Optical device, evaluation device, evaluation method, and method for manufacturing optical system

Abstract

To provide an optical device that can simply evaluate an optical performance of various optical systems.SOLUTION: An optical device has: a first light source (120); a chart (121) that guides light from the first light source to an inspected optical system (130); a second light source (110) that is different from the first light source; an optical system (111, 112 and 113) that forms a point image by light from the second light source; and a light reception system (140 and 151) that receives first light from the chart via the inspected optical system, and second light from the point image via the inspected optical system, in which the first light and second light are incident upon a mutually different position in the inspected optical system.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical device, an evaluation device, an evaluation method, and a method for manufacturing an optical system. [Background technology]

[0002] Patent Document 1 discloses a method for measuring the MTF (Modulation Transfer Function) at multiple image heights from light emitted from a chart illuminated by a light source. By using this method, the amount of one-sided blur can be obtained from the MTF, and the imaging optical system can be adjusted to reduce the amount of one-sided blur.

[0003] Patent Document 2 discloses a method in which light emitted from a high-intensity point light source is transmitted through an imaging optical system and the transmitted wavefront is acquired by a wavefront sensor. Using this method, basic aberrations of the imaging optical system, such as spherical aberration, coma aberration, astigmatism, field curvature, and one-sided blur, can be acquired from on-axis and off-axis wavefront aberrations. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-212620 [Patent Document 2] Japanese Patent Application Publication No. 2019-066428 Summary of the Invention [Problem to be solved by the invention]

[0005] The method disclosed in Patent Document 1 can measure the MTF at multiple image heights of various optical systems, but can only obtain part of the aberration (optical performance) (one-sided blur and field curvature).The method disclosed in Patent Document 2 can measure on-axis and off-axis wavefront aberration, but in order to measure imaging optical systems with different specifications such as angle of view and sensor size, it is necessary to change the positions of the sensor and light source.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an optical device, an evaluation device, an evaluation method, and a method for manufacturing an optical system that are capable of easily evaluating the optical performance of various optical systems. [Means for solving the problem]

[0007] An optical device according to one aspect of the present invention includes a first light source and a second light source, a chart that guides light from the first light source to an optical system under test, an optical system that forms a point image using light from the second light source, and a light-receiving system that receives first light from the chart via the optical system under test and second light from the second light source via the optical system under test, the chart has a light-shielding portion and an opening surrounded by the light-shielding portion, and the optical system forms the point image at the opening, The first light and the second light are incident at different positions in the test optical system, and when the numerical aperture of the test optical system is NA and the wavelength of the second light is λ, the size of the point image is smaller than λ / NA.

[0008] Other objects and features of the present invention are illustrated in the following examples. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an optical device, an evaluation device, an evaluation method, and a method for manufacturing an optical system that are capable of easily evaluating the optical performance of various optical systems. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of an evaluation device in Example 1. [Figure 2] FIG. 2 is an explanatory diagram of an SHS according to the first embodiment. [Figure 3] FIG. 1 is a diagram showing the structure of a chart in the first embodiment. [Figure 4] FIG. 1 is a diagram showing a chart pattern in Example 1. [Figure 5] FIG. 2 is an explanatory diagram of an evaluation device in the first embodiment. [Figure 6] FIG. 10 is a schematic diagram of an evaluation device in Example 2. [Figure 7]FIG. 10 is a schematic diagram of an evaluation device as a modified example of the second embodiment. [Figure 8] 10 is a flowchart of a method for manufacturing an optical system according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. [Example]

[0012] First, an evaluation device (measurement device) according to a first embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 is a schematic diagram of an evaluation device 100 according to this embodiment. The evaluation device 100 is an evaluation device that evaluates the optical performance of an optical system to be tested by transmitting light from a light projection system through the optical system to be tested and then receiving the light with a light receiving system, and is capable of evaluating (measuring) the on-axial transmitted wavefront and off-axial MTF of various optical systems to be tested.

[0013] The evaluation device 100 includes an optical device having a light projection system that projects light onto a test lens (test optical system) 130 and a light receiving system that receives light from the test lens 130, and a PC (control unit) 160. The light projection system includes a laser light source (second light source) 110, a fiber 111, collimator lenses 112 and 113, a ring light source (first light source) 120, a chart 121, and a stage 122. The ring light source 120 is ring-shaped to form an opening that transmits light from the laser light source 110. The light receiving system includes an intensity sensor (light intensity sensor) 140, a collimator lens 150, and an Shack-Hartmann sensor (SHS) 151 as a wavefront sensor. The PC 160 controls each component of the optical device. The test lens 130 is an imaging optical system consisting of multiple optical elements, and is arranged so that the chart 121 and the intensity sensor 140 form an object-image relationship.

