JPH0815090A - Method for inspecting distributed index lens array - Google Patents

Abstract

PURPOSE:To cope with a reduction in diameter of lens elements, to set a highly reliable definite defectless/defective discriminating criterion, and to perform inspections with high reproducibility by detecting the chipping, breaking, etc., of each lens element without relying on visual inspections. CONSTITUTION:The light quantity transmitted by or the light quantity distribution of each lens element 12 of a distributed index lens array 10 is found by making parallel or scattered light incident on each element 12 and receiving the light emitted from each element 12 by eliminating the influence of the light emitted from adjacent elements 12 and defectless lens arrays are sorted from defective lens arrays by comparing the found light quantity transmitted by or the light quantity distribution of each lens element with a preset defectless/ defective discriminating criterion. Such parallel light that has an intensity distribution rotationally symmetrical with respect to the optical axis is preferable as the parallel light made incident on each element 12. At the time of finding the light quantity distribution, the light emitted from each element 12 is received by means of a photoreceptor element through a slit which is moved against the lens array in the width direction of the array.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a case where parallel light or scattered light is incident on each lens element of a gradient index lens array, light emitted from each lens element is received, and the amount of transmitted light of each lens element alone is received. Alternatively, the present invention relates to an inspection method for determining the quality by obtaining the light amount distribution.

[0002]

2. Description of the Related Art In a gradient index lens array, a large number of minute rod-shaped lens elements (gradient index rod lenses) are arranged in a single stage or a plurality of stages to form one continuous image as a whole. It is a compound eye lens component. In such a gradient index lens array, the optical characteristics of the lens array change due to variations in the characteristics of each lens element (such as a slight difference in the refractive index distribution) or disorder of the array of lens elements. Therefore, the gradient index lens array is inspected by the following method. A method to measure the response function (MTF; Modulation Transfer Function) of the lens array by arranging the test chart and the light receiving element so that the distance between the image planes of the object actually used is arranged and the lens array is installed at the center position. . With the same arrangement as above, remove the test chart,
A method for measuring the amount of transmitted light and unevenness of light amount of a lens array when scattered light of uniform intensity is incident.

However, it is difficult to detect minute defects (defects on the surface or a portion close to the surface) and breaks (defects inside) of the lens element by such optical measurement. The chipping of the lens element can occur when cutting into the lens array or when polishing the end surface of the lens array, and the breakage of the lens element occurs when the glass rods are aligned and assembled or the end surface of the lens array. It may occur when clamped for polishing. Therefore, in addition to the above-described inspection by optical measurement, the appearance of the lens array is visually observed to select a lens array having a missing or broken lens element.

[0004]

Although the above inspection methods and the above inspection methods can be automated, these inspection methods cannot detect the defects of each lens element one by one, and thus require visual inspection. The reason is that the visual field radius of each lens element is usually 2 to 4 times the element diameter, and in the inspection of and, since it is a combined image inspection of a plurality of lens elements, the images of the adjacent lens elements are This is because the influence is averaged and it is difficult to detect defects in each lens element. Especially in the inspection, the presence of the periodic light amount unevenness peculiar to the compound eye lens affects even a normal lens element.

However, visual inspection is by no means reliable. It is easily influenced by the skill level and physical condition of the operator, and certain standards cannot be observed. In particular, as the amount of work increases, there is a tendency for missed defective products to increase. Further, the visual inspection cannot cope with the reduction of the lens element diameter. Along with the downsizing of devices using the lens array, the lens array tends to be downsized, and the lens element diameter is also small (for example, about 0.6 mm or less). Then, the defect is not visible to the naked eye, and the examination using a microscope has problems such as eye fatigue, which is inefficient. Further, in visual inspection, it is difficult to distinguish a defect having a problem in practical use from a defect having no problem in practical use, so that it is inevitable to perform selection at a level considered to be more severe than necessary. For example, in the case of a chip, the size, the position, the shape, the depth, the state of the fracture surface, and the like are inconsistent, and it is not possible to set limits for those with or without affecting the optical performance.

