle. That is, the existence of the angle formed by the plurality of lights makes it possible to make the propagation paths of the plurality of lights in the subject different. On the other hand, if a plurality of lights incident on the same position of the subject are parallel to each other (for example, parallel to the surface normal of the subject), the propagation paths of the plurality of lights in the subject are the same. turn into.

  Further, the light source modules LM of Modifications 1 to 3 of the second embodiment include a surface emitting laser array chip having a plurality of light emitting units (ch) and a lens arranged on the optical path of a plurality of lights from the plurality of light emitting units. And the emission directions of at least two of the plurality of light emitting units are non-parallel.

  In this case, the displacement of the incident positions of the plurality of lights from the plurality of channels on the subject can be reduced, so that the probes (the light source module LM and the detection module DM) can be arranged at a high density, and the resolution can be further increased. Can be achieved.

  In addition, each of the plurality of light emitting units has an annular dielectric in the emission region, and at least one of the plurality of light emitting units has a center of the annular dielectric shifted from the center of the emission region. The emission direction can be controlled while improving the beam quality.

  In addition, since the emission direction of at least one light emitting unit is inclined with respect to the optical axis of the lens, the direction of refraction (the traveling direction) from the lens can be adjusted.

  In addition, since at least two light emitting units have different positional relations between the center of the dielectric and the center of the emission region, the emission directions of the at least two light emission units can be surely non-parallel.

  In addition, since the optical paths of the light from each of the at least two light emitting units to the lens are gradually approaching, the optical paths of the light emitted from the at least two light emitting units can be further approximated by the lens (see FIG. 31).

  The light source module LM includes a prism having a reflecting surface that is disposed on an optical path of light emitted from each of at least two light emitting units and passes through a lens and reflects the light toward a subject. It can be guided to the same position of the subject.

  In addition, the light source module LM of the present embodiment is arranged on a surface emitting laser array having a plurality of surface emitting lasers (light emitting units), on a light path of a plurality of lights from the plurality of surface emitting lasers, and Is a plurality of non-parallel light beams, and the distance between the principal point of the convex lens and the surface emitting laser array does not match the focal length of the convex lens.

  In this case, return light can be prevented from being condensed on the surface emitting laser, and output fluctuation of the surface emitting laser can be prevented. As a result, the light emission amount of the surface emitting laser can be stabilized, the detection accuracy of the optical sensor 10 can be improved, and the resolution of the NIRS can be improved.

  On the other hand, when the surface emitting laser array is located at the focal position of the convex lens, the light reflected from the external reflecting surface is focused on the surface emitting laser by the convex lens, and the laser oscillation becomes unstable. This is a phenomenon called a return light or a self-mixing phenomenon. When this phenomenon occurs when the surface emitting laser array is used as a light source of an optical sensor, the amount of emitted light becomes unstable, which causes a problem. Japanese Patent Application Laid-Open Nos. 2011-114228 and 2012-132740).

  The space between the convex lens and the surface emitting laser array is filled with a transparent resin having a refractive index equivalent to that of the convex lens.

  In this case, since the refractive index does not change at the interface between the convex lens and the surface emitting laser array, return light can be suppressed. As a result, the amount of light emitted from the surface emitting laser array can be stabilized, and the resolution of NIRS can be improved.

  Further, the detection system has a plurality of detection modules DM including a plurality of light receiving units (PDs) that individually receive a plurality of lights emitted from the light source module LM to the subject and propagated in the subject.

  In this case, two pieces of information on two different propagation paths in the subject can be obtained individually.

  Further, the detection module DM is disposed between the subject and the plurality of light receiving units (PD), and is provided with a contact member and a housing provided with an aperture for passing a part of each of the plurality of lights propagated in the subject. have.

  In this case, light can be taken into the housing from the same position of the subject, that is, only light whose incident angle is limited to a certain extent from the subject can be made to enter the housing, and light can be easily made to enter a plurality of light receiving portions. can do.

  Further, the detection module DM has a split lens (light receiving lens) that individually guides a part of the plurality of lights that have passed through the aperture to the plurality of light receiving units.

  In this case, a part of each of the plurality of lights that have passed through the aperture can be individually incident on the plurality of light receiving units with a stable light amount.

  In addition, since the light source module LM has a window member made of a material (transparent resin) having a refractive index higher than that of the subject and being in contact with the subject, the light source module LM has a position in the subject that is different from the incident angle to the subject. Can be increased. As a result, the propagation angle is increased even at the same incident angle as compared to a case where light is incident on the subject from the air. Therefore, the difference between the angles of propagation of these two lights in the subject is greater than the difference between the angles of incidence of the two lights that enter the same position of the subject at different angles of incidence, and the propagation paths are greatly different. be able to. As a result, higher resolution can be achieved.

