JP2006292513A - Refractive index distribution measuring method for refractive index distribution type lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method capable of measuring easily and quickly a refractive index distribution over the whole area of a rod lens. <P>SOLUTION: This refractive index distribution measuring method for a refractive index distribution type lens 12 is provided with a step for measuring an incident position into the first measuring face S3 separated from an S2 by a distance Z1 in every of the incident positions, while moving the incident position two-dimensionally from the first incident position on an S1 to the plurality of other incident positions, a step for measuring an incident position into the second measuring face S4 separated from the first measuring S3 by a distance Z2 in every of the incident positions, while moving the incident position two-dimensionally from the first incident position on the S1 to the plurality of other incident positions, a step for comparing the incident position into the first measuring face S3 with the incident position into the second measuring face S4 in every of the incident positions and for calculating an emission position and an emission angle from the emission end face S2, and a step for finding a refractive index distribution constant, based on the emission position and the emission angle of a light beam. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a refractive index distribution measuring method for a refractive index distribution type lens, and more particularly to a refractive index distribution type lens having a refractive index distribution in the radial direction, and more particularly to a method for measuring a refractive index distribution of a rod lens.

  The rod lens is used alone as a collimator lens in the transmission of optical information, and a rod lens array obtained by processing a large number of rod lenses into an array is a part of a line sensor used in a copying machine, a facsimile machine, a scanner, etc. Alternatively, it is widely used as a writing device for LED printers.

  As a refractive index distribution measurement method for evaluating the performance of a rod lens, for example, a method is known in which spherical aberration of a rod lens is measured and a refractive index distribution constant is calculated backward from the measurement result (Non-Patent Document). 1).

  FIG. 10 is a diagram for explaining a method of measuring the refractive index distribution of the rod lens 1 described in Non-Patent Document 1. In this method, a light bundle (incident light bundle) 4 that has passed through the condenser lens 2 is made incident at a position a distance a away from the central axis 6 of the rod lens 1 (object to be measured) to be measured. By measuring the positions a1 and a2 across the plane AA ′ and the plane BB ′ that are separated from the exit surface of the rod lens 1 by the distances L1 and L2, the trajectory of the light flux is obtained. Next, the incident position of the light beam 4 on the rod lens 1 is changed one-dimensionally, and the position where the trajectory of the light beam crosses the planes AA ′ and BB ′ is measured. In this manner, the spherical aberration of the rod lens 1 is obtained by repeating the operation for obtaining the locus of the light beam from the measurement result, and the refractive index distribution constant is calculated from the spherical aberration.

Also known is a method of calculating back the refractive index distribution constant from the curvature of field of the rod lens and the paraxial focal position (see Patent Document 1).
In this method, a pattern surface is set with the vicinity of one end face of a rod lens having a length P / 2 (P represents the meandering period length of light in the lens) as an object surface, and monochromatic light condensed on the pattern surface is collected. By irradiating, an image surface is formed in the vicinity of the other end surface, and this image surface is observed to obtain a paraxial focal position and a field curvature curve, and a back calculation is performed from these paraxial focal positions and a field curvature curve. Obtain the refractive index distribution constant.

"Aberration measurement and analysis of gradient index lens" Optics Vol. 6, No. 6, December 1982 JP 2002-243586 A

  However, in the method described in Non-Patent Document 1, since the incident position of the light beam is changed one-dimensionally within the incident end face of the rod lens, when measuring the refractive index distribution over the entire rod lens, It is necessary to repeat the work of positioning the lens.

  Further, in order to measure the positions a1 and a2 where the outgoing light beam 8 crosses the planes AA ′ and BB ′, the outgoing light beam 8 is received by a photosensor. For positioning, the outgoing light beam 8 is mounted on a fine movement stage. Since it is necessary to read the amount of movement of the fine movement stage with a dial gauge at a position where the light intensity of the photosensor reaches a peak while moving the slit through a detection slit (not shown), the measurement takes a very long time. It takes.

