JP4360526B2 - Hologram observation tool and computer generated hologram therefor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hologram observation tool and a computer generated hologram therefor, and more particularly, to a hologram hologram that is easy to make and has a bright and stable image viewed through the hologram glasses and a computer generated hologram therefor.
[0002]
[Prior art]
In Patent Document 1, hologram glasses are proposed. The hologram glasses are configured as shown in a perspective view in FIG. That is, two transmission holograms 2 and 3 are fitted into the binocular frame of the spectacle frame 1. When a scene including light sources 4, 5, 6, and 7 having a small area as shown in FIG. 7B is viewed by wearing glasses using the transmission holograms 2 and 3, for example, as shown in FIG. 7C. Looks like. That is, the light sources 4, 5, 6, and 7 in the actual scene of FIG. 7B are seen as scenes that have been replaced with the previously selected patterns “NOEL” 8, 9, 10, and 11, respectively. As the transmission holograms 2 and 3 having such characteristics, a Fourier transform hologram (Fraunhofer hologram) having the pattern “NOEL” configured as a computer generated hologram is used.
[Patent Document 1]
US Pat. No. 5,546,198 [Non-Patent Document 1]
Textbook "Holograms and diffractive optical elements-from basic theory to industrial application" sponsored by The Optical Society of Japan (Applied Physics Society) pp. 36-39
[0003]
[Problems to be solved by the invention]
A Fourier transform hologram obtained by a computer corresponds to a cell position by dividing a limited rectangular area including a pattern ("NOEL" in the above example) recorded in the hologram into a grid-like cell vertically and horizontally. Each cell is provided with information on the pattern portion, and a pattern consisting of a limited number of cells is projected by Fourier transform onto a distant hologram area. In fact, the hologram area is also recorded. Similar to the pattern area, it is divided into cells in a grid pattern in the vertical and horizontal directions, and the amplitude information and phase information of each cell position subjected to Fourier transform of the pattern to be recorded are recorded.
[0004]
As described above, a Fourier transform computer generated hologram in which a preselected pattern is recorded is composed of a finite number of cells. Therefore, the diffraction efficiency is not necessarily high, and the pattern seen through the hologram glasses is not necessarily bright. Further, the conjugate image appears to overlap the pattern, and further, a high-order diffraction image is seen close to the periphery of the main pattern, so that it cannot be said that it is easy to see and has sufficient characteristics.
[0005]
In addition, for the production of such a computer generated hologram, a photolithographic technique using a mask produced by fast Fourier transform is used. However, since the drawing pattern of the mask is very fine, a predetermined pattern can be stably formed. It is not easy to produce a computer generated hologram that reproduces.
[0006]
The present invention has been made in view of such problems of the prior art, and its purpose is to produce a high-diffraction-efficient, bright pattern that replaces the light source in the scene, resulting in a conjugate image and a higher-order image. Another object of the present invention is to provide a hologram observation tool and a computer generated hologram therefor that can be easily manufactured with predetermined characteristics.
[0007]
[Means for Solving the Problems]
The hologram observation tool of the present invention that achieves the above object is a hologram observation tool that is configured as a transmission type Fourier transform hologram and includes a computer generated hologram. The computer generated hologram includes a pitch δ _{x of} a minute cell that forms the computer generated hologram. , Δ _y , 2δ _x , 2δ _y , and a diffraction grating having a lattice interval of ± 1st order diffracted light of a predetermined wavelength defined by the range sandwiched by ± 1st order diffracted light within a range of 1/2 or less of the reproduced image region It is characterized in that an original picture pattern reproduced at a wavelength is recorded.
[0009]
In this case, the computer generated hologram is preferably a phase hologram.
[0010]
Further, it is desirable that the phase distribution of the computer generated hologram is multivalued in four or more stages.
[0011]
The computer generated hologram of the present invention is configured as a transmission type Fourier transform hologram for an observation tool. In the computer generated hologram for a hologram observation tool, the pitches δ _x and δ _y of the minute cells constituting the computer hologram are two times 2δ _x. An original pattern reproduced at the wavelength within a range of 1/2 or less of the reproduced image area of the computer generated hologram defined by the range sandwiched by the ± 1st order diffracted light of the predetermined wavelength of the diffraction grating having a grating interval of 2δ _y It is characterized by being recorded.
[0013]
In this case, the computer generated hologram is preferably a phase hologram.
[0014]
Moreover, it is desirable that the phase distribution is multi-valued in four or more stages.
