JP2000275142A - Method and apparatus for measurement of double refraction - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a double-refraction measuring method which is hardly influenced by a noise such as a stain or the like on the surface of an object to be inspected and which can measure the double refraction of the object to be inspected. SOLUTION: This double-refraction measuring method finds the double refraction of an object 1 to be inspected on the basis of both pieces of polarization information, i.e., polarization information on the transmitted light of the object to be inspected, which is found by a change in a light intensity obtained in such a way that the object 1 to be inspected is irradiated with nearly circularly polarized light, that a luminous flux transmitted through the object to be inspected is received by a light receiving means 9 only via an analyzer 7, and that the analyzer 7 is turned and polarization information on the transmitted light of the object to be inspected, which is found on the basis of a change in a light intensity obtained in such a way that the luminous flux transmitted through the object 1 to be inspected is received by the light receiving means 9 via a phase shifter 17 and the analyzer 7, and that the analyzer 7 is turned.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a birefringence measuring method for measuring the birefringence of a test object which is a plastic product such as a plastic lens used for optical writing or pickup used in a laser printer or the like. Regarding the device.

[0002]

2. Description of the Related Art Hitherto, a phase modulation method and a rotary analyzer method have been known as a method for measuring birefringence of a test object such as a test lens of this type. In these methods, a transparent test object is irradiated with a thin parallel beam, the transmitted light from the test object is received by a light-receiving element such as a photodiode, and the transmitted light is polarized by the birefringence of the test object. By detecting a change in the state, the birefringence of the test object is obtained.

In the phase modulation method, the "optical technology contact" V
ol.27.No.3 (1989), `` Measurement and Application of Birefringence by Phase Modulation Method '', p.127-p.134, etc.
The irradiation light is phase-modulated using a photoelastic modulator (PEM), and the birefringence is obtained from the phase of the beat signal and the modulation signal of the light transmitted through the transparent test object.

In the rotation analyzer method, "Optical Measurement Handbook" (published on July 25, 1981), edited by Toshiharu Tada, Junpei Tsujiuchi, Shigeo Minami, "Analysis of Polarization" in Asakura Shoten, p.256-p.265, etc. As described in, the transmitted light is received by the light receiving element on the back of the analyzer while rotating the analyzer placed on the back of the transparent test object, and the received light output from the light receiving element with the rotation of the analyzer The birefringence is determined by the change in.

Further, according to JP-A-4-58138, JP-A-7-77490, etc., a parallel test object is irradiated with expanded parallel light, and the transmitted light is transmitted to a two-dimensional sensor such as a CCD camera. The birefringence of the test object is determined by receiving the light at, and surface measurement of the birefringence is enabled.

[0006]

In both the phase modulation method and the rotating polarizer method, so-called "point measurement" in which, for example, a thin parallel beam is irradiated on an object and received by a photodiode.
Therefore, it is necessary to adjust the test object and the measuring device to measure the entire surface of the test object. Particularly, when a non-flat plate such as a lens is used as the test object, Since the irradiated light beam is refracted by the test lens, setting of the test object and the measuring device is complicated and difficult.

According to Japanese Patent Application Laid-Open No. 4-58138, since it is a "surface measurement", it is not necessary to adjust a test object or the like, but a writing plastic lens (usually used for a laser printer or the like) is usually used. In the case of a measurement object such as an fθ lens, which generally has a high NA, a large diameter, and is axisymmetric, there is a large difference in the degree of refraction depending on the location, and transmitted light is blurred or overlapped, and a transmitted image is distorted. Therefore, it is difficult to obtain a clear transmission image over the entire surface of the lens, and it is difficult to perform accurate measurement over the entire surface.

Further, in these measurement methods, the measurement range is limited by the wavelength of the light source used in the measurement. Therefore, when the thickness of the test object is large, uncertainty due to the light source wavelength is not obtained in the measured value obtained. There is a defect that is included. As a specific proposal example, for example, according to Japanese Patent Application Laid-Open No. 4-58138, an expanded parallel light is irradiated on a transparent test object, and the transmitted light is received by a two-dimensional sensor such as a CCD camera. Thus, the birefringence of the test object is determined, but the measurement result of the birefringence is 0 to λ
Since it is obtained within the range of / 4 (λ: light source wavelength), the measurement result of the birefringence phase difference exceeding the range is uncertain. That is, when the measured value of the birefringence phase difference is δ and the true birefringence phase difference is δ ′, the following relationship holds: δ ′ = m · λ / 2 ± δ (m: integer). Indeterminate. After all, in the example of JP-A-4-58138, the measurement range is determined by the light source wavelength λ, so that it is not possible to cope with large birefringence beyond the measurement range, and when the birefringence distribution exceeds the measurement range. Also cannot respond. In particular, plastic lenses for optical writing systems used in laser printers and the like may have a small-diameter plastic lens or a birefringence and a birefringence distribution that is thicker than an optical disc and exceeds the measurement range determined by the light source wavelength. It is thought enough. For this reason, the birefringence measurement method is required to be capable of measuring a large birefringence without being restricted by the wavelength of the light source.

Accordingly, an object of the present invention is to provide a birefringence measuring method and a birefringence measuring method capable of performing favorable birefringence measurement which is hardly affected by noise such as dirt on the surface of a test object.

Another object of the present invention is to provide a birefringence measuring apparatus capable of performing birefringence measurement in a short time and with high spatial resolution by using a light receiving element array having a plurality of light receiving elements arranged in parallel. And

When the test object has a curvature like a lens, the way of refraction of the light passing through the test object differs depending on the location. Therefore, a complicated configuration is required to guide all the transmitted light to the light receiving element. The present invention has a problem that the operability is poor and it takes time, so even if the test object has a curvature like a lens, it is simple, short, and with high spatial resolution. An object of the present invention is to provide a birefringence measurement device capable of performing highly accurate measurement.

When the object to be inspected is a lens, the focal length varies depending on the type. In the case of a non-axisymmetric lens, there are situations where the focal lengths differ in the orthogonal direction.
An object of the present invention is to provide a birefringence measuring device capable of improving versatility with respect to such a change in the type of the lens to be inspected.

In addition, another object of the present invention is to provide a birefringence measuring apparatus capable of improving the operability of the apparatus by automatically changing the setting of the position and arrangement.

Further, when the area of the test object is large, if it is desired to simultaneously receive the light flux transmitted through the entire surface of the test object, it is necessary to optically reduce the transmitted image, and the spatial space of the measurement must be reduced. Resolution drops. If the transmitted light of the test object is to be received at once without optically reducing the transmitted image, a large area polarizing element and a light receiving element are required, which causes a problem that the cost is increased. And to provide a birefringence measurement method and apparatus capable of performing measurement with high spatial resolution.