  On the other hand, in the method proposed in Patent Document 1, since a pattern surface is set as an object surface during measurement, complicated operations such as putting in and out of the pattern surface and position adjustment are required.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a method capable of easily and rapidly measuring the refractive index distribution of the entire rod lens.

  According to the present invention, based on the position of the light beam emitted from the light source and incident from one end face (incident end face) S1 of the gradient index lens and emitted from the other end face (exit end face) S2, the lens A refractive index distribution measuring method for a gradient index lens that measures the refractive index distribution of the light beam, wherein the incident position of the light beam is moved two-dimensionally from the first incident position on the S1 to a plurality of other incident positions. Measuring the incident position of the light beam on the first measurement surface S3 that is separated from the S2 by a distance Z1 for each incident position, and determining the incident position of the light beam from the first incident position on the S1. Measuring the incident position of the light beam on the second measurement surface S4 that is separated from the first measurement surface S3 by a distance Z2 for each of the incident positions while moving to other incident positions two-dimensionally; For each incident position, the first Comparing the incident position of the light beam on the fixed surface S3 with the incident position of the light beam on the second measurement surface S4, calculating the emission position and the emission angle of the light beam from the emission end surface S2, and And a step of obtaining a refractive index distribution constant based on the exit position and the exit angle. A method for measuring a refractive index distribution of a gradient index lens is provided.

  According to such a configuration, the incident position of the light beam on the incident end face of the lens can be moved two-dimensionally, so that the change in refractive index across the entire cross section of the lens can be measured quickly and easily.

  According to another preferred aspect of the present invention, the method further comprises a step of detecting an optical axis position of the lens, wherein the first incident position is the detected optical axis position.

  According to another preferred aspect of the present invention, the optical axis position detecting step measures the incident position P0 of the light beam incident on the first measurement surface S3 without passing through the lens from the light source, and the light source To measure the incident position P0 ′ of the light beam incident on the first measurement surface S3 through the lens, and move the lens so that the P0 ′ coincides with the P0, and the P0 ′ becomes the P0. And determining the incident position of the light beam on the S1 when it coincides with the optical axis position of the lens.

According to another preferred aspect of the present invention, the plurality of incident positions are arranged concentrically around the optical axis position of the lens.
According to another preferred aspect of the present invention, the plurality of incident positions are arranged on intersections of a lattice having the optical axis position of the lens as one intersection.

According to another preferred aspect of the present invention, the first incident position is a physical center position of the lens.
According to another preferred aspect of the present invention, the plurality of incident positions are arranged concentrically around the physical center position of the lens.
According to another preferred aspect of the present invention, the plurality of incident positions are arranged on intersections of a lattice having a physical center position of the lens as one intersection.

  ADVANTAGE OF THE INVENTION According to this invention, the method which can measure the refractive index distribution of the whole rod lens whole area simply and rapidly is provided.

Hereinafter, a rod lens refractive index distribution measuring method according to a preferred embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing a schematic configuration of a refractive index distribution measuring apparatus 10 that implements the rod lens refractive index distribution measuring method of the present embodiment, and FIG. 2 shows an incident end face S1 and an outgoing end face of a lens to be inspected. S2, the incident position P1 of the light beam on the first measurement surface S3, the second measurement surface S4, S1, the emission position P2 of the light beam from S2, the incident position P3 of the light beam on S3, and the incident position P4 of the light beam on S4 It is drawing which shows this relationship typically.

As shown in FIG. 1, the refractive index distribution measuring apparatus 10 includes a holder 14 that holds a rod lens 12 to be measured. The rod lens 12 and the holder 14 are mounted on a lens multi-axis stage 16 and configured to be movable. On the incident end side of the rod lens 12, a light source 18 that emits light for refractive index distribution measurement toward the incident end surface S <b> 1 of the rod lens 12, and an optical system disposed between the light source 18 and the rod lens 12 ( Lens group) 20 is arranged.
In the present embodiment, a laser light source such as a He—Ne laser is used as the light source 18. Further, the optical system 20 is configured to collect the light beam from the light source 18 on the incident end surface S <b> 1 of the rod lens 12.

