Optical measurement device, method of manufacturing optical measurement device, and optical measurement method

Abstract

To provide an optical measurement device capable of performing lens surface interval measurement and decentering amount measurement highly accurately and efficiently.SOLUTION: There is provided an optical measurement device for measuring a lens surface interval and a lens decentering amount of a detection object optical system having a plurality of optical surfaces. An image-forming optical system has an objective lens, an image-forming lens, and a light intensity detection surface. A rear focal point of the objective lens coincides with a front focal point of the image-forming lens, and a rear focal point of the image-forming lens coincides with the light intensity detection surface.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an optical measurement device, a method for manufacturing the optical measurement device, and an optical measurement method.

Background Art

[0002] Conventionally, when measuring the surface interval of a lens in a non-contact and non-destructive manner, in a test optical system having a large total thickness of a glass material having a plurality of optical surfaces, regardless of the thickness of the glass material, a surface interval measurement device capable of measuring the surface interval of the lens of the test optical system with high accuracy is known (see, for example, Patent Document 1).

[0003] In such a surface interval measurement device disclosed in Patent Document 1, light from a light source with a short coherence distance is divided into a first light beam and a second light beam, and the second light beam is focused on the test surface. Then, when the reflection mirror in the first optical path is swept in the optical axis direction, according to the difference in OPL between the first light beam and the second light beam, a change in the brightness and darkness of the interference fringes occurs on the imaging surface, and the contrast of the interference fringes becomes maximum when the difference in DAL between the first light beam and the second light beam disappears. The position of the reflection mirror at this time is measured with a length measuring instrument, and the difference in the measured values between adjacent test surfaces is divided by the group refractive index of the medium, so that the surface interval of the lens of the test optical system can be measured with high accuracy.

[0004] On the other hand, in a test optical system having a plurality of optical surfaces, when the required optical performance cannot be obtained, it may be caused by the decentration of the lens surface. For this reason, a lens decentration measurement device for accurately measuring the decentration of each lens surface of the test optical system is known (see, for example, Patent Document 2).

[0005] In such a lens eccentricity measuring device disclosed in Patent Document 2, a projection index projected from a light projecting optical system is projected onto a surface to be inspected of a lens to be inspected, and a reflected image formed on this surface to be inspected is enlarged and observed by a light receiving optical system to measure the amount of tilt. By measuring such an amount of tilt from the first surface to the final surface of the lens to be inspected that constitutes the optical system to be inspected and calculating the eccentricity of each lens surface, it is said that even in an optical system to be inspected having a plurality of optical surfaces, the eccentricity of each lens that constitutes the optical system to be inspected can be measured.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, when performing both the measurement of the lens surface interval and the measurement of the lens eccentricity as described above with one measuring device, in a setting where the eccentricity measurement can be performed with high accuracy, the accuracy of the surface interval measurement decreases, etc., and it has been difficult to measure both the surface interval measurement and the eccentricity measurement with high accuracy.

[0008] The present invention has been made in view of the above problems, and an object thereof is to provide an optical measuring device capable of accurately and efficiently performing both the measurement of the lens surface interval and the measurement of the eccentricity.

Means for Solving the Problems

[0009] The optical measuring device of the present invention has the following configuration. (1) The optical measurement device according to the first aspect of the present invention is an optical measurement device for measuring the lens surface interval and lens eccentricity of an optical system under test having a plurality of optical surfaces, and includes a beam splitting element that splits light from a light source with a short coherence distance into a first light beam and a second light beam, an optical path length variable member that changes the optical path length of the first light beam according to the position of the optical surface to be measured, a condensing element that condenses the second light beam at a predetermined position regarding the optical surface to be measured among the optical system under test disposed in the optical path of the second light beam, a beam combining element that superimposes the first light beam with a changed optical path length and the second light beam reflected by the optical surface to be measured, a light intensity detection sensor that detects the light intensity distribution of the interference fringes generated by the first light beam and the second light beam with a light intensity detection surface, a surface interval calculation processor that calculates the surface interval of the optical system under test based on the change amount of the DAL of the first light beam and the contrast change of the light intensity distribution, and an imaging optical system that forms an image of an image generated by the reflection of the second light beam on the optical surface on the light intensity detection surface. The imaging optical system includes an objective lens, an imaging lens, and the light intensity detection surface, and is characterized in that the rear focal point of the objective lens coincides with the front focal point of the imaging lens, and the rear focal point of the imaging lens coincides with the light intensity detection surface. Here, DAL (Dispersion conforming Air Length) is defined by the following formula (1). DAL = Σ (material length × group refractive index) ··· (1) Here, Σ indicates the sum of the number of surfaces of the entire optical system through which the light emitted from the light source passes.

[0010] The manufacturing method of the optical measurement device of the present invention has the following configuration. (2) The manufacturing method of the optical measurement device according to the second aspect of the present invention is the manufacturing method of the optical measurement device described in the first aspect, and when manufacturing the imaging optical system, the condensing point of the second light beam is arranged at the focus of a mirror surface with a known curvature, and the position of the imaging lens is adjusted so that the number of interference fringes due to the interference between the first light beam and the second light beam becomes zero by illuminating the light intensity detection surface with parallel light, and the interval between the objective lens and the imaging lens is adjusted.

[0011] (3) The manufacturing method of the optical measurement device according to the third aspect of the present invention is the manufacturing method of the optical measurement device described in the first aspect, wherein when manufacturing the imaging optical system, when the distribution of the OPL in the second light beam on the light intensity detection surface coincides with the distribution of the OPL of the first light beam on the light intensity detection surface, the distribution of the DAL in the second light beam on the light intensity detection surface coincides with the distribution of the DAL of the first light beam on the light intensity detection surface. Here, OPL (Optical Path Length) is defined by the following formula (2). OPL = Σ (material length × refractive index) ··· (2) Here, the optical path length is used as a term when expressing without distinguishing between DAL and OPL.