  The light source module LM includes a plurality of two-dimensionally arranged surface emitting lasers and an irradiation lens (lens) arranged on an optical path of light from the plurality of surface emitting lasers.

  In this case, the traveling direction of the light from the plurality of surface emitting lasers can be changed to a desired direction (the direction in which the corresponding prism is arranged).

  The light source module LM has a prism (reflection member) that is arranged on the optical path of light passing through the irradiation lens and reflects the light in a predetermined direction.

  In this case, the traveling direction of light from the irradiation lens can be further changed to a desired direction. That is, the angle of incidence on the subject can be set to a desired angle.

  As described above, the optical sensor 10 is an optical sensor that can achieve high resolution by effectively utilizing light propagation anisotropy with a simple configuration, and is expected to be used in various fields such as DOT. You.

  Further, the optical inspection apparatus 1000 includes the optical sensor 10 and a control unit (optical characteristic calculation unit) that calculates the optical characteristics of the subject based on the detection result of the optical sensor 10.

In this case, since the detection accuracy of the optical sensor 10 is high, the optical characteristics of the subject can be calculated with high accuracy.
<< 2nd Embodiment >>

  Next, a second embodiment of the present invention will be described. In the present embodiment, a method for adapting the probe described in the first embodiment to an actual human body will be described. Here, the subject is changed from the phantom (water tank containing cloudy water) in the above embodiment to the head of the human body, and the light absorber is used as the blood flow in the brain.

  The purpose of the present embodiment is to accurately estimate the distribution of blood flow in the brain. In the present embodiment, a subject (subject) is measured, a shape is modeled based on the data, and a Monte Carlo simulation is performed. The shape of the subject's head is measured using nuclear magnetic resonance imaging (MRI). The shape of the four parts of the scalp, skull, cerebrospinal fluid, and cerebral cortex are measured from the image.

  The three-dimensional data is necessary for high-precision detection, but can be replaced with data such as a brain model having a standard shape. The general values of the scattering coefficient, anisotropy, and absorption coefficient are known for each part, and the values are used. The probe is accurately fixed to the head with a fixing jig, and the installed position is also measured accurately. Since the probe and the like are the same as in the first embodiment, the description is omitted here. An optical simulation is performed using the exact shape, arrangement, and numerical values of each part.

  Hereinafter, a method of measuring the blood flow in the brain will be described with reference to the flowchart shown in FIG. First, the subject is first allowed to rest (step S31), and the probe (detection module DM and light source module LM) is set on the head. At this time, the probe is carefully set (installed) at a predetermined position using a fixing member while checking each probe so that hair and the like do not get caught between the probe and the scalp. In this state, the channel emits light (step S33). Light emission (pulse light emission) is performed for each group, and the current value is determined so that the intensity is about 4 mW. The light emission time is several msec, during which the detected values of all PDs are read and averaged (step S34). The averaged numerical value is stored in the recording medium (step S35).

  Similarly, the next group repeats light emission, measurement, and data storage for several milliseconds (steps S36, S37, and S33 to S35). When the light emission and measurement of all the light source modules LM have been completed, the subject is asked to perform a task (steps S38 to S41). Here, a general language fluency task was used. The linguistic fluency task is described in detail in Japanese Patent Application Laid-Open No. 2012-080975.

By performing this task, the brain is activated and cerebral blood flow is generated only at the location where the activity occurred. The bloodstream contains oxyhemoglobin and reduced hemoglobin, and light absorption occurs by the bloodstream. The inverse problem estimation based on Bayes estimation and the like follow the method described in the first embodiment, and will not be described here. With this measurement, the accuracy of the obtained blood flow position can be confirmed by measurement with fMRI (functional magnetic resonance imaging). fMRI is a method of visualizing hemodynamic responses related to brain and spinal cord activity of humans and animals using MRI. From this confirmation measurement, it was found that the measurement by the optical sensor of the present embodiment had high resolution.
<< 3rd Embodiment >>

  Next, a third embodiment of the present invention will be described. In the third embodiment, a light source module LM and a detection module DM similar to those in the first embodiment are used as probes, and the arrangement of these modules is devised. Except for the arrangement of the probes, the configuration is the same as that of the above-described first embodiment, and the description is omitted here.