  On the emission end side of the rod lens 12, a first CCD camera 22 that receives a light beam emitted from the emission end surface S <b> 2 of the rod lens 12 is mounted on the first multi-axis stage 24.

  A half mirror 26 is disposed between the lens group 20 and the rod lens 12 to deflect light from the end surface (incident end surface) S1 on the light source 18 side of the rod lens 12 by 90 degrees toward the side. Further, an image forming lens 28 that forms an image of the light deflected by the half mirror 26 and a second CCD camera 30 that picks up an image of the image forming lens 28 are disposed on the side of the half mirror 26. Yes. Therefore, the refractive index distribution measuring apparatus 10 of the present embodiment is configured such that the second CCD camera 30 can capture an image of the incident end surface S1 of the rod lens 12. The imaging lens 28 and the second CCD camera 30 are mounted on the second multi-axis stage 32 and configured to be movable.

  The first and second CCD cameras 22 and 30 are two-dimensional CCD cameras capable of detecting a two-dimensional position of a light beam. In the refractive index distribution measuring apparatus 10 of this embodiment, the output signals of the first and second CCD cameras 22 and 30 are sent to the personal computer 34, and the two-dimensional positions of the light beams received by the CCD cameras 22 and 30 are received. Is configured to be measurable.

  As shown in FIG. 1, in the refractive index distribution measuring apparatus 10 of this embodiment, the light source 18, the lens group 20, the rod lens 12, the first CCD camera 22, and the half mirror 26 are provided from the light source 18. The central axis is arranged on the same straight line (Z-axis) in the light emission direction. The second CCD camera 30 to which the imaging lens 28 is attached is disposed at a position deflected 90 degrees from the axis Z of the apparatus with the half mirror 26 as the center.

Next, a method for measuring the refractive index distribution of the rod lens 12 using the refractive index distribution measuring apparatus 10 will be described.
First, a rod lens 12 to be measured whose length is approximately P / 2 (P is the meandering period length of light in the lens) processed so that both end faces are substantially parallel is attached to the holder 14 and is measured. Deploy. At this time, the rod lens 12 is positioned so that the light beam L from the light source 18 enters the optical axis position on the incident end surface S1 of the rod lens 12. In the refractive index distribution measuring method of this embodiment, it is preferable to detect the optical axis position by the method described later.

  The first CCD camera 22 operates the first multi-axis stage 16 to emit from the exit end face of the rod lens 12 at the first measurement surface S3 that is separated from the exit end face S2 of the rod lens 12 by a distance Z1 in the Z-axis direction. It arrange | positions so that the light beam L which received may be received.

  Next, the light source 18 is operated, and the light beam L emitted from the light source 18 is incident on the optical axis position (first incident position) of the incident end surface S1 of the rod lens 12. The light beam L emitted from the emission end surface S2 of the rod lens 12 is received by the first measurement surface S3 by the first CCD camera 22, and the incident position P3 of the light beam L on the first measurement surface S3 is measured (FIG. 2).

  Next, while moving the incident position P1 of the light beam L to the rod lens 12 to a plurality of incident positions on the incident end surface S1, the light beam L emitted from the output end surface S2 of the rod lens 12 is changed to the first position for each incident position P1. The CCD camera 22 receives light on the first measurement surface S3, and measures the incident position P3 of the light beam L on the first measurement surface S3 for each incident position P1.

The movement of the incident position P1 is performed along a two-dimensional pattern that covers the entire area of the incident end face of the rod lens 12, for example, concentrically around the optical axis position that is the measurement start position. In this case, the other plurality of incident positions are concentrically centered around the measurement start position (optical axis position in the present embodiment) located at the center, as shown by a black circle in FIG. 3A, for example. Be placed.
Instead of concentric movement, movement along a lattice with the optical axis position as one intersection may be used. In this case, for example, as shown by a black circle in FIG. 3B, the other plurality of incident positions are gratings having a measurement start position (optical axis position in the present embodiment) located at the center as one intersection. It is arranged on the intersection of

  The change of the incident position P1 on the incident end surface S1 is performed by driving the lens multi-axis stage 16 and changing the position of the rod lens 12 so that the incident position P1 moves along a predetermined two-dimensional pattern. Is done. The driving of the lens multi-axis stage 16 is controlled by a personal computer 34.