In addition, the present invention provides a birefringence measuring method and apparatus capable of measuring with high spatial resolution over the entire surface of a test object even when the test object is a lens having a short focal length. The purpose is to provide.

Similarly, the present invention provides a birefringence measuring method capable of measuring with high spatial resolution over the entire surface of an object even when the object is a parallel plate or a lens having a long focal length. It is intended to provide the device. together,
It is an object of the present invention to reduce the size of the apparatus when measuring a lens whose test object has a long focal length.

In order to achieve the above object, when performing a split measurement, if the surface of the test object has irregularities (depth) in the direction of the optical axis of the optical system, the surface of the test object and the light receiving element may differ depending on the location. The image formation relationship is not established and the image is blurred, which may cause a problem that accurate birefringence information cannot be obtained.However, even in such a situation, the present invention does not cover the entire surface of the test object. It is an object of the present invention to provide a birefringence measuring method and an apparatus thereof capable of performing accurate measurement.

The measurement range is limited by the wavelength of the light source used, and the measurement result of the phase difference of a large birefringence exceeding the measurement range includes a problem that uncertainty due to the wavelength of the light source is included. An object of the present invention is to provide a birefringence measuring method and an apparatus thereof that can obtain a wide (infinite) measuring range that is not limited by the light source wavelength.

Further, in realizing the above object, if the change in the birefringence of the test object in the test region is large, a two-dimensional light-dark distribution (photoelasticity) formed by the transmitted light flux of the test object is obtained. The interval between bright portions of the interference fringe) or the interval between dark portions (interference fringe interval) becomes narrower, and the interval becomes smaller than the size of a single light receiving element, so that the measurement range cannot be expanded accurately. However, the present invention provides a method and apparatus for measuring a birefringence capable of expanding a measurement range even when a change in birefringence of a test object is large in a test area. The purpose is to provide.

In order to achieve the above object, when obtaining a wide measurement range which is not limited by the wavelength of the light source, it takes a long time to perform the processing and may cause a processing error. The measurement range from 4 to + λ / 4 is-
The process of expanding from λ / 2 to + λ / 2 can be performed in a short time and
An object of the present invention is to provide a birefringence measuring method and an apparatus thereof that can be realized without processing errors completely.

Further, in the birefringence measuring apparatus for realizing the above-mentioned object, the change in the birefringence phase difference at an arbitrary position with respect to the measured value of the birefringence phase difference at a position set as a reference in the two-dimensional area to be inspected ( Phase difference distribution) is obtained as a two-dimensional spatial distribution. In other words, it is a comparative measurement with respect to the birefringence measurement value at the reference position. Therefore, since the measured value of the birefringence phase difference at the reference position may already exceed the measurement range determined by the wavelength of the light source used, the value measured by the birefringence measurement device is the absolute value of the birefringence phase difference. Not necessarily. Therefore, the present invention measures or estimates the absolute value of the birefringence phase difference at a position set as a reference in the test space, and combines it with the measurement result of the two-dimensional spatial distribution to obtain the entire test region. An object of the present invention is to provide a method and an apparatus for measuring birefringence, which can determine the absolute value of the birefringence phase difference.

Further, attention is paid to the fact that the optical writing system is often constituted by a plurality of lenses in actual use, and the present invention provides the above-described measurement method even when they are assembled as an optical system. It is an object of the present invention to provide a birefringence measuring device capable of responding to the following.

[0023]

According to a first aspect of the present invention, there is provided a method for measuring birefringence, comprising irradiating a test object with substantially circularly polarized light.
The light flux transmitted through the test object is received by the light receiving means only through the analyzer, and the polarization information of the test object transmitted light obtained from the change in light intensity obtained when the analyzer is rotated; The polarization information of the transmitted light of the specimen, which is received by the light receiving means via the phase shifter and the analyzer through the phase shifter and the analyzer, and the light intensity change obtained when the analyzer is rotated. The birefringence of the test object is determined based on both pieces of polarization information. The invention according to claim 2 is a method for measuring birefringence according to claim 1,
By moving the phase shifter in a direction other than the optical axis of the optical system, a state where the phase shifter is interposed and a state where the phase shifter is not interposed in the optical path from the test object to the light receiving unit are generated. .

According to a ninth aspect of the present invention, there is provided a birefringence measuring apparatus, comprising: a light source for irradiating the test object with substantially circularly polarized light; and a polarization of transmitted light transmitted through the test object. A phase shifter for changing a state, an analyzer for detecting a polarization state of light transmitted through the phase shifter, a light receiving unit for receiving light transmitted through the analyzer, and a light receiving unit for receiving the light from the object. A phase shifter advance / retreat switching means for generating a state in which the phase shifter is interposed on the optical path to the means and a state in which the phase shifter is not interposed; a rotating means for rotating the analyzer around its optical axis; Rotation angle detection means for detecting a rotation angle of the analyzer, holding means for holding the object, and a light reception output detected by the light reception means and a rotation angle detected by the rotation angle detection means Calculate the birefringence of the test object based on It includes a calculation means.

Therefore, according to the first, second and ninth aspects of the present invention, it becomes possible to measure the birefringence which is hardly affected by noise such as dirt on the surface of the test object.

According to a third aspect of the present invention, in the birefringence measuring method according to the first or second aspect, the test area of the test object is divided into a plurality of areas in a plane perpendicular to the optical axis of the optical system. And measurement data on polarization information. Therefore, the test area is divided into a plurality of areas in a plane perpendicular to the optical axis of the optical system, and the light transmitted through the test object in each area is received, thereby achieving high spatial resolution over the entire test object. Measurement of birefringence is possible.

According to a fourth aspect of the present invention, there is provided the birefringence measuring method according to the first or second aspect, wherein the imaging relation between the surface of the object and the light receiving surface of the light receiving means is always maintained. The test area of the object was divided into a plurality of areas in a plane perpendicular to the optical axis of the optical system, and measurement data on polarization information was obtained. Therefore, while always maintaining the image forming relationship between the surface of the test object and the light receiving surface of the light receiving means, the test area is divided into a plurality of areas in a plane perpendicular to the optical system optical axis, and the object area in each area is divided. By receiving the transmitted light beam of the specimen, even if the surface of the specimen has irregularities in the optical axis direction of the optical system, over the entire surface of the specimen,
It is possible to measure birefringence with high spatial resolution.

According to a fifth aspect of the present invention, in the birefringence measuring method according to the first or second aspect, the light-receiving means is a light-receiving element array comprising a plurality of light-receiving elements, and each of the adjacent light-receiving elements has The difference between the measured birefringence phase differences was detected, and when the difference was close to a predetermined amount, the difference was corrected to expand the measurement range of the calculated birefringence phase difference. Accordingly, a wide (infinite) wide measurement range not limited to the light source wavelength can be obtained.