[0015]
In the present invention, the definition is made within a range sandwiched between ± 1st order diffracted lights of a predetermined wavelength of a diffraction grating having a grating interval of 2δ _x , 2δ _y , which is twice the pitch δ _x and δ _y of a minute cell constituting a computer generated hologram. Since the original image pattern reproduced at that wavelength is recorded in the range of 1/2 or less of the reconstructed image area of the computer hologram to be viewed, a bright, conjugated image and a high-order image inconspicuous pattern can be seen through the observation tool. Thus, a Fourier transform hologram composed of a computer generated hologram for a hologram observation tool that can be easily replaced with a light source in a scene and that has a predetermined characteristic can be easily obtained.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the hologram observation tool of the present invention and a computer generated hologram therefor will be described.
[0017]
FIG. 1 schematically shows a computer generated hologram 20 (corresponding to the transmission holograms 2 and 3 in FIG. 7A) fitted in the frame of the hologram glasses of the present invention and an image region 30 reproduced therefrom. Computer-generated hologram 20 is the Fourier transform hologram, made of an aggregate of size [delta] _y, the horizontal direction (x-axis direction) dimension [delta] _x of the small cell 21 in the longitudinal direction arranged in a grid pattern (y-axis direction) In this embodiment, as will be described later, each cell 21 has only phase information. 2 ^m cells 21 are arranged in the x-axis direction and 2 ⁿ cells are arranged in the y-axis direction.
[0018]
On the other hand, the image region 30 arranged sufficiently far from the computer generated hologram 20 is a set of cells 31 arranged in the same 2 ^m pieces in the x-axis direction and the same 2 ⁿ pieces in the y-axis direction corresponding to the computer generated hologram 20. Each cell 31 has a vertical direction (y-axis direction) dimension Δ _y and a horizontal direction (x-axis direction) dimension Δ _x , and the length of the entire image region 30 in the x-axis direction is L _x and the length in the y-axis direction. it is is a L _y.
[0019]
The x-axis direction length L _x and the y-axis direction length L _y of the image region 30 are related to the x-axis direction dimension δ _x and the y-axis direction dimension δ _y of the cell 21 of the computer generated hologram 20, respectively. When expressed by the diffraction angle from the computer generated hologram 20 (since the image region 30 is located far away from the computer generated hologram 20, it is better to express L _x and L _y as angles), L _x is the spatial frequency 1 / corresponds to ± 1 range sandwiched by order diffracted light of the diffraction grating (2δ _x), L _y corresponds to a range sandwiched by ± 1-order diffracted light of the diffraction grating spatial frequency 1 / (2δ _y). This corresponds to the fact that the maximum spatial frequency recorded in the computer generated hologram 20 is 1 / (2δ _x ) in the x-axis direction and 1 / (2δ _y ) in the y-axis direction.
[0020]
With this arrangement relationship, when parallel light 15 having a predetermined wavelength is incident from the front of the computer generated hologram 20, diffracted light 16 is generated on the back side of the computer generated hologram 20, and the pattern recorded on the computer generated hologram 20 in the distant image region 30. For example, the letter “F” as described below is reproduced. Accordingly, when such a computer generated hologram 20 is used in place of the glasses lens and the front direction of the computer generated hologram 20 is viewed, the letter “F” can be seen. Therefore, for example, when a scene as shown in FIG. 7B is viewed through the computer generated hologram 20, it appears as a scene in which the light sources 4, 5, 6, and 7 are replaced with the pattern “F”.
[0021]
An embodiment will be described in which the phase information of each cell 21 is calculated and obtained so that the computer generated hologram 20 reproduces the pattern “F”. In this method, in order to give predetermined diffracted light to the reproduced image plane, a computer generated hologram is arranged on the hologram plane while alternately repeating Fourier transform and inverse Fourier transform while applying a constraint condition between the reproduced image plane and the hologram plane. This is a method known as Gerchberg-Saxton iterative calculation (for example, Non-Patent Document 1).