  Next, as indicated by an arrow A in FIG. 2, the first CCD camera 22 is moved along the Z axis in a direction away from the rod lens 12 by the first multi-axis stage 24. It arrange | positions so that the light beam L radiate | emitted from the radiation | emission end surface of the rod lens 12 may be light-received in 2nd measurement surface S4 away from the 1st measurement surface S3 by the distance Z2.

  In this state, the same measurement as that performed by placing the first CCD camera 22 on the first measurement surface S3 is performed. That is, first, the light beam L is incident on the optical axis position on the incident end surface S1 of the rod lens 12 from the light source 18, and the light beam L emitted from the output end surface S2 of the rod lens 12 is second measured by the first CCD camera 22. The light is received by the surface S4, and the incident position of the light beam L on the second measurement surface S4 is P4 (FIG. 2).

Next, while the incident position P1 of the light beam L to the rod lens 12 is moved to a plurality of incident positions on the incident end face S1 along a two-dimensional pattern (for example, concentric), the emission of the rod lens 12 is performed for each incident position. The light beam L emitted from the end surface S2 is received by the first CCD camera 22 on the second measurement surface S4, and the incident position P4 of the light beam L on the second measurement surface S4 is measured for each incident position P1.
Here, each incident position on the incident end surface S1 is the same incident position as each incident position on the incident end surface S1 of the rod lens 12 when the incident position P3 of the light beam L on the first measurement surface S3 is measured. . Therefore, the incident positions P3 and P4 on the first measurement surface S3 and the second measurement surface S4 are measured for each incident position on the incident end surface S1 of the rod lens 12.

  The incident positions P3 and P4 on the measurement surface for each incident position P1 on the incident end face S1 thus measured are sent to the personal computer 34, and the light beam L is incident on the incident position P1 for each incident position P1 on the incident end face S1. The emission position P2 and the emission angle of the light beam L on the emission end face S2 are calculated. The calculated emission position P2 and emission angle for each incident position S1 are stored in the personal computer 34 as a data file.

  The incident position of the light beam L on the first measurement surface S3 and the second measurement surface S4 is detected by processing a spot image of the incident light beam captured by the first CCD camera 22 serving as the measurement surface by the personal computer 34. The spot image may be extracted by binarization processing with a predetermined threshold value, and the center of gravity of the extracted shape may be expressed in two-dimensional coordinates as the center position of the incident light beam.

  The refractive index distribution of the rod lens 12 can also be measured by observing the spot image, and the incident spot images of the light beams on the first measurement surface S3 and the second measurement surface S4 are stored in the personal computer 34 as an image file. May be.

ｎ₀:光軸上の屈折率
ｒ：光軸中心から半径方向の距離
ｇ、ｈ₄：屈折率分布定数
ｇおよびｈ₄の求め方は特に限定されないが、後述するような光学シミュレーションソフトを用いて求める方法が好ましい。 Based on the data of the exit position and exit angle on the exit end surface S2, the incident position on the first measurement surface S3, and the incidence position on the second measurement surface S4 obtained as a result of the measurement as described above, the lens 8 to be inspected. The refractive index distribution constants g and h ₄ are determined. The refractive index distribution of the rod lens can be approximated by the following equation.

n ₀ : Refractive index on the optical axis r: Distance g in the radial direction from the optical axis center, h ₄ : Refractive index distribution constant The method for obtaining g and h ₄ is not particularly limited, but optical simulation software as described later is used. This method is preferable.

