JP3292599B2 - Inspection method for gradient index lens array - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lens array of a gradient index lens array, in which parallel light or scattered light is incident, light emitted from each lens element is received, and the amount of light transmitted by each lens element alone. Alternatively, the present invention relates to an inspection method for determining a pass / fail by obtaining a 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 one or a plurality of stages to form one continuous image as a whole. It is a compound eye lens part. In such a refractive index distribution type lens array, the optical characteristics of the lens array change due to variations in the characteristics of each lens element (a slight difference in the refractive index distribution, etc.) or disorder in the arrangement of the lens elements. Therefore, the inspection of the gradient index lens array is performed by the following method. A method of arranging a test chart and a light receiving element so as to be equal to the distance between the object image planes actually used, placing a lens array at the center of the test chart, and measuring a response function (MTF; Modulation Transfer Function) of the lens array. . With the same arrangement as above, remove the test chart,
A method for measuring the amount of transmitted light and unevenness in the amount of light transmitted through a lens array when scattered light of uniform intensity is incident.

However, in such optical measurement, it is difficult to detect minute chipping (defects on the surface or a part close to the surface) and breakage (defects inside) of the lens element. Chipping of the lens element can occur when cutting into the lens array or polishing the end face of the lens array.Breaking of the lens element can occur when aligning and assembling the glass rods or at the end face of the lens array. This may occur when clamping is performed for polishing. Therefore, in addition to the above-described inspection by optical measurement, the external appearance of the lens array is visually observed to select a lens array having missing or broken lens elements.

[0004]

Although the above inspection methods can be automated, these inspection methods cannot completely detect defects of each lens element, and necessarily require a visual inspection. The reason is that the visual field radius of each lens element is usually 2 to 4 times the element diameter, and at the time of inspection, a composite image inspection of a plurality of lens elements is performed. This is because they are averaged due to the influence, and it is difficult to detect a defect of each lens element. In particular, in the inspection, even a normal lens element is affected by the presence of periodic light amount unevenness unique to a compound eye lens.

[0005] However, visual inspection is necessarily poor in reliability. It is easily influenced by the skill level and physical condition of workers, and certain standards cannot be observed. In particular, as the amount of work increases, oversight of defective products tends to increase. In addition, visual inspection cannot cope with a reduction in the lens element diameter. With the miniaturization of devices using the lens array, the size of the lens array tends to be further reduced, and the lens element diameter is becoming smaller (for example, about 0.6 mm or less). Then, the defect is not visible to the naked eye, and the inspection using a microscope or the like has problems such as tired eyes, which is inefficient. Further, in the visual inspection, it is difficult to distinguish between a defect having a problem in practice and a defect having no problem, so that selection at a level considered to be more severe than necessary is required. For example, in the case of a chip, for example, the size, position, shape, depth, and condition of the fractured surface vary widely, and it is not possible to set a limit that has or does not affect the optical performance.

An object of the present invention is to provide a method of inspecting a gradient index lens array that can detect chipping or breakage of each lens element without relying on visual inspection.
Another object of the present invention is to cope with a reduction in the diameter of a lens element,
An object of the present invention is to provide a method of inspecting a gradient index lens array which has high reliability, can set a clear quality judgment criterion, 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 affected by light emitted from an adjacent lens element. This is a method of inspecting a gradient index lens array in which the transmitted light amount or the light amount distribution of each lens element alone is obtained by receiving light while eliminating the light, and comparing non-defective products with non-defective products by comparing with a predetermined quality judgment criterion. . Here, as the parallel light, a parallel light having an intensity distribution rotationally symmetric about the optical axis is used . Specifically, the laser light is once made incident on the single mode fiber, and the emitted light is made into parallel light using a collimator lens.

[0008] In the case of a one-stage arrangement type gradient index lens array, scattered light can be used instead of parallel light. In that case, scattered light is incident on each lens element, and the emitted light is received by eliminating 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, The transmitted light amount or light amount distribution of each lens element alone is obtained, and compared with a predetermined quality judgment criterion.
Sort out 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,
What is necessary is just to scan the slit in the width direction of the lens array relatively to the lens array.