According to a sixth aspect of the present invention, in the birefringence measuring method according to the first or second aspect, a major axis direction of the elliptically polarized light transmitted through the phase shifter is detected, and based on the information of the major axis direction, The measurement range of the calculated birefringence phase difference was expanded. Therefore, the process of extending the measurement range -λ / 4 to + λ / 4 to -λ / 2 to + λ / 2 in the birefringence measurement method according to the first aspect can be performed in a short time and accurately.

According to a seventh aspect of the present invention, in the birefringence measuring method according to the first or second aspect, the light receiving means is a light receiving element array composed of a plurality of light receiving elements, and the length of the elliptically polarized light transmitted through the phase shifter. After detecting the axial direction and expanding the measurement range of the calculated birefringence phase difference based on the information of the long axis direction, between the adjacent light receiving elements of the light receiving element array, the measured birefringence phase difference of each is measured. By detecting the difference and correcting the difference when the difference is close to a predetermined amount, the measurement range of the calculated birefringence phase difference is expanded.
Therefore, a wide (infinite) measurement range that is not limited by the light source wavelength can be obtained more accurately.

According to an eighth aspect of the present invention, in the birefringence measurement method according to the first or second aspect, the absolute amount of the birefringence phase difference at a reference position within an arbitrarily set test area is estimated and estimated. The absolute amount of the birefringence phase difference was applied to all the measured values of the measured two-dimensional spatial distribution of the birefringence phase difference, and the absolute amount of the birefringence phase difference in the entire test region was measured. Therefore, the absolute value of the birefringence phase difference in the entire two-dimensional test area can be determined.

According to a tenth aspect of the present invention, in the birefringence measuring apparatus of the ninth aspect, the light receiving means comprises a light receiving element array in which a plurality of light receiving elements are arranged in parallel. Accordingly, birefringence measurement can be performed in a short time and with high spatial resolution.

According to an eleventh aspect of the present invention, in the birefringence measuring apparatus according to the tenth aspect, there is provided an irradiation optical system for always making a light flux of transmitted light transmitted through the test object substantially parallel to an optical axis. An imaging optical system for forming an image of the light transmitted through the test object on a light receiving surface of the light receiving element array. Therefore, even when the test object has a curvature like a lens, simple, short-time, high spatial resolution and high-precision measurement can be performed.

According to a twelfth aspect of the present invention, in the birefringence measuring apparatus of the eleventh aspect, the irradiation optical system comprises a plurality of optical systems that can be freely combined. Therefore, the versatility with respect to the change of the type of the test lens can be improved.

According to a thirteenth aspect of the present invention, in the birefringence measuring apparatus according to the eleventh or twelfth aspect, a moving means for moving and adjusting a position of the irradiation optical system with respect to the test object in an optical axis direction, and the irradiation optical system. Detecting means for detecting the position of the system in the optical axis direction. Therefore, the versatility with respect to the change of the type of the test lens can be improved.

The invention according to claim 14 is the invention according to claims 11 and 1
14. The birefringence measurement apparatus according to 2 or 13, wherein the phase shifter, the analyzer, the light receiving element array, the phase shifter reciprocation switching means, the rotation means, the rotation angle detection means, and the imaging optical system are integrally mounted. A base moving means for moving the base in a direction substantially perpendicular to the optical axis of the optical system; and a base position detecting means for detecting a position of the base moved by the base moving means in a direction perpendicular to the optical axis of the optical system. . Therefore, when the test object is a lens with a short focal length,
The measuring method according to claim 3 can be realized.

[0037] The fifteenth aspect of the present invention provides the eleventh aspect and the first aspect.
14. The birefringence measuring apparatus according to 2 or 13, wherein the holding means for holding the test object is moved in a direction substantially perpendicular to an optical axis of an optical system, and the holding means is moved by the holding means moving means. Holding means for detecting a position in a direction perpendicular to the optical axis of the optical system. Therefore, when the test object is a parallel plate or a lens having a long focal length, the measuring method according to claim 3 can be realized. In the measurement of a lens having a long focal length, the size of the apparatus can be reduced.

According to a sixteenth aspect of the present invention, in the birefringence measuring apparatus according to the fourteenth or fifteenth aspect, a light receiving base is provided, on which the imaging optical system and the light receiving element array are integrally mounted. Therefore, the measuring method according to claim 4 can be realized.

According to the seventeenth aspect, the present invention provides the eleventh aspect and the first aspect.
16. The birefringence measuring apparatus according to 2, 13, 14 or 15, wherein an imaging magnification of the imaging optical system is variable. Therefore, even when the change in the birefringence of the test object is large in the test area, the measurement range can be expanded.

The invention according to claim 18 is the invention according to claims 9 and 1.
16. The birefringence measurement apparatus according to 1, 12, 13, 14, or 15, wherein the test object is a lens group including a plurality of lenses, and a holding unit that holds the lens group is provided. Therefore, even if the test object is a lens group including a plurality of lenses such as a writing optical system, the birefringence can be measured.

[0041]

FIG. 1 shows a first embodiment of the present invention.
A description will be given based on FIG. FIG. 1 shows an example of the configuration of a birefringence measuring apparatus used in the present embodiment.
Is held by a holder (not shown) as holding means. A linearly polarized light beam from a semiconductor laser 2 as a light source is circularly polarized by a λ / 4 plate 3 with respect to such a test object 1 and then acts as a microscope objective lens. The light is converted into divergent light by 4 and irradiates the test object 1. Here, an irradiation optical system 5 is configured to always make the light beam transmitted through the test object 1 by the lens 4 parallel to the optical axis. The lens 4 is mounted on a base 6 and can be advanced and retracted in the traveling direction of the light beam by rotating a stepping motor (not shown) for the purpose of adjusting the distance between the lens 4 and the test object 1. Here, moving means for the irradiation optical system 5 is configured, and a rotation origin position sensor (not shown) is attached to the stepping motor, and the lens 4 is moved by counting the number of pulses of the stepping motor. It is possible to detect the position (actually, the position of the lens 4 is detected based on the counting operation of the number of pulses in a personal computer, which will be described later ... detection means).
The distance between the lens 4 and the test object 1 is set so that the focal point of the lens 4 and the focus of the test object (test lens) 4 substantially coincide with each other. The light flux becomes almost parallel to the system optical axis.