As described above, since the incident position on the incident end face S1 of the rod lens 12 is moved two-dimensionally, the refractive index distribution of the entire cross section of the rod lens 12 is obtained. Therefore, a refractive index distribution along an arbitrary straight line (for example, a diameter) crossing the cross section of the rod lens 12 is also obtained.
Therefore, for example, when the refractive index distribution of the rod lens is not axially symmetric with respect to the optical axis position, a radial straight line passing through the optical axis is divided into two at the optical axis position, and along each divided straight line. The refractive index distribution can be obtained very easily.

  Next, detection of the optical axis position of the rod lens to be measured in the preferred embodiment of the present invention will be described. FIGS. 4A and 4B are diagrams for explaining this optical axis position detection method.

  This optical axis position detection method uses the refractive index distribution measuring apparatus 10. First, in a state where the rod lens 12 is not set on the holder 14, the light beam L emitted from the light source 18 is incident on the first measurement surface S3, and the incident position P0 of the light beam L on the first measurement surface S3 (FIG. 4 (a) )) Is measured. That is, the incident position P0 of the light beam L on the first measurement surface S3 in a state where the light beam L emitted from the light source 18 does not pass through the rod lens 12 is measured.

  Next, the rod lens 12 to be measured is set in the holder 14, and the light beam L from the light source 18 enters the incident end surface S 1 of the rod lens 12 and enters the first measurement surface S 3 when passing through the rod lens 12. The position P0 ′ (FIG. 4B) is measured.

  Furthermore, the incident position P0 ′ of the light beam L that has passed through the rod lens 12 to the first measurement surface S3 matches the incident position P0 of the light beam L that has not passed through the rod lens 12 to the first measurement surface S3. Then, the rod lens 12 is moved in the XY plane by the lens multi-axis stage 16. The incident position P1 of the light beam L on the incident end surface S1 of the rod lens 12 when the incident position P0 'coincides with the incident position P0 is defined as an optical axis position P1' of the rod lens 12.

  First, the optical axis position is detected as described above, and the state in which the incident position P0 ′ at the end of the optical axis position detecting process coincides with the incident position P0, that is, the optical axis position of the rod lens 12 It is preferable to start the above-described refractive index distribution measurement from the state where the light is incident on the light source.

In the movement of the rod lens 12 in the XY plane, the lens multi-axis stage 16 on which the holder 14 on which the rod lens 12 is set is mounted is controlled by a movement command signal from the personal computer 34.
Based on the output signal from the first CCD camera 22, the movement command signal passes through the rod lens 12 and the incident position P 0 of the light beam L that does not pass through the rod lens 12 in the personal computer 34 to the first measurement surface S 3. The difference of the position coordinates of the incident position P0 ′ of the incident light beam L on the first measurement surface S3 is calculated, and the lens multi-axis stage 16 is calculated to move in the direction in which the difference decreases.

  On the other hand, the first CCD camera 22 is moved to the second measurement surface S4 by moving the first CCD camera multi-axis stage 24, and the light flux that has passed through the rod lens 12 on the second measurement surface S4. The rod lens 12 is moved in the XY plane so that the position P0 ″ of L coincides with the position P0 of the light beam not passing through the rod lens 12, and the rod lens 12 of the light beam when P0 ″ coincides with the position P0. The incident position on the incident end face is set as the optical axis position P1 ″ of the rod lens 12, and this optical axis position P1 ″ is compared with the optical axis position P1 ′ determined based on the measurement on the first measurement surface S3. It may be confirmed that there is no deviation in the determined optical axis position. By doing so, it is possible to detect the optical axis position with higher accuracy.

  In the detection method of the incident position of the light beam on the first measurement surface S3, the spot image of the incident light beam captured by the CCD camera 22 which is the first measurement surface S3 is processed by the personal computer 34, and the spot image is processed with a predetermined threshold value. The position of the light beam is extracted by performing binarization processing in (2), and the center of gravity of the extracted shape is expressed in two-dimensional coordinates as the center position of the incident light beam. By using such a method, the center of the light beam can be specified even when the light spot system is expanded.