[0022]
Here, for easy understanding, the amplitude distribution (pixel value) of the original image on the reproduced image plane 30 is A _IMG (x, y), and the phase distribution of the original image on the reproduced image plane 30 is φ _IMG (x, y,). The amplitude distribution on the hologram surface 20 is A _HOLO (u, v), and the phase distribution on the hologram surface 20 is φ _HOLO (u, v). As shown in FIG. 2, in step (1), the pixel value of the original image to be recorded is given as A _IMG (x, y) in the reproduction image plane 30 region, and the phase distribution of the original image is initialized to a random value. In step (2), the initialized value is subjected to Fourier transform. In step (3), the amplitude distribution A _HOLO (u, v) on the hologram surface 20 obtained by Fourier transform is set to 1, and the phase distribution φ _HOLO (u, v) is multi-valued (quantized) in a predetermined manner. A binding condition is given. After such a constraint condition is given, in step (4), inverse Fourier transform is performed on the amplitude distribution A _HOLO (u, v) and the phase distribution φ _HOLO to which the constraint condition is given. If it is determined in step (5) that the amplitude distribution A _IMG (x, y) on the reproduced image plane 30 obtained by the inverse Fourier transform is substantially equal to the pixel value of the original image, the convergence is determined in step (3). The multilevel (quantized) phase distribution φ _HOLO (u, v) is the phase distribution given to the cell 21 of the computer _generated hologram 20. If it is determined in the convergence determination in step (5) that the amplitude distribution A _IMG (x, y) obtained by the inverse Fourier transform is not equal to the pixel value of the original image, in the inverse Fourier transform in step (6). Instead of the obtained amplitude distribution A _IMG (x, y), a pixel condition of the original image is given, and a constraint condition is given to leave the phase distribution φ _IMG (x, y) obtained by inverse Fourier transform as it is. After such a binding condition is given, the loop of step (2) → (3) → (4) → (5) → (6) is satisfied until the condition of step (5) is satisfied (until convergence). Repeatedly, the final desired computer generated hologram 20 is obtained.
[0023]
In addition, the process of multi- _{leveling the} phase distribution φ _HOLO (u, v) is not performed in step (3), and a predetermined multi-level process is performed after the condition of step (5) is satisfied. Also good.
[0024]
The depth distribution of the actual hologram is obtained from the multi-valued phase distribution φ _HOLO (u, v) obtained in this way. In the case of a transmission type like the present invention, the following equation (1) is obtained. Based on this, the depth is converted to the depth D (x, y) of the computer generated hologram 20.
[0025]
D (u, v) = λφ _HOLO (u, v) / {2π (n ₁ −n ₀ )} (1) where λ is the center wavelength used, and n ₁ and n ₀ are transmission holograms. It is the refractive index of the two materials which comprise. Then, as illustrated in the cross-sectional view of FIG. 3, by forming a relief pattern 18 having a depth of D (u, v) obtained by the above formula (1) on the surface of the transparent substrate 17, the computer of the present invention. A hologram 20 is obtained. In the case of FIG. 3, φ _HOLO (u, v) is an example of multi-leveling in four stages of 0, π / 2, π, and 3π / 2. The coordinates (u, v) on the hologram surface 20 are for distinction from the coordinates (x, y) on the reproduced image plane 30. As the direction of the coordinate axis, the u-axis direction is the x-axis. Direction, the v-axis direction corresponds to the y-axis direction.
[0026]
By the way, as described above, the computer generated hologram 20 according to the present invention can reproduce an arbitrary pattern having an arbitrary size within the range of the x-axis direction length L _x and the y-axis direction length L _y of the image region 30. However, if the size of the reproduced pattern is too large within the vertical and horizontal dimensions L _y × L _x , several problems occur.
[0027]
The first is that if the size of the reproduction pattern occupied in the image region 30 is relatively large, the number of levels of multi-values in the computer generated hologram 20 decreases. As described above, since there is a Fourier transform relationship between the surface of the computer generated hologram 20 and the surface of the reproduced image region 30, in order to record the pattern reproduced in the entire reproduced image region 30 on the computer generated hologram 20, It is necessary to record at the maximum spatial frequency 1 / (2δ _x ) (x-axis direction) and 1 / (2δ _y ) (y-axis direction) that can be recorded on the computer generated hologram 20, and the phase distribution of the computer generated hologram 20 is recorded. The number of multi-value levels must be two stages, that is, two stages of 0 and π. However, when the number of multi-value levels is two, the diffraction efficiency is only 40.5% at the maximum, so a pattern reproduced over the entire image area 30 that can be theoretically reproduced by such a computer generated hologram 20 is obtained. When recording is attempted, the brightness of the reproduced image must be dark, and bright conjugate images are reproduced in an inline manner, making it difficult to see the original pattern.
[0028]
Here, in order to record in the computer generated hologram 20 so that the pattern is reproduced not within the entire reproduced image region 30 but within a range 35 of both vertical and horizontal directions as shown in FIG. 1 / (3δ _x ), 1 / (3δ _y ) must be recorded. Therefore, the number of multilevel levels of the phase distribution to be recorded is three stages, that is, 0, 2π / 3, 4π / 3, and the diffraction efficiency is increased to 68.4% at the maximum, so that a brighter reproduced image can be obtained. Then, the conjugate image that is reproduced by overlapping in-line gets in the way.