The luminous flux transmitted through the test object 1 and converted into elliptically polarized light by the birefringence of the test object 1 is passed through the analyzer 7 and the lens 8 to the CCD camera 9 constituting a light receiving element array as light receiving means. To receive light. For the analyzer 7, a stepping motor 10 and a gear system 11 for rotating the analyzer 7 substantially around the traveling direction of light are provided as rotating means 12. A rotation origin position sensor (not shown) is attached to the stepping motor 10, and the rotation angle of the analyzer 7 can be detected by counting the number of pulses of the stepping motor 10 (actually, the rotation angle of the analyzer 7 can be detected). The rotation angle of the analyzer 7 is detected based on the counting operation of the number of pulses in a personal computer, which will be described later. A motor driver 13 drives the stepping motor 10 and drives the stepping motor 10 by receiving pulses from the personal computer 14 and the pulse generator 15.

The position of the lens 8 is adjusted so that an image-forming relationship is substantially established between the vicinity of the surface of the test object 1 and the CCD camera 9, and the internal birefringence of the material is sufficiently removed. Things are used. Here, an image forming optical system 16 for forming a light beam transmitted through the test object 1 by the lens 8 on the light receiving surface of the CCD camera 9 is formed. 1
Reference numeral 7 denotes a λ / 4 plate as a phase shifter for shifting the polarization state of the transmitted light of the test object 1, and is mounted on the base 18. The base 18 advances and retreats in a direction substantially perpendicular to the optical axis of the optical system by a phase shifter advancing / retracting switching means such as a cylinder (not shown), so that the irradiation light reaches the CCD camera 9 after passing through the test object 1. It can be freely inserted into and removed from the optical path up to. Accordingly, it is possible to generate both a state in which a phase difference of λ / 4 is applied and a state in which the polarization is not applied to the polarized light transmitted through the test object 1.

Further, the image captured by the CCD camera 9 is
The three-dimensional image data is transmitted to the personal computer 1 through the image input device 19.
The birefringence phase difference and principal axis direction of the test object 1 are calculated by a predetermined calculation method based on the image data and the rotation angle data of the stepping motor 10. An arithmetic processing function such as a CPU included in the personal computer 14 executes a function as an arithmetic means for calculating the birefringence of the lens 1 to be measured. By the way, CCD
The image captured by the camera 9 is displayed on a monitor of the personal computer 14 or a dedicated monitor.

Further, a light receiving base 20 on which the lens 8 and the CCD camera 9 are integrally mounted is provided. The light receiving base 20 is movable in the optical axis direction of the optical system for the purpose of maintaining the positional relationship between the lens 8 and the CCD camera 9 by the rotation of a stepping motor (not shown). Further, a common base 21 integrally provided with the analyzer 7, the lens 8, the CCD camera 9, the stepping motor 10, the λ / 4 plate 17, the base 18, and the light receiving base 20 is provided. The base 21 is movable by a guide 22 in a direction substantially perpendicular to the optical axis of the measuring optical system (up and down directions indicated by arrows in the drawing). In addition, this base 21 has the purpose of performing spatial division measurement,
Due to the rotation of the stepping motor 23, it moves back and forth in a direction substantially perpendicular to the optical axis of the optical system. Here, a base moving means 24 for moving and adjusting the base 21 in a direction orthogonal to the optical axis by the guide 22 and the stepping motor 23 is configured. For this base moving means 24, its base 21
Base position detecting means (not shown) for detecting the moving position of the camera
Is added.

The birefringence measuring method of the present embodiment using such a birefringence measuring device will be described. First, the test object 1 is set at a predetermined position by the holder,
In a state in which the λ / 4 plate 17 is not interposed in the optical path from the test object 1 to the CCD camera 9, that is, in a state in which no phase difference of λ / 4 is given to the polarized light transmitted through the test object. I do. In this state, the transmission axis direction of the analyzer 7 is rotated by (180 / n) degrees from the rotation origin. n is the number of measurement points set in advance. Each time the analyzer 7 rotates by (180 / n) degrees, the CCD image is fetched into the memory of the personal computer 14 to acquire the rotation angle data of the analyzer 7 and n CCD image data.

Next, the base 18 is advanced, and the λ / 4 plate 17 is interposed in the optical path from the test object 1 to the CCD camera 9, so that the transmitted polarization of the test object 1 has a phase difference of approximately λ / 4. give. In this case, the λ / 4 plate 17 and the base 18 are moved so that the light beam transmitted through the test object 1 and parallel to the optical axis of the optical system enters the surface of the λ / 4 plate 17 almost perpendicularly. Adjust the position. With the base 18 advanced, the transmission axis azimuth of the analyzer 7 is changed from the rotation origin by (18) as in the case described above.
While rotating by 0 / n) degrees, the CCD image data is taken into the memory of the personal computer 14 to obtain the rotation angle data of the analyzer 7 and n image data.

The birefringence of the test object 1 is obtained by the following arithmetic processing based on the total 2 × n image data obtained by the above procedure and the data of the rotation angle of the analyzer 7.

First, when the transmission axis direction of the analyzer 7 is rotated while the base 18 is retracted, the light intensity I ₀ detected by each pixel of the CCD camera 9 is expressed by the following equation (1): I ₀ = (1 / 2) (1−sin δsin2φcos2θ + cosδsin2θ) (1) Further, when the transmission axis direction of the analyzer 7 is rotated while the base 18 is advanced, the light intensity I ₄₅ detected by each pixel of the CCD camera 9 is expressed by the following equation (2). I ₄₅ = (1/2) (1 + cosδcos2θ−sinδcos2φsin2θ) (2) In these equations (1) and (2), θ is the transmission axis direction of the analyzer 7, δ is the birefringence phase difference of the test object 1, and φ is the main axis direction of the test object 1.

Here, assuming that the phases of the light intensity changes accompanying the rotation of the analyzer 7 are ψ ₀ and ψ ₄₅ , respectively, from the equations (1) and (2),
These phases ψ ₀ and ψ ₄₅ are as follows: ＝ ₀ = tan ⁻¹ (−tan 2φ)…… ＝ ＝ ₄₅ = tan ^-1 (-1 / tan δ cos 2φ) ……………… (4)

Further, based on the captured CCD image data and the rotation angle data of the analyzer 7, ψ ₀ and ψ ₄₅ are obtained by the following equations (5) and (6): ψ ₀ = tan ^-1 ｛Σ (I _0i · is calculated by _{sin2θ i) / Σ (I 0i} · cos2θ i)} ... (5) ψ 45 = tan -1 {Σ (I 45i · sin2θ i) / Σ (I 45i · cos2θ i)} ... (6) .

[0052] Therefore, from these (3) to ^{(6), δ = tan -1 (cosφ /} tanψ 45) ..................... (7) φ = (1/2) tan -1 (1 / tan ₀₎ ..................... (8), the phase difference [delta], the principal axis direction φ is obtained.