[0012] The optical measurement method of the present invention has the following configuration. (4) The optical measurement method according to the fourth aspect of the present invention is an optical measurement method for measuring the lens surface interval and lens decentration amount of an optical system under test having a plurality of optical surfaces, including a light beam splitting step of splitting light from a light source with a short coherence distance into a first light beam and a second light beam, an optical path length variable step of changing the optical path length of the first light beam according to the position of the optical surface to be measured, a light condensing step of condensing the second light beam at a predetermined position related to the optical surface to be measured among the optical systems under test arranged in the optical path of the second light beam, a light beam combining step of superposing the first light beam with the changed optical path length and the second light beam reflected by the optical surface to be measured, a light intensity detection step of detecting the light intensity distribution of the interference fringes generated by the first light beam and the second light beam by a light intensity detection surface, and a surface interval calculation step of calculating the surface interval of the optical system under test based on the change amount of the DAL of the first light beam and the contrast change of the light intensity distribution. The imaging optical system having an objective lens, an imaging lens, and a light intensity detection surface forms an image of the image generated by the reflection of the second light beam on the optical surface on the light intensity detection surface, and the rear focal point of the objective lens coincides with the front focal point of the imaging lens, and the rear focal point of the imaging lens coincides with the light intensity detection surface.

[0013] Another optical measuring device of the present invention has the following configuration. (5) The optical measuring device according to the fifth aspect of the present invention is an optical measuring device for measuring the lens surface interval and the lens decentration amount of an optical system to be measured having a plurality of optical surfaces, and includes a beam splitting element that splits light from a light source with a short coherence distance into a first light beam and a second light beam, an optical path length variable member that changes the optical path length of the first light beam according to the position of the optical surface to be measured, a condensing element that condenses the second light beam at a predetermined position related to the optical surface to be measured among the optical systems to be measured disposed in the optical path of the second light beam, a beam combining element that superimposes the first light beam with a changed optical path length and the second light beam reflected by the optical surface to be measured, a light intensity detection sensor that detects the light intensity distribution of the interference fringes generated by the first light beam and the second light beam with a light intensity detection surface, a surface interval calculation processor that calculates the surface interval of the optical system to be measured based on the change amount of the DAL of the first light beam and the contrast change of the light intensity distribution, and an imaging optical system that forms an image of an image generated by reflection of the second light beam on the optical surface on the light intensity detection surface. The imaging optical system has an objective lens, an imaging lens, and the light intensity detection surface, the rear focal point of the objective lens coincides with the front focal point of the imaging lens, and the rear focal point of the imaging lens coincides with the light intensity detection surface. The imaging optical system is such that the number of interference fringes generated when the DAL distribution of the second light beam up to the light intensity detection surface coincides with the DAL distribution of the first light beam up to the light intensity detection surface is examined in advance, the condensing point of the second light beam is arranged at the focus of a mirror surface with a known curvature, the light intensity detection surface is illuminated with parallel light, and the interval between the objective lens and the imaging lens is adjusted so that the same number of interference fringes as the number examined in advance is observed due to the interference between the first light beam and the second light beam.

[0014] Another method for manufacturing an optical measuring device of the present invention has the following configuration. (6) The method for manufacturing an optical measurement device according to the sixth aspect of the present invention is the method for manufacturing an optical measurement device according to claim 5, wherein when manufacturing the imaging optical system, the distribution of the DAL from the second light beam to the light intensity detection surface is the same as the distribution of the DAL from the first light beam to the light intensity detection surface. A step of preliminarily examining the number of interference fringes generated when they match, a step of arranging the focal point of the second light beam at the focus of a mirror surface with a known curvature and illuminating the light intensity detection surface with parallel light, and the first light beam and the second light beam. And a step of adjusting the distance between the objective lens and the imaging lens so that the same number of interference fringes as the preliminarily examined number of interference fringes due to the interference of the two light beams is observed.

Effect of the Invention

[0015] According to the present invention, it becomes possible to provide an optical measurement device capable of highly accurately and efficiently measuring the surface interval and eccentricity of a lens.

Brief Description of the Drawings

[0016]

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[0017] Hereinafter, with reference to the drawings, an optical measurement device, a method for manufacturing the optical measurement device, and an optical measurement method according to an embodiment of the present invention will be described. Note that each of the embodiments described below is specifically described to better understand the gist of the invention, and unless otherwise specified, the present invention is not limited to a specific range. In addition, the drawings used in the following description may show, for the sake of clarity, the characteristic parts enlarged for convenience, and the dimensional ratios of the respective components are not necessarily the same as the actual ones. Also, the device configurations exemplified in the following description are merely examples, and the present invention is not necessarily limited thereto, and the device configuration can be appropriately changed within the range where the effects are not changed.

[0018] In the following description, parallel light includes light that is not inclined with respect to the optical axis and is completely parallel to the optical axis, and light that is inclined within a range of ±10° or less with respect to the optical axis. [Optical Measurement Device: First Embodiment] FIG. 1 is a schematic configuration diagram showing the optical measurement device according to the first embodiment of the present invention. The optical measurement device 100 includes a light source 101, a beam splitter (beam splitting element) 102, a beam splitter 103, a beam splitter (beam combining element) 104, collimator lenses 105 and 106, an objective lens (condensing element) 108, an imaging lens 109, a reflection mirror 111, a reference mirror (optical path length variable member) 112, an imaging camera (light intensity detection sensor) 114 having a photodetector (light intensity detection surface) 113, and a computer (surface interval detection processor) 115.

[0019] Among such optical measurement devices 100, a reflection detection system 120 is constituted by each member except the reference mirror (optical path length variable member) 112 and the computer (surface interval detection processor) 115. The entire reflection detection system 120 can be moved with respect to the optical system M to be inspected. Each member constituting these reflection detection systems 120 is integrated, and as a result, the positional relationship between the objective lens 108 and the imaging lens 109 is fixed.

[0020] Also, on the optical path of the objective lens 108, an optical system M to be inspected having a plurality of optical surfaces, which is the measurement object, is arranged. The optical system M to be inspected is, for example, a lens of a camera, a lens of a digital camera, a lens of an endoscope, or the like. These lenses have a lens group composed of a plurality of lenses.

[0021] Among these members constituting the optical measurement device 100, the objective lens 108, the imaging lens 109, and the photodetector 113 constitute an imaging optical system 117.

[0022] Also, the path from the light source 101 through the beam splitter 102, the collimator lens 106, the reflection mirror 111, the reference mirror 112, and the beam splitter 104 to the photodetector 113 constitutes the optical path of the reference light beam (first light beam) L1.