[0010]

When light is incident from the end face of the lens array, only one light path is determined by the incident position and the incident angle of the light beam, and only one emission position and the emission angle are determined. Conversely, if the emission position and the emission angle are determined, only one incident position and the incident angle are 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 enters, the outgoing light propagates while converging slightly. When scattered light is incident, a range of light rays within a range that can be received by a sufficiently small light receiving element at an arbitrary distance from the emission surface can be limited in terms of the incident position and the incident angle. Normally, the side of each lens element of the gradient index lens array is subjected to flare cut processing, so that incident light from outside the ray capturing range of the lens element is diffusely reflected and absorbed on the side of the lens, and reaches the exit surface. Cannot be reached. Therefore, if the light receiving position is appropriately selected, it is possible to scan the lens array in the width direction and detect the light amount distribution of each lens element alone while receiving almost no light emitted from the adjacent lens element.

If the lens element has a defect (chip or break), the light beam is blocked, refracted, or scattered. In these cases, since the light path deviates from the normal state, the optical performance of the lens array is naturally affected, and the degree can be expressed as a difference in the light amount distribution of the lens elements. As a result, the presence / absence and degree of a defect for each lens element can be detected.

[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 index rod lenses) 12 arranged so as to form one continuous image as a whole. This is a compound eye lens part. In the present invention, parallel light or scattered light enters from one end face of the lens array 10 and light emitted from the other end face is received. At this time, the light receiving position is selected according to the properties of the incident light and the structure of the lens array, and the light emitted from each lens element is received while eliminating the influence of the light emitted from the adjacent lens element. As a result, the transmitted light amount or light amount distribution of each lens element alone is obtained, and a non-defective / defective product is selected by comparing with a preset pass / fail judgment criterion.

When parallel light is incident, the light is emitted 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 enters, the outgoing light propagates while converging slightly. As shown in FIG. 2A, when the lens element 12 is arranged in one step, the light receiving position is within a range (indicated by a chain line) of twice the focal length from the end face of the lens element 12. , Anywhere. As shown in FIG. 2B, when the lens elements 12 are arranged in two stages, if the light is received at a position between the line XX and the line YY, the upper lens element 12a and the lower lens element Excluding the mutual influence of 12b, the light transmitted through each lens element can be measured.

For example, when the calculation is performed assuming the size and position of a chip as shown in FIG. 3, the following is obtained. The missing part is indicated by oblique lines. The size of the chip is 1 of the lens diameter.
3, the missing position is the 9 o'clock position on the clock face in the example on the left side of FIG. 3, and the 6 o'clock position in the example on the right side. FIG. 4 shows the calculation result of the emitted light amount distribution in the case where the parallel light having a uniform intensity distribution is incident and there is a defect-free product and there is a chip and the light is blocked. The horizontal axis is the detection position with the emitted light beam radius being 1.0, and the vertical axis is the detected light amount (relative value). If the lens element is chipped and the light beam is cut off, the light beam path deviates from the normal state (in the case of the defect-free lens element), so that a difference in the light amount distribution appears.

When the lens elements are arranged in a single stage, scattered light can be used. When the scattered light enters the lens element 12, the emitted light becomes 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 (from the exit surface to the lens diameter D).
It can be seen that if the light is received at a position that is slightly shorter distance), the light amount distribution of each lens element alone can be detected. Assuming the size and position of the chipping as shown in FIG. 3, FIG. 6 shows the calculation results of the emission light amount distribution for a defect-free product when scattered light is made incident and for a case where there is a chipping and the light is blocked. The horizontal axis is the detection position with the emitted light beam radius being 1.0, and the vertical axis is the detected light amount (relative value). If the lens element is defective and the light beam is blocked, the light beam path deviates from the normal state (in the case of a non-defective lens element), resulting in a difference in light amount distribution.

The light beam capturing range of the gradient index lens element becomes narrower as it approaches the periphery of the lens. Therefore, the parallel light beam where all the incident light is emitted and the scattered light incident beam where the light beam not captured due to the incident angle increases. In this case, the detected light amount distribution shape is different. 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 parallel light is used, it is actually difficult to obtain a 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 therefrom is collimated by the collimator lens 24.
It is desirable to make them parallel using. Lens array 10
Light emitted from the photodiode 2 through a slit 26 formed in the thickness direction of the lens array.
The light is received at 8, amplified by an amplifier 30 and processed by a personal computer 32. The lens array 10 is mounted on a moving stage 34, and the lens array is moved in the width direction (the direction indicated by the arrow), and the light amount distribution is sequentially obtained for each lens element 12.