By the way, in the measuring optical system as shown in FIG. 1, the light irradiated to the test object 1 is almost collimated by the test object 1, so that the light transmitted through the test object 1 It becomes a parallel light flux having substantially the same area as the test object 1 in a plane perpendicular to the system optical axis. Here, in the case where the test object 1 is a lens used for a writing optical system, its area is usually large, so that the transmitted light flux also becomes large accordingly. Considering that the transmitted light flux of the test object 1 passes through the λ / 4 plate 17, λ / 4
The upper limit of the area of the plate 17 is about 30 mm in diameter, and it is costly to make a size larger than that,
The entire luminous flux transmitted through the test object cannot be transmitted through the λ / 4 plate 17. However, even if the transmitted light flux of the test object 1 is optically reduced according to the area of the λ / 4 plate 17,
In the case of a lens used in a writing optical system, the spatial resolution of measurement in the sub-scanning direction is reduced because the length in the sub-scanning direction is significantly shorter than the length in the main scanning direction.

For this reason, in this embodiment, as a space division measuring method corresponding to the third aspect of the present invention, the optical system elements after the λ / 4 plate 17 are integrated into the base 21 as a unit, and Is moved in a direction substantially perpendicular to the optical axis of the optical system, and the spatial image of the photoelastic interference fringe having substantially the same size as the test object 1 is partially divided and observed with the CCD camera 9, The measurement is performed. For example, as shown in FIG. 2, first, the base 21 is moved by the stepping motor 23 so that the measurement target area E1 of the test object 1 can be observed, and in this state, the phase difference and the principal axis direction are measured as described above. . Subsequently, the base 21 is moved by the stepping motor 23 so that the measurement target area E2 of the test object 1 can be observed. In this state, the phase difference and the principal axis direction are measured in the same manner. The base 21 is moved by the stepping motor 23 so that the region E3 can be observed, and the phase difference and the principal axis direction may be measured in this state. By joining the measurement results in the regions E1 to E3, the measurement results for the entire test object 1 are obtained. Even when the test object 1 is large in the height direction, the same divided measurement can be performed by preparing a stage movable in the height direction.

When the measurement target area of the test object 1 is determined, for example, an appropriate area can be determined by moving the base 21 and observing the photoelastic interference fringes captured and monitored by the CCD camera 9. You may make it select. Or,
A rotation origin position sensor is attached to the stepping motor 23, and the moving distance of the base 21 can be detected by the number of pulses supplied to the stepping motor 23. The measurement target area is determined in advance, and the base is moved to a position where the area can be observed. 21 may be automatically moved. In the latter case, the base 21 (accordingly, the λ / 4 plate 17
) Is detected (base position detecting means).

As described above, according to the basic configuration and operation of the present embodiment, it is possible to measure the birefringence of the entire test object 1 without lowering the resolution.

Next, a second embodiment of the present invention will be described with reference to FIGS. This embodiment corresponds to the fourth aspect of the present invention.

When performing the space division measurement as described with reference to FIG. 2, if the surface of the test object 1 has irregularities (depth),
When the light receiving base 20 is moved, the imaging relationship between the object surface and the light receiving surface of the CCD camera 9 is lost. For example, when the object 1 is a lens, an image forming relationship between the surface near the optical axis (near the vertex) of the lens set in the measuring device and the light receiving surface of the CCD camera 9 is established (focused). When the base 21 is moved in a direction perpendicular to the optical axis of the optical system to observe the end surface of the lens (test object 1), the lens has a curvature. The imaging relationship with the element surface does not hold.
Therefore, an optically blurred image is obtained, and when the measurement is performed using such an image, noise is included in the measurement result.

Therefore, in the present embodiment, the shape information of the test object 1 (roughness information of the test object surface) is stored in the measuring device in advance, and the shape information of the base 21 in the direction perpendicular to the optical axis of the optical system is stored. The measurement is performed while moving the light receiving base 20 in the optical axis direction of the optical system according to the amount of movement. Since the distance between the lens 8 and the CCD camera 9 is always constant and the light receiving base 20 is moved, the imaging magnification of the imaging optical system is always kept constant regardless of the movement of the light receiving base 20. For example, when the test object 1 is a convex lens, the surface of the end surface portion is located farther from the CCD camera 9 than the surface of the test object 1 near the optical axis. In this case, the radius of curvature of the lens to be inspected is R, the distance (lens height) from the optical system optical axis of the region to be observed by the imaging optical system is h, and the distance between the surface near the optical axis of the lens to be inspected and the observation region is Assuming that the depth difference from the surface is d, d is
(9) Equation d = R−√ (R ² −h ² )... (9)

Accordingly, when the base 21 is moved by h from the optical axis of the optical system from the state where the optical axis of the test object 1 is measured, the light receiving base 20 is advanced by d in the optical axis direction of the optical system. Is carried out, the test object 1 in the area to be measured
A clear image with a focused surface can be obtained, and accurate measurement can be performed.

A third embodiment of the present invention will be described with reference to FIGS. In the above description, the test object 1 is a lens that is axisymmetric and has a short focal length. However, the present embodiment relates to a case where the test object 1 is a non-axisymmetric lens.

As a lens used in the writing optical system, a non-axially symmetric lens whose focal length differs in two orthogonal directions (main scanning direction and sub scanning direction) is sometimes used. When measuring the birefringence of such a lens, irradiating the test object 1 with a spherical wave cannot make the transmitted light flux of the test object parallel to the optical axis of the optical system. As a result, the light beam transmitted through the test object 1 is obliquely incident on the surface of the λ / 4 plate 17, and the polarization of the light transmitted through the λ / 4 plate 17 is given an accurate phase difference of λ / 4. And a measurement error occurs. In addition, since the imaging manner of the test object 1 in the main scanning direction and the sub-scanning direction is different, a distorted image is obtained on the light receiving surface of the CCD camera 9 and accurate over the entire surface of the test object 1. Measurement becomes difficult.

Therefore, in the present embodiment, when such a non-axisymmetric lens is measured as the test object 1, the test object 1 is not irradiated with an axially symmetric light beam, and is, for example, a cylinder lens. A lens having a curvature only in one direction is placed between the lens 4 in FIG. 1 and a non-axisymmetric lens (test object 1), and a non-axisymmetric light beam is applied to the test object 1. , The transmitted light flux of the test object 1 is made parallel.