[0023] Also, the path from the light source 101, through the beam splitter 102, the collimator lens 105, the objective lens 108, the optical system under test M, the beam splitter 103, the imaging lens 109, and the beam splitter 104 to the photodetector 113 constitutes the optical path of the measurement light beam (second light beam) L2.

[0024] The light source 101 uses a light source with a wide spectral width and a short coherence length. As the light source 101, for example, a superluminescent diode (hereinafter referred to as SLD) can be used. Such an SLD emits light with a coherence length of, for example, 0.1 μm to 200 μm, or a full width at half maximum of the wavelength distribution of 1 nm to 500 nm. Also, the light source 101 is not limited to the SLD, and a semiconductor laser, a short pulse laser, a halogen lamp, a light emitting diode, or the like that can operate below the threshold current can also be used.

[0025] The beam splitter 102 is a beam splitting element that splits the light emitted from the light source 101 into a first light beam L1 that is a reference light beam and a second light beam L2 that is a measurement light beam.

[0026] The beam splitter 103 transmits the measurement light beam L2 toward the objective lens 108 and reflects the measurement light beam L2 reflected by the optical system under test M toward the imaging lens 109.

[0027] The beam splitter 104 transmits the measurement light beam L2 that has passed through the imaging lens 109 toward the photodetector 113, transmits the reference light beam L1 that has passed through the reflection mirror 111 toward the reference mirror 112, reflects the reference light beam L1 that has been reflected by this reference mirror 112 and incident on the beam splitter 104 again toward the photodetector 113, and is a beam combining element that combines the reference light beam L1 and the measurement light beam L2.

[0028] The collimator lens 105 converts the measurement light beam L2, which is one of the light beams split by the beam splitter 102, into parallel light and emits it. Further, the collimator lens 106 converts the reference light beam L1, which is the other light beam split by the beam splitter 102, into parallel light and emits it toward the reflection mirror 111 side. As these collimator lenses 105 and 106, for example, a microscope objective lens can be used.

[0029] The objective lens 108 (condensing element) condenses the measurement light beam L2 that has passed through the beam splitter 103 toward the optical system M to be inspected. Further, the imaging lens 109 forms an image of the measurement light beam L2 that has passed through the optical system M to be inspected toward the photodetector 113. The objective lens 108 and the imaging lens 109 that constitute the imaging optical system 117 are adjusted in their arrangement positions during the manufacture of the optical measurement device 100, as will be described later. Further, the reflection detection system 120 has the position on the optical axis of the measurement light beam L2 controlled via the computer 115 so that the focal point (condensing point) of the measurement light beam L2 can be aligned with an arbitrary position of the optical system M to be inspected.

[0030] The reflection mirror 111 is composed of a reflecting mirror that reflects the reference light beam L1 made parallel by the collimator lens 106 at a right angle toward the reference mirror 112. The reference mirror (optical path length variable member) 112 is formed so as to be movable along the optical axis direction of the reference light beam L1. The movement control of such a reference mirror 112 can be performed via an interface by a measurement control program installed in the computer 115. Further, a length measuring device 118 is connected to the reference mirror 112. The length measuring device 118 detects the position of the reference mirror 112 in the optical axis direction and outputs the position information to the computer 115. Such a reference mirror (optical path length variable member) 112 includes a function in which its position is measured by a length measuring instrument, and the amount of change in the optical path length can be obtained.

[0031] The imaging camera 114 includes a photodetector 113 disposed on the optical paths of the reference light beam L1 and the measurement light beam L2. The photodetector 113 can use a one-dimensional or two-dimensional solid-state imaging device such as a CCD. Further, the photodetector 113 may use a C-MOS sensor, an image dissector, a photodiode, a photomultiplier, a line sensor, etc.

[0032] For example, if a two-dimensional photoelectric conversion element is used as the photodetector 113, the reflection images from each surface of the lens to be measured of the optical system M to be inspected can be confirmed on the monitor 119 connected to the computer 115. Thereby, the positioning of the imaging optical system 117 and the optical system M to be inspected can be facilitated.

[0033] The photodetector 113 of such an imaging camera 114 detects the light intensity distribution of the interference fringes generated by the reference light beam L1 and the measurement light beam L2. Interference fringes are generated if the difference in OPL between the reference light beam L1 and the measurement light beam L2 is within the coherence length range of the light source 101. By using a low-coherence light source with a coherence length of about several tens of μm for the light source 101, an interference signal is observed when the difference in OPL between the reference light beam L1 and the measurement light beam L2 is within the coherence length range.

[0034] Next, the optical path of the reference light beam L1 will be described. The reference light beam L1 split by the beam splitter 102 is converted into parallel light by the collimator lens 106 and then enters the reflection mirror 111.

[0035] Then, the reference light beam L1 reflected at a right angle by the reflection mirror 111 passes through the beam splitter 104 and enters the reference mirror 112, and is reflected in the direction opposite to the incident direction. At this time, by moving the reference mirror 112 to an arbitrary position along the optical axis of the reference light beam L1, the optical path length of the reference light beam L1 can be changed according to the position of the lens surface to be measured among the lens groups of the optical system M to be inspected.

[0036] The reference light beam L1 reflected by the reference mirror 112 is incident on the beam splitter 104 again, and is reflected by this beam splitter 104 toward the photodetector 113. Then, the reference light beam L1 is incident on the photodetector 113 together with the measurement light beam L2 synthesized by the beam splitter 104.

[0037] Next, the optical path of the measurement light beam L2 will be described. The measurement light beam L2 split by the beam splitter 102 is converted into parallel light by the collimator lens 105, then passes through the beam splitter 103 and is incident on the objective lens 108.

[0038] The reflection detection system 120 is configured to be movable to an arbitrary position along the optical axis of the measurement light beam L2. Thereby, the measurement light beam L2 emitted from the objective lens 108 is focused on a predetermined focal position. The arrangement position of the reflection detection system 120 is obtained in advance by optical calculations such as ray tracing. Thereby, a predetermined position regarding the lens surface to be measured in the optical system M to be inspected, for example, the apparent curvature center position, can be made to coincide with the focal position of the objective lens 108.