[0029]
Therefore, when recording is made on the computer generated hologram 20 so that the pattern is reproduced within a range 35 that is ½ both vertically and horizontally as shown in FIG. The number of multi-value levels is four, that is, 0, π / 2, π, 3π / 2, and the diffraction efficiency is 81.1% at the maximum. With such a high diffraction efficiency, the brightness of the reconstructed image is sufficient, and the conjugate image reconstructed in-line is hardly noticeable.
[0030]
The second problem is a higher-order image reproduced around the reproduced image area 30. The computer generated hologram 20 has cells 21 having an x-axis direction dimension δ _x and a y-axis direction dimension δ _y arranged in a grid pattern, a diffraction grating having a lattice interval δ _{x in} the x-axis direction, and a grating in the y-axis direction. This is the same as the diffraction grating with the interval δ _y superimposed on the phase distribution φ _HOLO (u, v). Therefore, ± 1st-order unwanted diffracted light is generated with the diffraction grating having a grating interval δx in the _x- axis direction as a carrier (carrier wave) and the diffraction grating having a grating interval δy in the _y- axis direction as a carrier (carrier wave). As shown in FIG. 5, the original reproduced image “F” is generated in an area around the original pattern “F” in which the carrier is reproduced in the reproduced image area 30 and adjacent to the reproduced image area 30. Four higher order images “F” of the same pattern are reproduced. In FIG. 5A, the pattern “F” is reproduced within a range of 1/2 or less in both the vertical and horizontal directions of the reproduced image area 30 (a rectangular area where black vertical bars and black horizontal bars intersect). 5 (b) shows that the reproduction image area 30 (a rectangular area where the black vertical bar and the black horizontal bar intersect) is within a range of 2/3 or more in both vertical and horizontal directions. Shows an image reproduced when the pattern “F” is recorded so as to be reproduced.
[0031]
As is clear from comparison between FIGS. 5A and 5B, when a pattern reproduced on the entire reproduction image region 30 is recorded on the computer generated hologram 20, the reproduction image is obtained as shown in FIG. The higher order image reproduced around the original pattern “F” reproduced in the region 30 is too close and unnoticeable, which is not desirable. On the other hand, when a pattern reproduced in the range of 1/2 or less in both the vertical and horizontal directions of the reproduced image area 30 is recorded in the computer generated hologram 20, it is reproduced in the reproduced image area 30 as shown in FIG. Higher order images reproduced around the original pattern “F” are relatively distant and are not so noticeable and unobtrusive.
[0032]
The third problem relates to a photomask when the multi-valued phase distribution φ _HOLO (u, v) of the computer generated hologram 20 is produced using a photolithography technique. FIG. 6 shows two photomasks when the original _images shown in (a1) and (a2) are recorded as four-level multi-valued Fourier transform holograms having only the phase distribution φ _HOLO (u, v). (B1) and (b2) are photomask patterns for applying phase modulation π, and (c1) and (c2) are photomask patterns for applying phase modulation π / 2, respectively. In this example, it is divided into 32 in both vertical and horizontal directions. The original image in FIG. 6 (a1) is an original image pattern that is reproduced within a range of 1/2 or less in both the vertical and horizontal directions of the reproduced image area 30, and FIG. 6 (a2) is reproduced in a range exceeding 1/2 in both the vertical and horizontal directions. Original pattern.
[0033]
The phase distribution is multi-valued in four stages using a photomask ((b1), (b2)) that provides phase modulation π and a photomask ((c1), (c2)) that provides phase modulation π / 2. For example, when performing pattern exposure twice and etching the transparent substrate 17 using a positive resist, an opening of a phase modulation π photomask and an opening of a phase modulation π / 2 photomask And a phase portion of 3π / 2 is obtained, and exposure is performed so that the opening of the phase modulation π photomask and the light shielding portion of the phase modulation π / 2 photomask overlap. The phase portion of π / 2 is obtained by exposing the light shielding portion of the photomask with phase modulation π and the opening portion of the photomask with phase modulation π / 2 to overlap, and the phase portion of π / 2 is obtained. Photomask shading part and phase modulation / By 2 of the light-shielding portion of the photomask is exposed so as to overlap so that the phase of 0 is obtained.
[0034]
As is clear from comparison of FIGS. 6 (a1) to (c1) and (a2) to (c2), in the case of (a2) to (c2), as indicated by arrows in (b2). An isolated pattern is likely to occur in a photomask for producing the computer generated hologram 20. On the other hand, in the cases (a1) to (c1), such an isolated pattern hardly occurs. When such an isolated pattern exists in the photomask, the corner of the isolated pattern is rounded during drawing or transferring, and the pattern reproducibility of the computer generated hologram 20 using the same is deteriorated or noise light is increased. Such problems arise.