  When the optical axis position is detected using the incident position of the light beam L on the second measurement surface S4, the first multi-axis stage 24 on which the first CCD camera 22 is mounted is moved. The axis stage 24 is also controlled by a movement command signal from the personal computer 34 in the same manner as the lens multi-axis stage 16.

  After the position coordinates P0 of the light beam not passing through the rod lens 12 to the first measurement surface S3 and the position coordinates of the light beam L passing through the rod lens 12 to the first measurement surface S3 are coincident, the incident end surface In order to confirm the relationship between the optical axis position in S1 and the physical center position, an image of the incident end face S1 may be taken by the second CCD camera 30 capable of taking the incident end face S1 via the half mirror 26. .

  The image of the incident end face S1 is also processed by the personal computer 34, and the physical center position of the incident end face S1 is calculated. When a difference occurs between this physical center position and the optical axis position detected by the above-described method or the like, this difference becomes the amount of deviation of the optical axis of the rod lens 12.

  The second CCD camera 30 captures an image of the incident end surface S1 reflected and deflected by the half mirror 26 disposed on the light source 18 side of the rod lens 12, but the reflected light from the incident end surface S1 is sufficiently obtained. A reflector (not shown) may be disposed on the exit end face side of the rod lens 12. In such a configuration, the arrangement mechanism of the reflection plate is a sliding opening / closing mechanism, and the reflection plate may not be arranged on the emission end surface except when the incident end surface S1 is observed.

  In the refractive index distribution measuring method of the above embodiment, the first incident position of the incident end surface S1 of the rod lens is set as the optical axis center. However, when the optical axis position of the rod lens is shifted from the physical center position, etc. The first incident position may be the physical center position of the incident end surface S1 of the rod lens 12.

  Moreover, in the said embodiment, although the lens length of the rod lens 12 was set to P / 2 vicinity, you may select another lens length.

  Examples of the present invention will be described below. In this example, in order to confirm that the rod lens in which the optical axis deviation occurs can be measured, the manufacturing conditions are removed from the normal conditions, the refractive index distribution state is intentionally deteriorated, and the optical axis deviation occurs. A rod lens was used as a measurement target.

The specifications of the rod lens were an outer diameter of φ0.93 mm and a lens length of 5.60 mm. The rod lens has a meandering period length P at λ = 632.8 nm of 11.191 mm. The light source of the refractive index distribution measuring apparatus is a He—Ne laser (λ = 632.8 nm).
The measurement conditions were the optical axis position at which the measurement start position was detected, the movement pattern of the incident position was a lattice pattern, and the measurement interval was 20 μm. Further, the distance Z1 from the emission end surface S2 to the first measurement surface S3 was set to 16 mm, and the distance Z2 from the first measurement surface S3 to the second measurement surface S4 was set to 5 mm.

  FIG. 5 is a photograph of the incident end face S1 after detecting the optical axis position in this rod lens. As a result of the measurement, the deviation between the physical center of the lens to be inspected and the optical axis position was about 13.4 μm.

  FIG. 6A shows the result of plotting the incident position P3 on the first measurement surface S3, and FIG. 6B shows the result of plotting the incident position P4 on the second measurement surface S4. The results of using these measurement data in the optical simulation are shown below.

Based on the measured data, g and h ₄ shown in Equation 1 are calculated.
The optical simulation software used is ZEMAX (ZEMAX Development Corporation: USA).

In ZEMAX, the refractive index distribution can be expressed by inputting parameter values (n ₀ , n _r2 , n _r4 ) shown in Equation 2. Here, the relationship between g and h ₄ in Equation 1 is expressed by Equation 3.