[0039] Here, the "apparent curvature center position" refers to the image position of the curvature center position, which is the design value of a specific lens surface, as seen from the objective lens 108 side when measuring a specific lens surface in the optical system M to be inspected. By arranging it in this way, the measurement light beam L2 reflected by a specific lens surface passes through the objective lens 108 again and becomes parallel light within, for example, ±10° with respect to the optical axis of the measurement light beam L2.

[0040] Then, the measurement light beam L2 incident on the beam splitter 103 again is reflected by this beam splitter 103 and focused by the imaging lens 109. Then, the measurement light beam L2 passes through the beam splitter 104 and is incident on the photodetector 113 together with the reference light beam L1 synthesized by the beam splitter 104.

[0041] Next, the positional relationship of each member constituting the imaging optical system 117 of the optical measurement device 100 of the present embodiment will be described. In the optical measurement device 100 of the present embodiment, the objective lens 108 and the imaging lens 109 are arranged such that the position G1 is reached where the rear focal position of the objective lens 108 and the front focal position of the imaging lens 109 that constitute the imaging optical system 117 coincide. Here, the rear focal position is the focal position of the light beam after passing through the lens, and the front focal position is the focal position of the light beam before entering the lens.

[0042] Further, in the optical measurement device 100 of the present embodiment, the imaging lens 109 and the photodetector 113 are arranged such that the rear focal position of the imaging lens 109 that constitutes the imaging optical system 117 becomes the incident surface of the photodetector 113.

[0043] By arranging the objective lens 108, the imaging lens 109, and the photodetector 113 that constitute the imaging optical system 117 at the positions described above, it becomes possible to perform both the surface interval measurement and the eccentricity measurement with high accuracy.

[0044] [Manufacturing method of optical measurement device: First Embodiment] As a manufacturing method of an optical measurement device having the above configuration, an adjustment method during the manufacture of the imaging optical system will be described. FIG. 2 is a schematic configuration diagram showing this adjustment method. During the manufacture of the optical measurement device 100 of the present embodiment, the adjustment method of the imaging optical system 117 is as follows. First, a mirror member 150 having a curved mirror surface 151 with a known curvature is arranged on the rear side of the objective lens 108. Then, after arranging the objective lens 108 such that the focus point of the measurement light beam L2, which is the second light beam, becomes the focus of the mirror surface, the measurement light beam L2 is made to enter the photodetector 113 of the imaging camera 114.

[0045] Next, the parallel light of the reference light beam L1 is made to enter the photodetector 113. Then, while confirming on the monitor 119 connected to the computer 115 so that the number of interference fringes due to the interference between this reference light beam L1 and the measurement light beam L2 becomes zero, the position of the imaging lens 109 is adjusted to adjust the distance between the objective lens 108 and the imaging lens 109.

[0046] Here, as an example of a method for forming the parallel light of the measurement light beam L2, as shown in FIG. 3, the projection index Q1 is moved along the optical axis direction of the measurement light beam L2 to find the reflected image Q2 of the mirror surface 151 (see FIG. 3(a)). Next, the distance from the position along the optical axis direction of the projection index Q1 where this reflected image Q2 is generated to the focal position of the mirror surface 151 is calculated. Then, by moving the projection index Q1 by the calculated distance, the incident measurement light beam L2 can be made into parallel light (see FIG. 3(b)).

[0047] [Optical Measurement Method: First Embodiment] The operation and optical measurement method of the optical measurement apparatus having the configuration of the first embodiment described above will be described. The optical measurement apparatus 100 of the first embodiment has a surface interval measurement mode for measuring the surface interval between the lenses constituting the optical system M to be inspected and an eccentricity measurement mode for measuring the eccentricity of the lenses.

[0048] In the present embodiment, it is assumed that the surface interval measurement mode is first performed, and subsequently, the eccentricity of the lens is measured. First, in the surface interval measurement mode, the optical system M to be inspected is fixed at a predetermined position of the optical measurement apparatus 100. Then, light from the light source 101 is irradiated and made to enter the beam splitter (beam splitting element) 102. Here, the light from the light source that has entered the beam splitter 102 is split into a reference light beam L1 (first light beam) and a measurement light beam L2 (second light beam) (beam splitting step).

[0049] The reference light beam L1 split by the beam splitter 102 is collimated by the collimator lens 106, then reflected by 90° by the reflection mirror 111, passes through the beam splitter (beam combining element) 104, and enters the reference mirror (optical path length variable member) 112. Here, the reference mirror 112 changes the optical path length of the reference light beam L1 by moving its arrangement position along the optical axis direction of the reference light beam L1 according to the position of the optical surface of the lens that is the object of the surface interval measurement of the optical system M to be inspected (optical path length variable step).

[0050] Then, the reference light beam L1 reflected by the reference mirror 112 enters the beam splitter 104 again, where it is combined with the measurement light beam L2 to be described later and enters the photodetector (light intensity detection surface) 113 of the imaging camera (light intensity detection sensor) 114 (beam combining step).

[0051] On the other hand, the measurement light beam L2 split by the beam splitter 102 is collimated by the collimator lens 105, then passes through the beam splitter 103 and enters the objective lens 108. Then, the objective lens 108 makes the measurement light beam L2 enter the lens that is the object of the surface interval measurement in the optical system M to be inspected (condensing step).

[0052] FIG. 4 is a schematic diagram showing the focal position and optical path of the measurement light beam with respect to the lens in the present embodiment. In the present embodiment, for the measurement light beam L2, a focal point (condensing point) is set at a position P2 that is laterally displaced from the curvature center P1 of the measurement target lens F1 onto the optical axis M1. As a result, the measurement light beam L2 is reflected by the inner surface of the measurement target lens F1, and a reflected image is formed at a laterally displaced position P3 on the opposite side of the position P2 on the optical axis M1. Thus, in the present embodiment, the measurement light beam L2 is incident on the measurement target lens F1 at the center of the sphere to perform an equi-magnification measurement.