By the way, in Example 2 of the first embodiment, as shown in FIG. 15, two detection modules DM and two light source modules LM are arranged so as to be located at the vertices of a substantially square. However, in this arrangement, the optical path between the light source module LM and the detection module DM becomes long at the point indicated by x in FIG. For this reason, a sufficient amount of light cannot be obtained by the detection module DM, and noise at this point may be large and detection accuracy may be reduced.
Then, the present inventors diligently studied the probe arrangement and found that the arrangement shown in FIG. 42 was optimal. In FIG. 42, the plurality of light source modules LM and the plurality of detection modules DM are such that, with respect to the subject, one of the light source modules LM and the detection modules DM is individually located at two vertexes of an equilateral triangle, and the other 1 Are arranged so as to be located at one remaining vertex of the equilateral triangle.

  Here, as a simple example, a case where the distance between the light source module LM and the detection module DM is the longest will be considered. However, it is assumed that the interval (pitch) between the detection module DM and the light source module LM is a. In the position of x in FIG. 15, the distance of the broken line is √2a (about 1.414a). On the other hand, at the position of x in FIG. 42, the distance of the broken line is (1 + √3) a / 2 (about 1.366a) <√2a. That is, comparing the longest distance with the probe arrangement of FIG. 15 and FIG. 42, it can be seen that the probe arrangement of FIG. 42 is shorter and preferable.

As a result of estimating the inverse problem in this arrangement in the same manner as in the first embodiment, it was found that the detectable area was expanded by the probe arrangement of the present embodiment.
<< 4th Embodiment >>

  Next, a fourth embodiment of the present invention will be described. In the fourth embodiment, the arrangement of the channels of the light source module LM and the arrangement of the PDs of the detection module DM are devised by utilizing the arrangement of the plurality of light source modules LM and the plurality of detection modules DM shown in the first embodiment. ing. Except for the arrangement of channels and PDs, the configuration is the same as that of the first embodiment, and a description thereof will be omitted.

  In Example 2 of the first embodiment, as shown in FIG. 15, the plurality of light source modules LM and the plurality of detection modules DM are such that the light source module LM and the detection module DM are orthogonal to the subject. They are arranged adjacent to each other in both the X and Y directions.

  However, as described above, in this arrangement, the optical path between the light source module LM and the detection module DM becomes long at the point indicated by x. For this reason, a sufficient amount of light cannot be obtained by the detection module DM, the noise at this point increases, and the detection accuracy may be reduced.

  In the comparative example shown in FIG. 43, the plurality of light source modules and the plurality of detection modules are arranged such that the light source module and the detection module are adjacent to the subject in both the X direction and the Y direction orthogonal to each other. In addition, both the emission direction and the detection direction (the direction in which light enters the light receiving unit) are parallel to the X direction or the Y direction. Since the lens installed near the surface emitting laser has point-symmetric optical characteristics, the emission direction is determined by the position of the surface emitting laser and the group position. The detection direction is also determined by the PD array division layout since the lens has point-symmetric optical characteristics.

  Therefore, when the surface emitting laser array chip is arranged as shown in FIG. 44A, the emission direction is inclined with respect to the X direction and the Y direction in plan view (when viewed from the + Z direction). This is because the center position of each group is oblique to the lens center. Similarly, in the detection module DM, by arranging the center of the lens at the center of the four-divided PD array array chip (photodiode array chip), the detection direction (the direction of light incident on the light receiving unit) is as shown in FIG. ). The detection direction and the emission direction are shown in FIG. 45 together with the probe arrangement. It can be seen that the emission direction and the detection direction are oblique to the X direction and the Y direction (when viewed from the + Z direction) in plan view.

  In this case, since the light has anisotropy as in the above-described sensitivity distribution, it can be expected that the light has higher sensitivity at the position x in FIG.

  As a result of estimating the inverse problem in the arrangement shown in FIGS. 44A and 44B in the same manner as in the first embodiment, it was found that the area that can be detected is widened.

  In each of the above embodiments, the number of light source modules LM of the irradiation system and the number of detection modules of the detection system can be changed as appropriate. In short, the irradiation system only needs to have at least one light source module LM. The detection system only needs to have at least one detection module DM.

  In each of the above embodiments, the configuration of the light source module LM (light irradiator) can be changed as appropriate. For example, the number and arrangement of the surface emitting laser array chips of the light irradiator can be appropriately changed. The type, shape, size, number, and the like of the lenses can be appropriately changed.