[0014] First, a system for measuring the on-axis transmitted wavefront of the lens under test 130 will be described. Light 10 emitted from a laser light source 110 via a fiber 111 is converted into parallel light by a collimator lens 112, and then condensed at the focal position of the lens under test 130 via a collimator lens 113. The condensed light becomes a pseudo-point light source at the focal position of the lens under test 130, then becomes divergent light 11, and enters the lens under test 130. The divergent light 11 becomes convergent light 12 via the lens under test 130, and after condensing, becomes divergent light again and enters the collimator lens 150. The light that has been converted into approximately parallel light by the collimator lens 150 is imaged by an SHS 151. The signal acquired by the SHS 151 is calculated by a PC 160.

[0015] Next, referring to FIG. 2, a case where the wavefront of incident light is measured by the SHS 151 will be described. FIG. 2 is an explanatory diagram of the SHS 151, showing a cross section of the SHS 151 when measuring the wavefront of incident light. The incident light is split by the microlens array 152 in FIG. 2 and focused on the CMOS sensor 153 located behind it. The light focused on the CMOS sensor 153 is analyzed by the PC 160 shown in FIG. 1. The tilt of the wavefront of the incident light is calculated from the position of the center of gravity of the focusing point, and the shape of the wavefront of the incident light is determined by integrating or fitting the data group of the wavefront tilt.

[0016] To accurately determine the transmitted wavefront of the lens 130 under test, an ideal spherical wave emitted from a point light source smaller than the size defined by the following formula (1) is made incident on the lens 130 under test. In formula (1), λ is the wavelength of the laser light source 110, and NA is the numerical aperture of the lens 130 under test.

[0017]

number

[0018] To form a point light source at the focal position of the lens under test 130, the NA of the collimator lens 113 must be larger than the NA of the lens under test 130. The laser light source 110 is a high-intensity light source that has coherence that allows it to be focused to a size equal to or smaller than the size of equation (1) and a light amount that can be measured by the SHS 151. Examples of such light sources include gas lasers and semiconductor lasers. Light focused with a sufficiently large NA from a light source with high coherence can be considered a pseudo-point light source for the lens under test 130.

[0019] Next, a system for measuring the off-axis MTF of the lens under test 130 will be described. Light emitted from the ring light source 120 in Fig. 1 passes through the transmission section (passing section) of the chart 121 and enters the lens under test 130 as divergent light rays 21 and 31. After passing through the lens under test 130, the divergent light rays 21 and 31 become converging light rays 22 and 32 and are received by the intensity sensor 140. The intensity sensor 140 can be driven by a stage (not shown).

[0020] FIG. 3 is a structural diagram of the chart 121. An opening 1211 that transmits light from the laser light source 110 is formed in the center of the chart 121, and the light emitted from the laser light source 110 passes through. Absorbing portions 1212 and transmitting portions (passing portions) 1213 are provided around the periphery of the chart 121, and a diffuser 1214 is disposed upstream of the transmitting portions 1213. The diffuser 1214 is provided to uniform the light distribution characteristics of the light from the ring light source 120. As described above, in this embodiment, the chart 121 has a plurality of transmitting portions 1213 and absorbing portions 1212, and the point light source generated by the laser light source 110 is disposed in one of the plurality of transmitting portions 1213 (opening 1211). Furthermore, in this embodiment, the diffuser 1214 is disposed between the ring light source 120 and a transmitting portion (other than the passing portion) of the plurality of transmitting portions 1213 other than the transmitting portion where the point light source is disposed. In this embodiment, the transmitting portions 1213 are air, but this is not limiting, and a transmitting portion that transmits light may be provided. In this embodiment, the transmitting portions 1213 of the chart 121 are collectively called a chart pattern or a pattern.

[0021] If the light from the ring light source 120 overlaps with the divergent light 11 from the laser light source 110, it will lead to a measurement error. To avoid this overlap, a light-shielding portion 1215 may be provided as shown in FIG. 3. However, this embodiment is not limited to this, and the light-shielding portion may be provided in a location other than the chart 121 as long as the configuration can avoid overlapping between the light from the ring light source 120 and the divergent light 11 from the laser light source 110. Alternatively, instead of providing a light-shielding portion, the PC 160 may turn off the ring light source 120 while the SHS 151 is receiving light. This makes it possible to separate the two lights even without a light-shielding portion.