[0053] Thus, the measurement light beam L2 reflected by the optical system M to be inspected passes through the objective lens 108, is reflected by the beam splitter 103, and enters the imaging lens 109. At this time, in this embodiment, the objective lens 108 and the imaging lens 109 are arranged such that the rear focal position of the objective lens 108 with respect to the measurement light beam L2 that constitutes the imaging optical system 117 coincides with the front focal position of the imaging lens 109 for the measurement light beam L2 at the position G1.

[0054] Since the rear focal position of the objective lens 108 and the front focal position of the imaging lens 109 can be known as design positions, they can be arranged as design positions. However, the rear focal position of the actually manufactured objective lens 108 and the front focal position of the imaging lens 109 do not necessarily coincide with the design value positions due to manufacturing errors.

[0055] For example, the focal lengths of the objective lens 108 and the imaging lens 109 may each deviate from the design values by about 10%. The coincidence of the rear focal position of the objective lens 108 and the front focal position of the imaging lens 109 at the position G1 here means coincidence within the deviation range of the sum of 10% of the design focal length of the objective lens 108 and 10% of the design focal length of the imaging lens 109.

[0056] Then, the measurement light beam L2 that has passed through the imaging lens 109 enters the beam splitter 104, is combined with the reference light beam L1 described above, and then enters the photodetector 113 of the imaging camera 114 (beam combining step).

[0057] The photodetector 113 detects the light intensity distribution of the interference fringes generated by the reference light beam L1 and the measurement light beam L2 (light intensity detection step). Then, based on the of DAL change amount of the reference light beam L1 and the contrast change of the light intensity distribution, the surface interval of the optical system to be inspected is calculated (surface interval calculation step).

[0058] Hereinafter, the principle of high-precision surface interval measurement by equal magnification measurement and spherical center incidence using the optical measurement apparatus of this embodiment will be described. First, the DAL (Dispersion conforming Air Length) will be explained. The DAL is represented by the following formula (1). DAL = Σ (length of optical material × group refractive index) ··· (1) Here, Σ represents the sum of the number of surfaces of the entire optical system through which the light emitted from the light source passes.

[0059] For example, as shown in FIG. 5, when the same single-wavelength light is incident on the measurement optical path (A - B) and the reference optical path (C - D) respectively, interference light (interference fringes) is generated due to the OPL difference. The contrast of such interference fringes changes as the OPL of the reference optical path is changed (moved in the Z direction in FIG. 5). That is, the intensity of the interference light changes with a period of 2πλ as the difference between the OPL of the measurement optical path (A - B) and the OPL of the reference optical path (C - D) changes. Here, the OPL (Optical Path Length) is represented by the following formula (2). OPL = Σ (length of optical material × refractive index) ··· (2)

[0060] Then, as shown in FIG. 6, when white light containing a plurality of wavelength lights is incident on the measurement optical path (A - B) and the reference optical path (C - D) respectively, due to the difference in dispersion between the measurement optical path (A - B) and the reference optical path (C - D), a phase variation occurs for each wavelength of light. And when the DALs of the measurement optical path (A - B) and the reference optical path (C - D) match, the contrast of the interference fringes becomes maximum. In this embodiment, when the contrast of the interference fringes is maximum, the characteristic that the DAL of the measurement system and the DAL of the reference system match is used to calculate the surface interval of the lens.

[0061] In the optical measurement device 100 of this embodiment, the objective lens 108 and the imaging lens 109 are arranged such that the rear focal position of the objective lens 108 with respect to the measurement light beam L2 constituting the imaging optical system 117 coincides with the front focal position of the measurement light beam L2 of the imaging lens 109 at the position G1 (see FIG. 1). Also, the imaging lens 109 and the photodetector 113 are arranged such that the rear focal position of the imaging lens 109 constituting the imaging optical system 117 becomes the incident surface of the photodetector 113

[0062] As a result, even in the case of an equal magnification measurement and centered incidence in which the measurement light beam L2 is reflected by the inner surface of F1 that enters the lens to be measured shown in Fig. 4 and a reflected image is formed at a laterally displaced position P3 on the opposite side of the position P2 on the optical axis M1, the DAL coincides between the optical path of the reference light beam L1 and the optical path of the measurement light beam L2.

[0063] For example, even in the case of an equal magnification measurement and centered incidence in which the measurement light beam L2 is made incident so as to be focused on a position P2 that is laterally displaced from the curvature center P1 of the lens to be measured F1 onto the optical axis M1 as shown in Fig. 4, even if the reflected image is laterally displaced due to the eccentricity of the lens to be measured F1 and the measurement light beam L2 traveling toward the photodetector 113 passes outside the optical axis, the OPL does not change between the light beam passing through the optical axis.

[0064] Fig. 7 is a schematic diagram showing the optical path and the equiphase surface to the imaging surface (photodetector) when the rear focal position of the objective lens and the front focal position of the imaging lens are made to coincide. According to such Fig. 7, the OPL coincides between the reflected image without lateral displacement (solid line) and the reflected image with lateral displacement (dashed line). If the OPL coincides, the DAL also almost coincides. As a result, in the case of an equal magnification measurement and centered incidence in which lateral displacement occurs as used for lens eccentricity measurement, the measurement between lens surfaces can be performed with high precision.

[0065] The computer 115 detects, for example, based on the reflected image (interference fringes) detected by the photodetector 113 as shown in Fig. 8, the position of the reference mirror at which the contrast of the interference fringes is maximized with a length measuring device and converts it into an interfacial spacing.

[0066] When there is a lateral displacement of the reflected image in the measurement of the lens surface interval, the DAL of the measurement light beam L2 changes according to the lateral displacement, and the surface interval measurement result also changes. Therefore, when performing high-precision surface interval measurement, it is preferable to perform it by magnification measurement or surface vertex incidence under the condition that the reflected image does not have a lateral displacement. However, there was a problem that the decentration measurement of the lens could not be performed under this condition. In the optical measurement apparatus 100 of the present embodiment, even in the case of magnification measurement and spherical center incidence where the reflected image has a lateral displacement, it is possible to measure the surface interval of the lens of the optical system M to be inspected with high precision. That is, the surface interval measurement and decentration measurement of the lens can be performed with high precision and efficiently.