For example, as shown in FIG. 3, the focal length of the non-axisymmetric lens (test object 1) in the main scanning direction is f ₁ , and the focal length in the sub scanning direction is f ₂ (where f ₁ > f _2). ), Lens 4
The focal length f _o, installed cylinder lens between the lens 4 in FIG. 1 and the non-axisymmetric lens (specimen 1) 25
The focal length in the sub-scanning direction is f _c (the main scanning direction is plane, so the focal length is infinite), the thickness is t, and the refractive index is n _c
The distance between the lens 4 and the non-axisymmetric lens (test object 1) (distance between principal points) is Δ ₁ , and the distance between the cylinder lens 25 and the non-axisymmetric lens (test object 1) is Δ ₂ . _{when, Δ 1 = f 0 + f} 1 -t {1- (1 / n c)} ........................ (10) f 1 -t {1- (1 / n c)} = {f c (Δ ₂ −f ₂ ) / (Δ ₂ −f ₂ −f ₂ }) + Δ ₂ ... When the intervals Δ ₁ and Δ ₂ are set so as to satisfy (11), a non-axisymmetric lens is obtained. Light transmitted through the (test object 1) can be made substantially parallel. This enables measurement by the method of the above-described embodiment. Further, if each lens is mounted on a driving means such as a stage and the shape data is stored in the measuring device, it is possible to automatically set the arrangement of the optical system.

FIGS. 1 and 2 show a fourth embodiment of the present invention.
This will be described with reference to FIG. The present embodiment is an example applied to a case where the test object 1 is a parallel plate or a lens having a long focal length.

When the test object 1 is a parallel flat plate, even if the test object 1 is irradiated with a spherical wave, the light beam transmitted through the test object 1 is not parallelized. Irradiate. Specifically, an axially symmetric lens is provided on the optical axis between the lens 4 and the test object 1 in FIG. 1, and the focal point of the axially symmetric lens and the focal point of the lens 4 are matched. Thus, the test object can be irradiated with the parallel light beam, and the measurement can be performed by the method of the above-described embodiment. In this case, an axially symmetric lens disposed between the lens 4 and the test object 1 is mounted on a stage that can move back and forth in the optical axis direction of the optical system, and the shape data of the test object 1 can be stored in the measuring device. For example, automatic setting of the optical system arrangement is possible.

When the test object 1 is a lens having a long focal length, the distance between the lens 4 and the test object 1 must be adjusted so that the focus of the lens 4 in FIG. It is necessary to increase the size, and the measuring device becomes large. for that reason,
In the present embodiment, when the test object 1 is a lens having a long focal length, the test object is measured by irradiating the test object 1 with a parallel light beam in the same manner as in the parallel plate measurement, by imitating the lens as a parallel plate. Is carried out. Actually, since the transmitted light beams are not parallel plates, the transmitted light beams are not strictly parallelized, which causes a measurement error. However, in the case of a lens having a long focal length, the error is very small and can be ignored. This can prevent the measurement device from being enlarged.

The space division measurement when the test object 1 is a parallel plate or a lens having a long focal length will be described. When irradiating the test object 1 with a parallel light beam, the test object 1
If the light beam having a diameter sufficient to cover the entire surface of the optical system is not irradiated, the space division measurement while the base 21 in FIG. 1 is moved in a direction substantially perpendicular to the optical axis of the optical system as described above cannot be performed. When the area of the test object 1 is large, an expensive optical system is required to create a light beam that can cover the entire surface of the test object 1.

In order to solve this problem, in this embodiment corresponding to the fifteenth aspect, the test object 1 and its holder (holding means) can be moved in a direction perpendicular to the optical axis of the optical system. Mounted on a stage (holding means moving means), the stage is moved in a direction substantially perpendicular to the optical axis of the optical system, and the space division measurement is performed while detecting the position by the holding means position detecting means. At this time, the light receiving base 20 does not need to be moved because the base 21 side is fixed and the surface of the test object 1 can be regarded as a flat surface.

When the test object 1 is an aspherical lens, the light beam transmitted through the test lens cannot be strictly collimated by any of the above-mentioned apparatuses and methods. The above method may be applied by imitating a spherical lens or a parallel plate.

FIGS. 1 and 4 show a fifth embodiment of the present invention.
This will be described with reference to FIG. This embodiment corresponds to the invention described in claim 5.

The output range of the measurement result of the birefringence phase difference by the measurement method of the first embodiment is -λ / 4 to + λ.
/ 4 (λ: wavelength of the semiconductor laser 2 used for measurement) is limited to a range, and a large birefringence phase difference measurement result exceeding the range includes uncertainty due to the light source wavelength. That is, assuming that the true value of the birefringence phase difference is Δ and the measured value is δ, both have the following relationship: Δ = δ ± n · λ (n: an integer) (12) That is, the value of the integer n cannot be specified.

Therefore, in the present embodiment, with respect to the result of measuring the phase difference between the adjacent pixels (adjacent light receiving elements) of the CCD camera 9, the difference is detected, and the difference is corrected, thereby limiting the light source wavelength. It is intended to obtain a wide measurement range that is not affected.

First, FIG. 4A shows an example of the cross-sectional distribution of the phase difference measurement result, but the measurement result is limited to the range of -λ / 4 to + λ / 4. The horizontal axis in FIG. 4A represents the position of the CCD camera 9. Here, when the difference between the measured values is taken between adjacent pixels in the CCD camera 9, a step near λ / 2 is detected at a position beyond the measurement range. Therefore, by adding or subtracting λ / 2 to the measured value so as to correct the step at that position, the cross-sectional distribution of FIG. 4A can be converted as shown in FIG. Measurement results can be obtained in a wide range that is not affected by the measurement.

A sixth embodiment of the present invention will be described with reference to FIG. This embodiment corresponds to the invention described in claim 17.

In the present embodiment, for example, the imaging optical system 16 in the measuring apparatus shown in FIG. 1 is constituted by a plurality of lenses, and the distance between the lenses is changed to change the combined focal length, whereby the imaging optical system is changed. The magnification of the system 16 becomes variable. When the fringe interval of the photoelastic interference fringe is narrow and the fringe interval is smaller than the size of a single pixel of the CCD camera 9, if the magnification of the imaging optical system 16 is increased, the interference fringe on the light receiving surface of the CCD camera 9 is increased. The interval widens. Thereby, interference fringes can be detected, and the comparison processing of the measured values between the adjacent pixels of the CCD camera 9 by the method of the fifth embodiment described above can be performed, so that the measurement range can be expanded.

The seventh embodiment of the present invention will be described with reference to FIGS.
This will be described with reference to FIG. This embodiment corresponds to the invention described in claim 6.

According to the method of the fifth embodiment described above, an infinite measurement range can be obtained. However, processing for comparing or correcting all the adjacent pixels of the CCD camera 9 in the test area is required. It takes time.

Therefore, in the present embodiment, the measurement range of the birefringence phase difference by the measurement method of the first embodiment, −λ /
An object of the present invention is to provide a method for performing a process of expanding 4 to + λ / 4 from −λ / 2 to + λ / 2 in a short time.