  In each of the above embodiments, a surface emitting laser is used as a light source of the light irradiator. For example, an edge emitting laser (LD), a light emitting diode (LED), an organic EL device, a laser other than a semiconductor laser, or the like May be used.

  Further, in each of the above embodiments, the prism is used as the reflection member of the light irradiator, but another mirror or the like may be provided.

  Further, the number and arrangement of groups in the surface emitting laser array chip of the second embodiment, and the number and arrangement of channels in each group can be changed as appropriate.

  Further, the configuration of the detection module DM (photodetector) can be changed as appropriate. For example, the aperture need not necessarily be provided. Also, for example, the split lens need not always be provided.

  The shapes, sizes, materials, numbers, dimensions, and numerical values of the members and portions in the above description are merely examples, and it goes without saying that they can be changed as appropriate.

  10: Optical sensor, 1000: Optical inspection device, LM: Light source module (light irradiator), DM: Detection module (light detector).

Japanese Patent No. 3779134

Claims (14)

An irradiation system including at least one light irradiator that irradiates a plurality of non-parallel lights to the same position of the subject;
A detection system that detects light emitted from the irradiation system and propagated in the subject,
The light irradiator,
A surface emitting laser array having a plurality of light emitting units,
A lens disposed on an optical path of a plurality of lights from the plurality of light emitting units,
Light through the lens is emitted from at least two light emitting portions of the plurality of light emitting portions Ri nonparallel der each other,
Wherein the plurality of light emitting portions each have a generally annular dielectric emission region, at least one light emitting portion of the at least two light emitting portion, that the center of the dielectric is not offset from the center of the emission region An optical sensor, comprising: Wherein the emission direction of the at least one light emitting unit, an optical sensor according to claim 1, characterized in that it is inclined to the optical axis of the lens. Wherein the at least two light emitting portions, the optical sensor according to claim 1 or 2, characterized in that the positional relationship between the center of said exit region of the dielectric are different from each other. The light irradiator further includes a member disposed on an optical path of light emitted from each of the at least two light emitting units and passing through the lens, and having a reflection surface that reflects the light. An optical sensor according to any one of claims 1 to 3 . The optical sensor according to any one of claims 1 to 4 , wherein a refractive index between the lens and the surface emitting laser array is filled with a transparent resin equivalent to that of the lens. The detection system of claim 1 to 5, characterized in that the radiation containing said at least one light detector including a plurality of light receiving portions for receiving a plurality of light propagated within the object from the light irradiator The optical sensor according to claim 1. The light detector,
A member disposed between the subject and the plurality of light receiving units, and provided with a passing unit configured to pass a part of each of the plurality of lights propagated in the subject. 7. The optical sensor according to 6 . The light detector,
The optical sensor according to claim 7 , further comprising a light receiving lens that individually guides a part of the plurality of lights passing through the passing unit to the plurality of light receiving units. The irradiation system includes a plurality of the light irradiators,
The detection system includes a plurality of the photodetectors,
The plurality of light irradiators and the plurality of light detectors are arranged such that, with respect to the subject, the light irradiators and the light detectors are adjacent to each other in any two directions orthogonal to each other,
The emission direction of the plurality of lights from each of the plurality of light irradiators is inclined with respect to the two directions,
The optical sensor according to any one of claims 6 to 8 , wherein an incident direction of light propagating in the subject and entering the photodetector is inclined with respect to the two directions. . The irradiation system includes a plurality of the light irradiators,
The detection system includes a plurality of the photodetectors,
The plurality of light irradiators and the plurality of light detectors are such that, with respect to the subject, one of the two light irradiators and the light detector is individually located at two vertexes of an equilateral triangle, and the other is The optical sensor according to any one of claims 6 to 8 , wherein one is disposed so as to be located at one remaining vertex of the equilateral triangle. The optical sensor according to any one of claims 1 to 10 , wherein the light irradiator has a member that is in contact with the subject and is made of a material having a higher refractive index than the subject. . The lens is an optical sensor according to any one of claims 1 to 11, characterized in that it has a shape which is convex in the surface emitting laser array side. An optical sensor according to any one of claims 1 to 12 ,
An optical inspection apparatus, comprising: an optical characteristic calculation unit that calculates optical characteristics of the subject based on a detection result of the optical sensor. An optical characteristic detection method for detecting an optical characteristic of a subject using the optical sensor according to any one of claims 1 to 12 ,
Determining a sensitivity distribution to the light of the subject,
Calculating an optical characteristic of the subject by solving an inverse problem based on the sensitivity distribution.