[0067] Next, the optical measurement apparatus 100 shifts to the decentration measurement mode and measures the decentration amount of the lens of the optical system M to be inspected. In the decentration measurement, the optical path of the reference light beam L1 is not used. For this reason, in the decentration measurement mode, the beam splitter 102 may be retracted from the optical path so that all the light from the light source 101 becomes the measurement light beam L2 and is incident on the collimator lens 105, or a shutter or the like may be provided on the optical path of the reference light beam L1 to block the optical path of the reference light beam L1.

[0068] Even in the decentration measurement mode, the optical measurement apparatus 100 measures the decentration amount of the lens with magnification measurement and spherical center incidence with respect to the lens of the optical system M to be inspected, similar to the surface interval measurement mode. In the decentration measurement mode, the measurement light beam L2, which is the light from the light source 101, is irradiated, made parallel by the collimator lens 105, and then incident on the objective lens 108 via the beam splitter 103. Then, the measurement light beam L2 is incident on each lens constituting the optical system M to be inspected by the objective lens 108.

[0069] For example, as shown in FIG. 4, a focus (projection index) is set at a position P2 laterally displaced from the curvature center P1 of the lens F1 to be measured on the optical axis M1. As a result, the measurement light beam L2 is reflected by the inner surface of the lens F1 to be measured, and a reflected image is formed at a laterally displaced position P3 on the opposite side of the position P2 on the optical axis M1.

[0070] A measurement light beam L2 including a reflected image shifted horizontally from such projection indices is made incident on a photodetector 113 through an imaging lens 109. A computer 115 calculates the amount of deviation of the horizontally shifted reflected image detected by the photodetector 113.

[0071] The reflected image detected by the photodetector 113 is displayed, for example, at a position corresponding to the amount of eccentricity as shown in FIG. 9 as reflected image I. i The amount of deviation of such a reflected image is measured from the first surface to the final surface of the lens constituting the optical system M to be measured, and each lens eccentricity is measured.

[0072] According to the optical measuring device and the optical measuring method of the present embodiment configured as described above, at the time of measuring the surface interval, measurement is performed with equal magnification measurement and spherical center incidence of the measurement light beam similar to the case of measuring the eccentricity amount. Even when a horizontal shift occurs, high-precision surface interval measurement equivalent to the case where measurement is performed under the condition of no horizontal shift with equal magnification measurement and surface vertex incidence can be performed without degrading the measurement accuracy. Further, by using a single incident method such as equal magnification measurement and spherical center incidence for the incident method of the measurement light beam with respect to the lens both at the time of surface interval measurement and at the time of eccentricity measurement, it becomes possible to continuously perform surface interval measurement and eccentricity measurement in a short time without significantly changing the settings with one measuring device.

[0073] [Optical Measuring Method: Modification Example of the First Embodiment] In the optical measuring method described above, at the time of surface interval measurement and eccentricity measurement, a focus (projection index) of the measurement light beam is formed on the optical axis at the apparent curvature center position of the lens, and equal magnification measurement is performed to form a reflected image at a horizontally shifted position on this optical axis. However, in addition to this, the optical measuring method of the present invention is also applicable to unequal magnification measurement in exactly the same manner.

[0074] As shown in FIG. 10, in unequal magnification measurement, the converging point of the measurement light beam L2 incident on the lens F2 to be measured is set at a position P5 shifted in the optical axis direction from the curvature center P4.

[0075] Then, the reflected image of this measurement light beam L2 is formed at a position P6 that is displaced in the optical axis direction from the curvature centers P4 and P5. At this time, the interval L in the optical axis direction between the position P5 and the position P6 along the incident direction of the measurement light beam L2 is defined as the magnification ratio.

[0076] Conventionally, such a non-uniform magnification measurement is a condition where the reflected image is laterally displaced. Since the DAL of the measurement light beam L2 changes according to the lateral displacement and the surface interval measurement result also changes, it has not been possible to perform surface interval measurement with high precision. However, according to the optical measurement method of the present embodiment described above, it is possible to perform surface interval measurement with high precision even in non-uniform magnification measurement.

[0077] [Method for manufacturing an optical measurement device: Second Embodiment] In the method for manufacturing an optical measurement device of the present embodiment, in the optical measurement device 100 shown in FIG. 1, when manufacturing the imaging optical system 117, when the distribution of the OPL in the measurement light beam (second light beam) L2 on the photodetector (light intensity detection surface) 113 coincides with the distribution of the OPL of the reference light beam (first light beam) L1 on the photodetector 113, it is manufactured so that the distribution of the DAL in the measurement light beam L2 on the photodetector 113 coincides with the distribution of the DAL of the reference light beam L1 on the photodetector 113.

[0078] In the first embodiment of the method for manufacturing an optical measurement device described above, the objective lens 108 and the imaging lens 109 are arranged so that the rear focal position of the objective lens 108 and the front focal position of the imaging lens 109 coincide, and the OPL distribution is set to 0 within the imaging surface imaged by the photodetector 113. Here, the OPL distribution refers to the difference in OPL within the imaging surface as the OPL distribution.

[0079] However, as described above, even if the arrangement positions of the objective lens 108 and the imaging lens 109 are adjusted so that the OPL distribution becomes zero, if the lateral displacement amount of the reflected image formed on the measurement lens becomes large, there is a possibility that the error in the surface interval measurement value will become large even in the optical measurement method of the first embodiment. This is because, as shown in FIG. 11, in the measurement of the surface interval of a lens using the principle of low coherence interference, it is the DAL, not the OPL, that determines the maximum position of the contrast of the interference fringes, and even if the OPL distribution is made zero, the DAL distribution does not necessarily become zero. Here, the DAL distribution refers to the difference in DAL within the imaging plane as the DAL distribution.

[0080] Therefore, as in the manufacturing method of the optical measurement apparatus of the present embodiment, when the distribution of the OPL in the measurement light beam L2 on the photodetector 113 coincides with the distribution of the OPL of the reference light beam L1 on the photodetector 113, by making the distribution of the DAL of the measurement light beam L2 on the photodetector 113 coincide with the distribution of the DAL of the reference light beam L1 on the photodetector 113, the error in the surface interval measurement value can be suppressed.