An object of the present invention is to provide a method for inspecting a gradient index lens array capable of detecting chipping or bending of each lens element without relying on visual inspection.
Another object of the present invention is to cope with a reduction in diameter of a lens element,
An object of the present invention is to provide a method for inspecting a gradient index lens array, which has high reliability, can set a clear quality judgment standard, and can perform inspection with good reproducibility.

[0007]

According to the present invention, parallel light is made incident on each lens element of a gradient index lens array and light emitted from each lens element is influenced by light emitted from an adjacent lens element. It is a method of inspecting a gradient index lens array that determines the transmitted light amount or light amount distribution of each lens element alone by removing the light and compares it with a preset acceptance criterion to select good products and defective products. . Here, the parallel light is preferably parallel light having a rotationally symmetrical intensity distribution around the optical axis. Specifically, the laser light is once incident on the single mode fiber, and the emitted light is collimated using a collimator lens.

In the case of the one-stage array type gradient index lens array, scattered light may be used instead of parallel light. In that case, to each lens element, the scattered light is incident, and the emitted light is received by removing the influence of the emitted light from the adjacent lens element by disposing the light receiving element at a position sufficiently close to the emission surface, Obtain the transmitted light quantity or light quantity distribution of each lens element independently, and compare it with the preset acceptance / rejection criteria.
Select defective products.

To obtain the light quantity distribution, light is received by a light receiving element through a slit formed in the thickness direction of the lens array,
The slits may be scanned relative to the lens array in the width direction of the lens array.

[0010]

When the light is incident from the end face of the lens array, only one optical path is determined by the incident position and the incident angle of the light beam, and the exit position and the exit angle are also determined by one. On the contrary, if the emission position and the emission angle are obtained, only one of the incident position and the incident angle is determined. The lens length of each lens element in the gradient index lens array is set to be slightly longer than half the meandering period P of the light beam. Therefore, when parallel light is incident, the emitted light propagates while being slightly converged. When the scattered light is incident, the light ray in a range that can be received by a sufficiently small light receiving element placed at an arbitrary distance from the emission surface can limit the range of the incident position and the incident angle. Normally, the flare cut process is applied to each lens element side surface of the gradient index lens array, so incident light from outside the ray trapping range of the lens element is diffusely reflected and absorbed by the lens side surface on the way to the exit surface. Can't reach Therefore, if the light receiving position is appropriately selected, it is possible to scan the lens array in the width direction and to detect the light amount distribution of each lens element alone with almost no light emitted from the adjacent lens elements.

If the lens element has a defect (a chip or a break), the light beam is blocked, refracted or scattered. In these cases, the light path is deviated from the normal state, which naturally affects the optical performance of the lens array, and the degree thereof can be expressed as the difference in the light amount distribution of the lens elements. This makes it possible to detect whether or not there is a defect in each lens element.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a gradient index lens array 10 has a large number of minute lens elements (gradient gradient rod lenses) 12 arranged so as to form one continuous image as a whole. It is a compound eye lens component. In the present invention, parallel light or scattered light is made incident from one end face of the lens array 10 and light emitted from the other end face is received. At that time, the light receiving position is selected according to the property of the incident light and the structure of the lens array, and the light emitted from each lens element is received without the influence of the light emitted from the adjacent lens element. In this way, the transmitted light quantity or light quantity distribution of each lens element is obtained and compared with a preset acceptance / rejection criterion to select good / defective products.

When parallel light is incident, it becomes emitted light as shown in FIG. The lens length of each lens element in the gradient index lens array is set to be slightly longer than half the meandering period P of the light beam. Therefore, when parallel light is incident, the emitted light propagates while being slightly converged. As shown in A of FIG. 2, when the lens elements 12 are arranged in one stage, if the light receiving position is within a range from the end surface of the lens element 12 to a position twice the focal length thereof (shown by a chain line). , Anywhere As shown in FIG. 2B, when the lens elements 12 are arranged in two layers, if the light is received at a position between the X-X line and the Y-Y line, the upper lens element 12a and the lower lens element 12a. Except for the mutual influence of 12b, the light transmitted through each lens element can be measured.