FIG. 9 shows an aperture angle of about 12 ° (NA of about 0.1 mm).
2) Parallel light having an axially symmetrical intensity distribution is made incident on a refractive index distribution type lens array having a lens element diameter of 0.6 mm, and this is used at a position 0.5 mm from the exit surface using a slit having a width of 0.2 mm. The light quantity distribution detected and received by the photodiode is detected as a defect-free product or a defective product (as shown in FIG. 8, when the incident surface has a chip of 1/5 of the lens diameter at the 2 o'clock position). )
These are the results measured for The horizontal axis is the distance from the reference position of the lens array. In addition, according to the result of the optical measurement, the MTF was 77.2% (6
Lp / mm), and the light amount unevenness was 6.2%, all of which were judged to be non-defective by the conventional inspection standard. According to the inspection method of the present invention, such chipping can be sufficiently detected. In addition, the method of the present invention can also detect a pitch shift of a lens element and the like.

In the present invention, the incident light may be white light, but it is preferable to use monochromatic light because lens elements generally have chromatic aberration. As described above, the light source may be a parallel light source or a scattered light source. However, when the lens array is of a two-stage type, a parallel light source is used. Scattered light sources are readily available, but are 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 tends to be high.In the case of a distribution having no symmetry, the effect 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 an intensity distribution that is rotationally symmetric about the optical axis.

As a light receiving method, there is a method of receiving light with a photodiode, a photomultiplier, or the like through a slit formed in a direction perpendicular to the scanning direction. Alternatively, a method of receiving light at one or more pinholes or end faces of optical fibers may be used.

The inspection items include an integrated value and a peak value of the detected light amount distribution curve, a light amount value at a specific position, a shift of an optical axis position, and the like. It is also conceivable to compare the shape of the light intensity distribution curve itself, and the IAE (Integrated Absolute Error) and ISE (In
integrated Squared Error) may be used as the evaluation value. The comparison target is a predetermined target shape, a peripheral lens obtained by a moving average method (for example, a method of averaging several front and rear parts, a method of sampling several front and rear parts and taking an average except for a maximum value and a minimum value). The average value of the elements, the average value of all the lens elements constituting the lens array, and the like can be considered. As a method of calculating the optical axis position, a peak value position, a position at which the area is equally divided, a tangent to a distribution curve at an appropriate light amount position, and a position where the distribution curve intersects may be considered.
The inspection results are different between the case where the defect is on the incident surface and the case where the defect is on the output surface. Therefore, it is preferable to perform the inspection from both directions as necessary.

[0022]

According to the present invention, the performance and characteristics of each lens element of the lens array can be accurately grasped only by managing the light source and the light receiving element. I can do it. By selecting an appropriate slit width on the light receiving side, it is possible to cope with a lens element having a small lens diameter that is difficult to observe with the naked eye. In addition, since the transmitted light amount of each lens element itself is inspected, it is possible to distinguish between those that have an effect on optical performance and those that do not affect the optical performance, and the results can be output as numerical values for each inspection item. Can be set.

[Brief description of the drawings]

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

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

FIG. 3 is an explanatory view 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 view of a light path when scattered light is incident.

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

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

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

FIG. 9 is a graph showing actually measured values of the distribution of the amount of emitted light when parallel light enters a defect-free product and a defective product.

[Explanation of symbols]

 Reference Signs List 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

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-56-120933 (JP, A) JP-A-5-149824 (JP, A) JP-A-56-635 (JP, A) JP-A 57-120 3027 (JP, A) JP-A-4-190131 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01M 11/00-11/08 G01N 21/84-21/958

Claims (5)

(57) [Claims] 1. A parallel light having an intensity distribution rotationally symmetric about an optical axis is incident on each lens element of a gradient index lens array, and light emitted from each lens element is emitted from an adjacent lens element. Refractive index distribution characterized by finding the transmitted light amount or light amount distribution of each lens element alone by receiving the light while eliminating the influence of the emitted light, and comparing non-defective / defective products with a preset pass / fail judgment criterion. Method for inspecting lens arrays. 2. A collimated light incident on the lens elements, once the laser beam is incident on a single-mode fiber, the method of claim 1, wherein is obtained by a parallel light using a collimator lens and the exit light. 3. The 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 moved relative to the lens array in the width direction of the lens array. 3. The method according to claim 1, wherein scanning is performed. 4. An adjacent lens in which scattered light is incident on each lens element of a one-stage array type gradient index lens array, and the emitted light is disposed at a position sufficiently close to an emission surface. The refraction is characterized by receiving the light while eliminating the influence of the light emitted from the element, finding the transmitted light amount or light amount distribution of each lens element alone, and comparing it with a preset quality judgment criterion to select non-defective / defective products. Inspection method of rate distribution type lens array. 5. 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 in the width direction of the lens array relative to the lens array. The method of claim 4 .