From the measurement data, one-direction data in the radial direction is extracted from the measurement start position, fixed at h ₄ = 0, COSα at the exit end face S2 for the light flux closest to the center (data at a distance of 20 μm from the center), COSβ, COSγ (see FIG. 7), and g most fitting to the first position measurement surface S3 were obtained by using the OPTIMIZATION function of ZEMAX.

g is fixed to the value obtained above, h ₄ for each other data is obtained by the OPTIMIZATION function, the refractive index n (r) ² at each radius is calculated using Equation 2, and the graph shown in FIG. It was created. As shown in FIG. 9, an approximate polynomial of the refractive index n (r) ² with respect to the radius r ² was obtained, and n ₀ , n _r2 , and n _r4 were determined. Here, n ₀ ² = 2.2771, n _r2 = -0.7005, and n _r4 = 0.1366. Next, g and h ₄ were calculated from Equation 3, and values of g = 0.555 and h ₄ = 0.634 were obtained.
FIG. 9 shows a graph comparing the refractive index distribution in the central portion of the lens to be inspected obtained in this measurement with the refractive index distribution in the case of an ideal distribution lens.

  As described above, according to the present invention, the refractive index distribution constant can be obtained with high accuracy even in a rod lens in which an optical axis deviation occurs.

It is drawing which shows schematic structure of the refractive index distribution measuring apparatus which enforces the rod lens refractive index distribution measuring method of embodiment of this invention. Incidence end surface S1, exit end surface S2, first measurement surface S3, second measurement surfaces S4 and S1 of light beam incident position P1 and light beam exit position P2 and S3 of light beam incident positions P2 and S3 of the lens to be inspected It is drawing which shows typically the relationship between the incident position P4 of the light beam to P3 and S4. It is drawing which shows the movement pattern of the incident position at the time of a measurement. It is a surface explaining an optical axis position detection method. It is a photograph of incident end face S1 after detecting an optical axis position in a rod lens. (A) is a drawing showing the result of plotting the incident position P3 on the first measurement surface S3, and (b) is a drawing showing the result of plotting the incident position P4 on the second measurement surface S4. It is drawing which shows COS (alpha), COS (beta), COS (gamma), etc. in the output end surface S2. It is a graph which shows the refractive index n (r) 2 in each calculated radius. It is the graph which compared the refractive index distribution in the center part of the to-be-inspected lens obtained by this measurement, and the refractive index distribution in the case of an ideal distribution lens. It is a figure explaining the refractive index distribution measuring method of the rod lens of a prior art.

Explanation of symbols

S1: Incidence end surface S2: Emission end surface S3: First measurement surface S4: Second measurement surface P1: Incidence position on S1 P2: Emission position from S2 P3: Incident position of light flux on S3 P4: Flux of light flux on S4 Incident position 10: Refractive index distribution measuring device 12: Rod lens 16: Multi-axis stage for lens 18: Light source 22: First CCD camera 24: First multi-axis stage 26: Half mirror 30: Second CCD camera 32 : Second multi-axis stage 34: Personal computer (PC)

Claims (2)

The refractive index distribution of the lens is measured based on the position of the light beam emitted from one end face (incident end face) S1 of the gradient index lens and emitted from the other end face (exit end face) S2. A refractive index distribution measuring method for a gradient index lens,
While moving the incident position of the light beam two-dimensionally from the first incident position on the S1 to a plurality of other incident positions, for each incident position, to the first measurement surface S3 separated from the S2 by a distance Z1. Measuring the incident position of the luminous flux of
While the incident position of the light beam is moved two-dimensionally from the first incident position on the S1 to a plurality of other incident positions, for each incident position, a second distance Z2 away from the first measurement surface S3. Measuring the incident position of the light beam on the measurement surface S4;
For each incident position, the incident position of the light beam on the first measurement surface S3 and the incident position of the light beam on the second measurement surface S4 are compared, and the emission position and emission angle of the light beam from the emission end surface S2 are compared. Calculating steps,
Obtaining a refractive index distribution constant based on an exit position and an exit angle of the luminous flux,
A method for measuring a refractive index profile of a gradient index lens. Detecting the optical axis position of the lens further,
The first incident position is the detected optical axis position;
The refractive index distribution measuring method of the gradient index lens according to claim 1.

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