[0081] As a method of making the distribution of the DAL in the measurement light beam L2 coincide with the distribution of the DAL of the reference light beam L1, as shown in FIG. 12, by optically designing the RDN of the imaging lens 109, the distribution of the DAL of the measurement light beam L2 and the distribution of the DAL of the reference light beam L1 can be made to coincide. By optically designing the RDN of the objective lens 108 as well, the distribution of the DAL of the measurement light beam L2 and the distribution of the DAL of the reference light beam L1 can be made to coincide.

[0082] In the present embodiment, as described above, by manufacturing the optical measurement apparatus 100 using the imaging lens 109 and the objective lens 108 in which the RDN is optically designed so that the distribution of the DAL in the measurement light beam L2 coincides with the distribution of the DAL of the reference light beam L1, an optical measurement apparatus 100 capable of performing surface interval measurement with higher accuracy can be realized.

[0083] [Optical Measurement Apparatus: Second Embodiment] Next, the optical measurement apparatus of the second embodiment of the present invention will be described. Note that the same components as those of the optical measurement apparatus of the first embodiment are denoted by the same reference numerals, and redundant descriptions are omitted. FIG. 13 is a schematic configuration diagram showing an example of the optical measurement apparatus of the present invention. The optical measurement apparatus 200 includes a light source 101, a beam splitter (light beam splitting element) 102, a beam splitter 103, a beam splitter (light beam combining element) 104, collimator lenses 105 and 106, a condenser lens (condensing element) 107, an objective lens 108, an imaging lens 109, a reflection mirror 111, a reference mirror (optical path length variable member) 112, an imaging camera (light intensity detection sensor) 114 provided with a photodetector (light intensity detection surface) 113, and a computer (inter-surface distance detection processor) 115.

[0084] Further, on the optical path of the objective lens 108, a DUT optical system M having a plurality of optical surfaces, which is a measurement object, is disposed. The DUT optical system M has a lens group composed of a plurality of lenses.

[0085] Among these members constituting the optical measurement apparatus 200, the objective lens 108, the imaging lens 109, and the photodetector 113 constitute an imaging optical system 217.

[0086] Next, the positional relationship of each member constituting the imaging optical system 217 of the optical measurement apparatus 200 of the present embodiment will be described.

[0087] The imaging optical system 217 is adjusted so that an interference fringe due to interference between a measurement light beam (second light beam) and a reference light beam (first light beam) L1 is observed. That is, the objective lens 108 and the imaging lens 109 are arranged such that the rear focal position G2 of the objective lens 108 and the front focal position G3 of the imaging lens 109 constituting the imaging optical system 117 are intentionally formed with a predetermined interval Δt therebetween. Note that the rear focal position G2 of the imaging lens coincides with the photodetector 113.

[0088] By adopting such a configuration, even without using a special objective lens or imaging lens with an RDN optical design that aligns the DAL distribution in the measurement light beam L2 with the DAL distribution of the reference light beam L1 when the horizontal displacement amount of the reflected image formed on the lens to be measured in the DUT optical system M increases, it is possible to eliminate the difference in the DAL distribution by using an objective lens 108 or an imaging lens 109 with a general optical design such as a commercially available lens. The adjustment method during the manufacture of such an imaging optical system 217 will be described in the manufacturing method of the optical measurement apparatus according to the following embodiment.

[0089] [Manufacturing Method of Optical Measurement Apparatus: Third Embodiment] In the manufacturing method of the optical measurement apparatus according to the present embodiment, in the optical measurement apparatus 200 shown in FIG. 13, during the manufacture of the imaging optical system 117, first, the number of interference fringes generated when the DAL distribution up to the photodetector 113 of the measurement light beam L2 coincides with the DAL distribution up to the photodetector 113 of the reference light beam L1 is examined in advance.

[0090] The method of examining the number of such interference fringes in advance utilizes the fact that the DAL distribution changes depending on the arrangement position of the imaging lens 109, examines the position of the imaging lens 109 that coincides with the DAL distribution of the reference light beam L1 by simulation using a computer or the like, and calculates the number of interference fringes detected by the photodetector 113 from the OPL distribution of the measurement light beam L2 in that state.

[0091] Next, as shown in FIG. 2, a mirror member 150 having a curved mirror surface 151 with a known curvature is arranged on the rear side of the objective lens 108. Then, after arranging the objective lens 108 so that the focus point of the measurement light beam L2 becomes the focus of the mirror surface, the measurement light beam L2 is made incident on the photodetector 113 of the imaging camera 114.

[0092] Then, the distance between the objective lens 108 and the imaging lens 109 is adjusted so that the number of interference fringes detected by the photodetector 113 with the measurement light beam L2 and the reference light beam L1 matches the number of interference fringes calculated in advance by the above-described calculation. Such adjustment can be realized, for example, by moving the imaging lens 109 along the optical axis. At this time, the photodetector 113 is adjusted together with the imaging lens so as to coincide with the rear focal position G2 of the imaging lens.

[0093] By such adjustment during the manufacture of the imaging optical system 117, as shown in FIG. 14, even if the OPL distributions do not match between the measurement light beam L2 and the reference light beam L1, the DAL distributions can be made to match.

[0094] By performing the adjustment during the manufacture of the imaging optical system 117 as described above, without using a special objective lens or imaging lens with an RDN optical design that makes the DAL distribution in the measurement light beam L2 match the DAL distribution of the reference light beam L1, the difference in the DAL distribution can be eliminated by using a general optical design objective lens 108 or imaging lens 109 such as a commercially available lens.

[0095] As shown in FIG. 15, such a method for manufacturing an optical measurement apparatus according to the present embodiment can also calculate the number of interference fringes generated in advance even when the DAL distribution and the OPL distribution of the reference light beam L1 do not match those of the measurement light beam L2, and adjust the distance between the objective lens 108 and the imaging lens 109 so that the number of interference fringes that matches the calculated number of interference fringes is generated, thereby realizing the optical measurement apparatus 200.

[0096] Although the embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalent scope thereof.