For example, assuming the size and position of the chip as shown in FIG. 3, the calculation is as follows. The chipped portion is indicated by diagonal lines. The size of the chip is 1 of the lens diameter.
The position of the chipping is / 5, and in the example on the left side of FIG. 3, it is the 9 o'clock position on the dial of the timepiece, and on the right side it is the 6 o'clock position. FIG. 4 shows the calculation result of the emitted light quantity distribution in the case of a defect-free product when a parallel light having a uniform intensity distribution is made incident and when there is a chip and a light beam is blocked. The abscissa represents the detection position with the emitted light ray radius being 1.0, and the ordinate represents the detected light amount (relative value). If the lens element is chipped and the light ray is blocked, the light ray path deviates from the normal state (in the case of a defect-free lens element), and this results in a difference in the light amount distribution.

When the lens elements are arranged in a single stage, scattered light can also be used. When scattered light is incident on the lens element 12, the emitted light is as shown in FIG. The shaded area is the range affected by the light emitted from the adjacent lens element. In this example, the central aperture angle is 12 °, and the position is close to the exit surface (lens diameter D from the exit surface).
It can be seen that the light amount distribution of each lens element alone can be detected by receiving light at a position slightly separated by a slightly shorter distance. FIG. 6 shows the calculation result of the emitted light amount distribution for a defect-free product when scattered light is incident and for a case where there is a chip and the light is blocked, assuming the size and position of the chip as shown in FIG. The abscissa represents the detection position with the emitted light ray radius being 1.0, and the ordinate represents the detected light amount (relative value). When a lens element has a defect and blocks a light beam, the light path is deviated from the normal state (in the case of a defect-free lens element), which results in a difference in light amount distribution.

The light trapping range of the gradient index lens element becomes narrower as it gets closer to the periphery of the lens. Therefore, in the case of parallel light in which all the incident light is emitted, and in the scattered light incidence where the number of light rays not trapped increases depending on the incident angle. The detected light amount distribution shape is different from that in the case. However, it can be seen that a clear difference occurs in the emitted light amount distribution when there is a chip, regardless of whether parallel light or scattered light is used.

When using parallel light, it is actually difficult to obtain parallel light having a uniform intensity distribution. Therefore, it is necessary to use parallel light having a symmetrical intensity distribution shape around the optical axis. Therefore, as shown in FIG. 7, the laser light from the laser oscillator 20 is once made incident on the single mode fiber 22, and the light emitted from the single mode fiber 22 is collimated by the collimator lens 24.
It is desirable to make them parallel by using. Lens array 10
Light emitted from the photo diode 2 is a light receiving element through a slit 26 formed in the thickness direction of the lens array.
The light is received at 8, amplified by the amplifier 30, and processed by the personal computer 32. The lens array 10 is mounted on the moving stage 34, and the lens array is moved in the width direction (the direction indicated by the arrow) to sequentially obtain the light amount distribution for each lens element 12.

FIG. 9 shows an opening angle of about 12 ° (NA about 0.
2) Make parallel light with an axially symmetric intensity distribution enter a gradient index lens array with a lens element diameter of 0.6 mm, and use a slit with a width of 0.2 mm at a position 0.5 mm from the exit surface. The light amount distribution detected by the photodiode is detected and the light amount distribution detected by the photodiode is compared with that of the defect-free product and the defect product (as shown in FIG. )
It is the result of measuring about. The horizontal axis is the distance from the reference position of the lens array. It is to be noted that this defect is 77.2% (6
Lp / mm), and the light amount unevenness is 6.2%, which are all judged to be non-defective products by the conventional inspection standard. According to the inspection method of the present invention, such a chip can be sufficiently detected. In addition to this, the method of the present invention can detect a pitch shift of the lens element.

In the present invention, the incident light may be white light, but since the lens element generally has chromatic aberration, it is preferable to use monochromatic light. The light source may be a parallel light source as described above, or a scattering light source. However, when the lens array is a two-stage stack type, a parallel light source is used. Scattered light sources are readily available, but slightly affected by adjacent lens elements. When a parallel light source is used, the influence of adjacent lens elements can be eliminated, but the intensity distribution of incident light is easy to occur, and in the case of a distribution without symmetry, the influence of the light source is likely to be reflected in the inspection result depending on the light receiving position. As described above, it is desirable to have a rotationally symmetrical intensity distribution around the optical axis.