In FIG. 1, the light beam transmitted through the test object 1 is a CCD.
When the λ / 4 plate 17 is interposed in the optical path up to the camera 9, the major axis direction of the elliptically polarized light transmitted through the λ / 4 plate 17 is used as information. For example, in FIG. 5, if α is the major axis direction of the elliptically polarized light transmitted through the λ / 4 plate 17, when α is in the first and second quadrants, the phase difference measurement value is not processed, and In the case of the quadrant, a process of subtracting λ / 2 from the measured value, and in the case of the fourth quadrant, adding λ / 2 to the measured value. Thereby, the measurement range −λ / 4 to + λ / 4
Can be expanded from −λ / 2 to + λ / 2, and the processing can be performed in a short time. Further, in the method of the fifth embodiment described above, an attempt is made to detect a difference of λ / 2 between measured values between adjacent pixels. However, when there is noise on the measured values, measurement between adjacent pixels is performed. In some cases, the difference between the values does not become close to λ / 2, in which case a processing error occurs. In the present embodiment, since the comparison processing of the measured values between the adjacent pixels is not performed, the difference detection error and the correction error can be completely eliminated.

The eighth embodiment of the present invention will be described with reference to FIGS.
This will be described with reference to FIG. This embodiment corresponds to the invention described in claim 7, and is a combination of the fifth embodiment and the seventh embodiment.

First, according to the method of the seventh embodiment, -λ /
The measurement range of 4 to + λ / 4 is expanded to −λ / 2 to + λ / 2, and then the measurement range is expanded to infinity by the method of the fifth embodiment. The measurement range can be expanded in the first stage without any processing errors, and in the second stage, the amount of steps detected between adjacent pixels is expanded from λ / 2 to λ, making it easier to detect steps. Therefore, the detection error can be reduced. Therefore, even a large birefringence exceeding the wavelength of the light source used in the apparatus can be measured with higher accuracy.

The ninth embodiment of the present invention will be described with reference to FIGS.
This will be described with reference to FIG. This embodiment corresponds to the eighth aspect of the present invention. In the present embodiment, a configuration for estimating the absolute amount of the birefringence phase difference at a position set as a reference in the two-dimensional test space is added. In FIG. 6, 3
1 is a white light source unit, 32 is a polarizing plate 33 and a λ / 4 plate 3
4 is a circular polarizer, 35 is a polarizing plate 36 and a λ / 4 plate 37
And a circular polarizer. As a result, the test object 1 is irradiated with circularly polarized light, and when there is no birefringence of the test object 1, the respective polarizing plates 33 and 36 are arranged such that an extinction state is obtained when viewed from the direction of the observer in the figure. Has been adjusted.

Here, due to the interference by the circularly polarized light, the photoelastic interference fringes observed from the direction of the observer in the figure are affected only by the phase difference of the test object 1, and the light source is a white light source unit. Since 31 is used, the interference fringes are observed by coloring. Since the λ / 4 plates 34 and 37 have wavelength dependence,
Although some errors occur as the wavelength deviates from the center wavelength,
Since there is a certain relationship between the interference color and the phase difference (such as Newton's color scale), it is possible to roughly estimate the phase difference at the reference position in the two-dimensional test space by looking at the interference fringes. .

Then, assuming that the phase difference measurement result obtained by the above-described measuring method is δ, the absolute amount Δ is
If the integer n can be specified by the above equation (12), the absolute amount Δ of the phase difference can be obtained.

Since the approximate range in which the phase difference should be obtained can be estimated by observing the interference fringes with the configuration shown in FIG. 5, the integer n in the equation (12) can be determined so as to fall within the range.

Accordingly, as a procedure, first, the two-dimensional spatial distribution of the birefringence phase difference of the test object 1 is measured by the birefringence measuring device as shown in FIG. 1, and then the configuration as shown in FIG. The absolute value of the birefringence phase difference at the reference position in the arbitrarily set two-dimensional test space is estimated, that is, the integer n at the reference position is determined. Next, the absolute amount of the birefringence phase difference in the entire two-dimensional space can be known by applying the integer n to all the measured values of the two-dimensional space distribution measured earlier.

As a method of knowing (estimating) the absolute amount of the birefringence phase difference at the reference position in the two-dimensional object space, in addition to the discrimination method based on interference colors, for example, a rotation analyzer method In the point measurement method described above, measurement may be performed using multiple wavelengths as a light source.

A tenth embodiment of the present invention will be described. This embodiment corresponds to the invention described in claim 18.

This embodiment is applied to a case where the test object 1 is a lens for a writing optical system in a laser printer or the like. In such a case, the test object 1 is constituted by a lens group including a plurality of lenses. Here, since the synergistic effect of the birefringence of each lens affects the beam transmitted through the lens group in the actual use state of the writing optical system, the measured value of the birefringence in the actual use state of the lens group indicates the transmitted beam. This is useful information for evaluation. Therefore, in the present embodiment, each of such lens groups is laid out on the base in the same manner as in the actual use state, and then the base is set on the birefringence measuring apparatus shown in FIG. The lens 4 for irradiating the object 1 (lens group) with divergent light and the object 1
Is set so as to correspond to the distance between the point light source and the lens group during actual use in the writing optical system. This makes it possible to measure and evaluate the birefringence of the lens group in a more practical use state.

[0091]

According to the first, second, and ninth aspects of the present invention, it becomes possible to perform birefringence measurement that is hardly affected by noise such as dirt on the surface of the test object.

According to the third aspect of the present invention, accurate measurement can be performed over the entire surface of the test object even when the area of the test object is large.

According to the fourth aspect of the invention, accurate measurement can be performed over the entire surface of the test object.

According to the fifth aspect of the present invention, a wide (infinite) wide measurement range not limited by the light source wavelength can be obtained.

According to the sixth aspect of the present invention, the measuring range in the birefringence measuring method of the first aspect is from -λ / 4 to + λ.
The process of expanding / 4 from −λ / 2 to + λ / 2 can be performed accurately in a short time.

According to the seventh aspect of the present invention, a wide (infinite) wide measurement range which is not limited by the wavelength of the light source can be obtained more accurately.

According to the eighth aspect of the present invention, it is possible to determine the absolute value of the birefringence phase difference in the entire two-dimensional test area.

According to the tenth aspect, birefringence measurement can be performed in a short time and with high spatial resolution.

According to the eleventh aspect, even when the test object has a curvature like a lens, simple, short time, high spatial resolution, and high precision measurement can be performed.

According to the invention of claims 12 and 13,
The versatility for changing the type of the lens to be inspected can be improved.

According to the fourteenth aspect, the measuring method according to the third aspect can be realized when the test object is a lens having a short focal length.