Explanation of Reference Numerals

[0097] 100…Optical measurement device 101…Light source 102, 103, 104…Beam splitter 105, 106…Collimator lens 107…Condensing lens (condensing element) 108…Objective lens 109…Imaging lens 111…Reflection mirror 112…Reference mirror (optical path length variable member) 113…Photoelectric detector (light intensity detection surface) 114…Imaging camera (light intensity detection sensor) 115…Computer (surface interval detection processor) 117…Imaging optical system 120…Reflection detection system M…Optical system under test L1…Reference beam (first beam) L2…Measurement beam (second beam)

Claims

1. An optical measuring device for measuring the lens surface intervals and lens eccentricities of an optical system under test having a plurality of optical surfaces, a beam splitting element that splits light from a light source with a short coherence distance into a first light beam and a second light beam, an optical path length variable member that changes the optical path length of the first light beam according to the position of the optical surface to be measured, a condensing element that condenses the second light beam at a predetermined position related to the optical surface to be measured among the optical system under test disposed in the optical path of the second light beam, a beam combining element that overlaps the first light beam with a changed optical path length and the second light beam reflected by the optical surface to be measured, a light intensity detection sensor that detects the light intensity distribution of interference fringes generated by the first light beam and the second light beam with a light intensity detection surface, a surface interval calculation processor that calculates the surface interval of the optical system under test based on the change amount of the DAL of the first light beam and the contrast change of the light intensity distribution, an imaging optical system that forms an image of an image generated by reflection of the second light beam on the optical surface on the light intensity detection surface, and is provided with: the imaging optical system has an objective lens, an imaging lens, and the light intensity detection surface, An optical measuring device, characterized in that the rear focal point of the objective lens coincides with the front focal point of the imaging lens, and the rear focal point of the imaging lens coincides with the light intensity detection surface. Here, DAL (Dispersion conforming Air Length) is defined by the following formula (1). DAL = Σ (refractive material length × group refractive index) ··· (1) Here, Σ represents the sum of the number of surfaces of the entire optical system through which the light emitted from the light source passes.

2. A method for manufacturing the optical measuring device according to claim 1, When manufacturing the imaging optical system, the condensing point of the second light beam is arranged at the focus of a mirror surface with a known curvature, and the position of the imaging lens is adjusted so that the interference fringes due to the interference between the first light beam and the second light beam become zero by illuminating the light intensity detection surface with parallel light, A method for manufacturing an optical measuring device, comprising a step of adjusting the interval between the objective lens and the imaging lens.

3. A method for manufacturing the optical measuring device according to claim 1, A method for manufacturing an optical measurement device, characterized in that when, during the manufacture of the imaging optical system, the distribution of the OPL in the second light beam on the light intensity detection surface coincides with the distribution of the OPL of the first light beam on the light intensity detection surface, the distribution of the DAL in the second light beam on the light intensity detection surface coincides with the distribution of the DAL of the first light beam on the light intensity detection surface. Here, OPL (Optical Path Length) is defined by the following formula (2). OPL = Σ (material length × refractive index) ··· (2)

4. An optical measurement method for measuring the lens surface interval and lens decentration amount of an optical system under test having a plurality of optical surfaces, a light beam splitting step of splitting light from a light source with a short coherence distance into a first light beam and a second light beam; an optical path length variable step of changing the optical path length of the first light beam according to the position of the optical surface to be measured; a light condensing step of condensing the second light beam at a predetermined position related to the optical surface to be measured among the optical systems under test arranged in the optical path of the second light beam; a light beam combining step of superposing the first light beam with a changed optical path length and the second light beam reflected by the optical surface to be measured; a light intensity detection step of detecting the light intensity distribution of the interference fringes generated by the first light beam and the second light beam by a light intensity detection surface; including a surface interval calculation step of calculating the surface interval of the optical system under test based on the change amount of the DAL of the first light beam and the contrast change of the light intensity distribution; an imaging optical system having an objective lens, an imaging lens, and a light intensity detection surface forms an image of an image generated by reflection of the second light beam on the optical surface on the light intensity detection surface; characterized in that the rear focal point of the objective lens is made to coincide with the front focal point of the imaging lens, and the rear focal point of the imaging lens is made to coincide with the light intensity detection surface.

5. An optical measurement device for measuring the lens surface interval and lens decentration amount of an optical system under test having a plurality of optical surfaces, a light beam splitting element that splits light from a light source with a short coherence distance into a first light beam and a second light beam; an optical path length variable member that changes the optical path length of the first light beam according to the position of the optical surface to be measured; a light condensing element that condenses the second light beam at a predetermined position related to the optical surface to be measured among the optical systems under test arranged in the optical path of the second light beam; A beam combining element that superimposes the first light beam with a changed optical path length and the second light beam reflected by the optical surface to be measured; An optical intensity detection sensor that detects the light intensity distribution of interference fringes generated by the first light beam and the second light beam with an optical intensity detection surface; A surface interval calculation processor that calculates the surface interval of the optical system under test based on the change amount of the DAL of the first light beam and the contrast change of the light intensity distribution; An imaging optical system that forms an image of an image generated by reflection of the second light beam on the optical surface on the optical intensity detection surface, and includes: The imaging optical system has an objective lens, an imaging lens, and the optical intensity detection surface; The rear focal point of the objective lens coincides with the front focal point of the imaging lens, and the rear focal point of the imaging lens coincides with the optical intensity detection surface; In the imaging optical system, the number of interference fringes generated when the DAL distribution of the second light beam up to the optical intensity detection surface coincides with the DAL distribution of the first light beam up to the optical intensity detection surface is examined in advance, the focus point of the second light beam is arranged at the focus of a mirror surface with a known curvature, the optical intensity detection surface is illuminated with parallel light, and the distance between the objective lens and the imaging lens is adjusted so that the same number of interference fringes as the number of interference fringes examined in advance is observed due to the interference between the first light beam and the second light beam. An optical measurement device characterized by this.

6. A method for manufacturing the optical measurement device according to claim 5, comprising: In the manufacturing of the imaging optical system, a step of examining in advance the number of interference fringes generated when the DAL distribution of the second light beam up to the optical intensity detection surface coincides with the DAL distribution of the first light beam up to the optical intensity detection surface; A step of arranging the focus point of the second light beam at the focus of a mirror surface with a known curvature and illuminating the optical intensity detection surface with parallel light; A step of adjusting the distance between the objective lens and the imaging lens so that the same number of interference fringes as the number of interference fringes examined in advance is observed due to the interference between the first light beam and the second light beam. A method for manufacturing an optical measurement device characterized by including this.

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