[0035]
As described above, when viewed from any of the first to third points, the diffraction grating having a lattice spacing of 2δ _x , 2δ _y , twice the pitch δ _x , δ _y of the minute cell 21 of the computer generated hologram 20. An original image pattern reproduced within a range of 2/3 or less, preferably 1/2 or less, of a reconstructed image area 30 of the computer generated hologram 20 defined by a range sandwiched by ± first-order diffracted light is recorded on the computer generated hologram 20. By doing so, a bright, conjugate image, and a pattern with inconspicuous higher-order images can be seen by replacing the light source in the scene that is viewed through the glasses, and it is easy to produce a hologram with predetermined characteristics. A Fourier transform hologram comprising a hologram is obtained.
[0036]
The hologram glasses according to the present invention and the computer generated holograms therefor have been described based on the embodiments. However, the present invention is not limited to these, and various modifications are possible. In addition, the computer generated hologram of the present invention includes use for hologram glasses for one eye, and can be used not only for hologram glasses but also for windows or displays.
[0037]
【The invention's effect】
As is clear from the above description, according to the hologram observation tool of the present invention and the computer generated hologram therefor, the lattice spacing of 2δ _x , 2δ _y , which is twice the pitches δ _x and δ _y of the minute cells constituting the computer hologram, is obtained. Since the original pattern reproduced at that wavelength is recorded in the range of 1/2 or less of the reproduced image area of the computer generated hologram defined by the range sandwiched by the ± 1st order diffracted light of the predetermined wavelength of the diffraction grating possessed, it is bright Consists of computer-generated holograms for holographic observation tools, in which a conspicuous image or a high-order image is inconspicuous, can be replaced with a light source in a scene viewed through the observation tool, and can be easily manufactured with a predetermined characteristic A Fourier transform hologram is obtained.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing a computer generated hologram fitted in a frame of hologram glasses of the present invention and an image area reproduced therefrom.
FIG. 2 is a flowchart for obtaining a computer generated hologram of the present invention.
FIG. 3 is a cross-sectional view showing a configuration example of a computer generated hologram according to the present invention.
FIG. 4 is a diagram illustrating an example of a pattern reproduction range in a reproduction image area.
FIG. 5 is a diagram showing an original reproduction pattern reproduced in a reproduction image area and four higher-order images around it.
FIG. 6 is a diagram showing an original picture and a photomask pattern for applying phase modulation corresponding to the original picture pattern.
FIG. 7 is a diagram for explaining hologram glasses and their operation.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Glasses frame 2, 3 ... Transmission hologram 4, 5, 6, 7 ... Small area light source 8, 9, 10, 11 ... Preselected replacement pattern 15 ... Parallel light 16 ... Diffraction light 17 ... Transparent substrate 18 ... Relief pattern 20 ... Computer generated hologram (hologram surface)
21 ... Cell 30 ... Image area (reproduced image plane)
31 ... cell 35 ... pattern reproduction range

Claims (6)

In a hologram observing tool configured as a transmission type Fourier transform hologram and comprising a computer generated hologram, the computer generated hologram includes a lattice of 2δ _x and 2δ _{y which is} twice the pitch δ _x and δ _y of the minute cells constituting the computer generated hologram. The original pattern to be reproduced at that wavelength is recorded within a range of ½ or less of the reproduced image area of the computer generated hologram defined by the range sandwiched by the ± 1st order diffracted light of the predetermined wavelength of the diffraction grating having the interval. Hologram observation tool characterized by. It said computer hologram, a hologram viewing device according to claim 1, characterized in that it consists of a phase hologram. The hologram observation tool according to claim 2, wherein the phase distribution of the computer generated hologram is multi-valued into four or more levels. In a computer generated hologram for a holographic observing tool configured as a transmission type Fourier transform hologram for an observing tool, the pitch of δ _x , δ _y of the minute cells constituting the computer generated hologram is set to 2δ _x , 2δ _y. The original pattern reproduced at the wavelength is recorded in a range of 1/2 or less of the reproduced image area of the computer generated hologram defined by the range sandwiched by the ± 1st order diffracted light of the predetermined wavelength of the diffraction grating. A computer generated hologram. 5. The computer generated hologram according to claim 4, comprising a phase hologram. 6. The computer generated hologram according to claim 5, wherein the phase distribution is multi-valued in four or more stages.

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