As a light receiving method, there is a method of receiving light with a photodiode, a photomultiplier tube or the like through a slit formed in a direction perpendicular to the scanning direction. Alternatively, a method of receiving light through a pinhole or a plurality of points, an end face of an optical fiber or the like may be used.

The inspection items include the integrated value of the detected light amount distribution curve, the peak value, the light amount value at a specific position, the shift of the optical axis position, and the like. It is also possible to compare the shapes of the light amount distribution curves themselves, and IAE (Integrated Absolute Error), ISE (In
You may use integrated squared error) etc. as an evaluation value. The target of comparison is a target shape determined in advance, a peripheral average lens obtained by a moving average method (for example, a method of taking an average of several before and after, a method of sampling several before and after and taking the average excluding the maximum and minimum values) The average value of the elements, the average value of all lens elements forming the lens array, and the like can be considered. The optical axis position may be calculated as a peak value position, a position where the area is equally divided, a tangent line to the distribution curve at an appropriate light amount position, and a position where the tangent lines intersect.
Since the inspection result differs depending on whether the defect is on the incident surface or the emission surface, it is preferable to inspect from both directions as necessary.

[0022]

According to the present invention, since the performance and characteristics of each lens element of the lens array can be accurately grasped by simply managing the light source and the light receiving element, human factors can be eliminated and a highly reproducible inspection can be performed. You can do it. By selecting an appropriate slit width on the light receiving side, it is possible to deal with a lens element having a small lens diameter that is difficult to observe with the naked eye. Also, because the amount of transmitted light of each lens element itself is inspected, it is possible to distinguish between those that do not affect optical performance and those that do not affect optical performance, and it is possible to output the result as a numerical value for each inspection item, so there is a clear acceptance criterion. Can be set.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a method of the present invention.

FIG. 2 is an explanatory diagram of a ray path when parallel light is incident.

FIG. 3 is an explanatory diagram showing an example of a defect of a lens element.

FIG. 4 is a graph showing a calculated value of an emitted light amount distribution when parallel light is incident.

FIG. 5 is an explanatory diagram of a ray path when scattered light is incident.

FIG. 6 is a graph showing a calculated value of an outgoing light amount distribution when scattered light is incident.

FIG. 7 is an explanatory diagram showing an example of an inspection device used in the method of the present invention.

FIG. 8 is an explanatory diagram showing an example of a defect of a lens element.

FIG. 9 is a graph showing measured values of emitted light amount distributions of a defect-free product and a defect product when parallel light is incident.

[Explanation of symbols]

 10 Lens Array 12 Lens Element 20 Laser Oscillator 22 Single Mode Fiber 24 Collimator Lens 26 Slit 28 Photodiode 30 Amplifier 32 Personal Computer 34 Moving Stage

Claims (6)

[Claims] 1. A parallel light is made incident on each lens element of a gradient index lens array, and light emitted from each lens element is received by eliminating influence of light emitted from an adjacent lens element. A method for inspecting a gradient index lens array, characterized in that a transmitted light amount or a light amount distribution of each lens element is obtained, and a non-defective product or a defective product is selected by comparing with a preset quality determination standard. 2. The method according to claim 1, wherein the parallel light incident on the lens element is a parallel light having a rotationally symmetrical intensity distribution around the optical axis. 3. The method according to claim 2, wherein the collimated light incident on the lens element is laser light which is once incident on a single mode fiber, and the emitted light is collimated by using a collimator lens. 4. Light emitted from each lens element is received by a light receiving element through a slit formed in the thickness direction of the lens array, and the light source and the slit are relatively arranged in the width direction of the lens array with respect to the lens array. 4. The method according to claim 1, wherein scanning is performed. 5. A lens adjacent to a lens element of a graded index type lens array of one-stage array type in which scattered light is made incident and light emitted is arranged at a position sufficiently close to an emission surface. Refraction characterized by eliminating the influence of the light emitted from the element, receiving the light, obtaining the transmitted light amount or light amount distribution of each lens element alone, and comparing it with the preset acceptance criteria to select good products and defective products Inspection method of rate distribution type lens array. 6. Light emitted from each lens element is received by a light receiving element through a slit formed in the thickness direction of the lens array, and the slit is scanned relative to the lens array in the width direction of the lens array. The method of claim 5.