According to the fifteenth aspect, the measuring method according to the third aspect can be realized when the test object is a parallel plate or a lens having a long focal length. In the measurement of a lens having a long focal length, the size of the apparatus can be reduced.

According to the invention of claim 16, claim 4
The described measuring method can be realized.

According to the seventeenth aspect, even when the birefringence of the test object greatly changes in the test area, the measurement range can be expanded.

According to the eighteenth aspect of the present invention, even if the test object is a lens group composed of a plurality of lenses, such as a writing optical system, the birefringence can be measured.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a birefringence measurement device used in each embodiment of the present invention.

FIG. 2 is a front view showing how a measurement target area is divided.

FIGS. 3A and 3B are diagrams for explaining the operation of the correction optical system, where FIG. 3A is a plan view as viewed in a main scanning direction, and FIG. 3B is a side view as viewed in a sub-scanning direction.

FIG. 4 is a characteristic diagram showing a cross-sectional distribution before and after correction of a phase difference measurement result.

FIG. 5 is an explanatory diagram for explaining a major axis direction of elliptically polarized light.

FIG. 6 is a side view of an optical system showing a configuration for estimating an absolute amount of a birefringence phase difference.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 object 2 light source 5 irradiation optical system 7 analyzer 9 light receiving element array, light receiving means 12 rotating means 16 imaging optical system 17 phase shifter 20 light receiving base 21 base 24 base moving means

Claims (18)

[Claims] An object is obtained by irradiating a test object with substantially circularly polarized light, receiving a light beam transmitted through the test object by light receiving means only through an analyzer, and rotating the analyzer. The polarization information of the test object transmitted light obtained from the light intensity change, and the light flux transmitted through the test object was received by the light receiving means via a phase shifter and the analyzer, and the analyzer was rotated. A birefringence measurement method wherein the birefringence of the test object is obtained based on the polarization information of the transmitted light of the test object obtained from the change in light intensity obtained at the time and the polarization information. 2. A state in which the phase shifter is interposed and a state in which the phase shifter is not interposed in an optical path from the test object to the light receiving unit by moving the phase shifter in a direction other than the optical axis of the optical system. 2. The method for measuring birefringence according to claim 1, wherein said method is used to generate a birefringence. 3. The apparatus according to claim 1, wherein the test area of the test object is divided into a plurality of areas in a plane perpendicular to the optical axis of the optical system, and measurement data relating to polarization information is acquired. Birefringence measurement method. 4. A plurality of areas within a plane perpendicular to an optical axis of an optical system, while maintaining an imaging relationship between the surface of the object and the light receiving surface of the light receiving means at all times. Divided into
3. The method for measuring birefringence according to claim 1, wherein measurement data relating to polarization information is obtained. 5. A light-receiving element array comprising a plurality of light-receiving elements, wherein the light-receiving means detects a difference between birefringence phase differences measured between adjacent light-receiving elements, and the difference is close to a predetermined amount. 3. The birefringence measurement method according to claim 1, wherein the difference is corrected to extend the measurement range of the calculated birefringence phase difference. 6. The method according to claim 1, wherein a major axis direction of the elliptically polarized light transmitted through the phase shifter is detected, and a measurement range of the calculated birefringence phase difference is expanded based on the information of the major axis direction.
Or the birefringence measurement method according to 2. 7. The light receiving means is a light receiving element array comprising a plurality of light receiving elements, detects a major axis direction of the elliptically polarized light transmitted through the phase shifter, and calculates a multiplicity calculated based on the information of the major axis direction. After enlarging the measurement range of the refractive phase difference, between the adjacent light receiving elements of the light receiving element array, a difference between the measured birefringence phase differences is detected, and when the difference is close to a predetermined amount, the difference is corrected. 3. The method for measuring birefringence according to claim 1, wherein the measurement range of the calculated birefringence phase difference is expanded. 8. An absolute amount of a birefringence phase difference at a reference position within an arbitrarily set test area, and the estimated absolute amount of a birefringence phase difference is measured in two dimensions. 3. The birefringence measurement method according to claim 1, wherein the absolute value of the birefringence phase difference in the entire test area is measured by applying the measurement to all the measured values of the spatial distribution. 9. A light source for irradiating the test object with substantially circularly polarized light, a phase shifter for changing a polarization state of transmitted light transmitted through the test object, and light transmitted through the phase shifter. An analyzer for detecting the polarization state of the light; a light receiving means for receiving light transmitted through the analyzer; and a state in which the phase shifter is interposed on an optical path from the test object to the light receiving means. Phase shifter advancing / retracting switching means for generating a state not to be rotated; rotating means for rotating the analyzer around its optical axis; rotation angle detecting means for detecting a rotation angle of the analyzer by the rotating means; Holding means for holding an inspection object; and calculation means for calculating birefringence of the test object based on a light reception output detected by the light reception means and a rotation angle detected by the rotation angle detection means. Birefringence measurement device. 10. The birefringence measuring apparatus according to claim 9, wherein said light receiving means comprises a light receiving element array in which a plurality of light receiving elements are juxtaposed. 11. An irradiation optical system for always making a light flux of transmitted light transmitted through the test object substantially parallel to an optical axis, and a light receiving surface of the light receiving element array for transmitting light transmitted through the test object. 11. An imaging optical system for forming an image thereon.
The birefringence measuring device according to the above. 12. The birefringence measuring apparatus according to claim 11, wherein the irradiation optical system comprises a plurality of optical systems that can be freely combined. 13. A moving means for moving and adjusting a position of the irradiation optical system in the optical axis direction with respect to the test object, and a detecting means for detecting a position of the irradiation optical system in the optical axis direction. Or the birefringence measurement device according to 12. 14. A base on which the phase shifter, the analyzer, the light receiving element array, the phase shifter retreat switching means, the rotation means, the rotation angle detection means and the imaging optical system are integrally mounted, and the base is an optical system. 13. A base moving means for moving the base in a direction substantially perpendicular to the optical axis, and base position detecting means for detecting a position of the base moved by the base moving means in a direction perpendicular to the optical axis of the optical system. 14. The birefringence measurement device according to 13. 15. A holding means moving means for moving the holding means for holding the test object in a direction substantially perpendicular to an optical system optical axis; and an optical system optical axis of the holding means moving from the holding means moving means. 14. The birefringence measurement device according to claim 11, further comprising: a holding unit that detects a position in a vertical direction. 16. A light-receiving base on which the imaging optical system and the light-receiving element array are mounted integrally.
Or the birefringence measurement device according to 15. 17. The birefringence measuring apparatus according to claim 11, wherein the imaging magnification of the imaging optical system is variable. 18. The birefringence measurement apparatus according to claim 9, wherein the test object is a lens group including a plurality of lenses, and a holding unit that holds the lens group is provided.