[0022] 4(a) to (c) are diagrams showing the patterns of the chart 121. FIG. 4(a) shows an edge pattern, (b) a slit pattern, and (c) a grid pattern. The MTF value can be calculated from the degree of blur of the chart image. In addition, by defocusing the chart 121 using the stage 122, the defocus characteristics of the MTF value can be obtained.

[0023] As described above, the light projection system includes a first light projection system that forms the light emitted from the chart 121 illuminated by the ring light source 120, and a second light projection system that forms a point light source by shaping the light from the laser light source 110. The intensity sensor 140 receives the light from the first light projection system that has passed through the lens 130 under test, and the SHS 151 receives the light from the second light projection system that has passed through the lens 130 under test.

[0024] These two types of projection systems make it possible to obtain the on-axis transmitted wavefront and off-axis MTF of the test lens 130. The on-axis transmitted wavefront can be resolved into aberration components by fitting the wavefront shape with Zernike polynomials, for example. The fitted Zernike coefficients contain information similar to basic aberrations such as astigmatism, coma, and spherical aberration, as shown in the following equation (2).

[0025] Z4 term = defocus component Z5 term = 0-90° astigmatism component Z6 term = 45° astigmatism component Z7 term = horizontal coma aberration component Z8 term = vertical coma aberration component Z9 term = spherical aberration component Furthermore, the amount of one-sided blur of the test lens 130 can be calculated from the variation in the peak position of the off-axis MTF, and the amount of field curvature of the test lens 130 can be calculated from the peak position of the off-axis MTF and the defocus term of the Zernike polynomial. In this way, the basic aberration of the test lens 130 can be obtained.

[0026] Next, referring to FIG. 5, a case where a test lens (test optical system) 131 having different optical specifications is measured using the evaluation device 100 will be described. FIG. 5 is an explanatory diagram of the evaluation device 100. For example, when measuring test lenses 131 with different focal lengths, the distance from the test lens 131 to the intensity sensor 140 or the SHS 151 is adjusted. When measuring test lenses 131 with different angles of view, the intensity sensor 140 is moved so that it is positioned at the position of the angle of view calculated from the image height and focal length. When measuring MTFs at different image heights, the intensity sensor 140 is positioned so that it measures light emitted from patterns at different image heights, such as light 23, 24, 33, and 34 in FIG. 5. In this case, it is preferable to arrange patterns at multiple image heights on the chart 121, as shown in FIG. 4(a), because this allows the test lens 131 to be replaced without changing the chart 121.

[0027] As described above, the optical device of this embodiment includes a first light source (ring light source 120), a chart 121 that guides light from the first light source to a test optical system (test lens 130), and a second light source (laser light source 110) different from the first light source. The optical device also includes an optical system (fiber 111, collimator lenses 112 and 113) that forms a point image using light from the second light source. The optical device also includes a light-receiving system (intensity sensor 140, SHS 151) that receives the first light from the chart via the test optical system and the second light from the point image via the test optical system. The first light and the second light are incident on different positions in the test optical system.

[0028] The evaluation device 100 of this embodiment includes an optical device and a control unit (PC 160) that evaluates the optical performance of the optical system under test using the output from the light receiving system. Here, the different positions of the optical system under test are, for example, on-axis (center) and off-axis (periphery), but the laser light does not have to be on-axis. Preferably, the optical performance is the frequency response characteristic (MTF) at the position of the chart in the first light projection system and the wavefront aberration at the position of the point light source in the second light projection system.

[0029] The evaluation device 100 has a light intensity sensor that receives first light and a wavefront sensor that receives second light, and executes the steps of receiving, with the wavefront sensor, light that is emitted as a point image and transmitted through the optical system to be tested, and calculating the wavefront aberration of the optical system to be tested from the light received by the wavefront sensor. However, this embodiment is not limited to this, and the evaluation device may have a light intensity sensor that receives the first light and the second light. In this case, the evaluation device includes the steps of receiving, with the light intensity sensor, light that is emitted as a point image and transmitted through the optical system to be tested at a plurality of focus positions, and calculating the wavefront aberration of the optical system to be tested from the plurality of light received at the plurality of focus positions.

[0030] According to this embodiment, it is possible to provide an optical device, an evaluation device, and an evaluation method that can easily evaluate the optical performance of various optical systems. [Example]

[0031] Next, an evaluation device (measurement device) in Example 2 of the present invention will be described with reference to Fig. 6. Fig. 6 is a schematic diagram of an evaluation device 200 in this example.

[0032] The evaluation device 100 includes an optical device having a light projection system that projects light onto a lens under test (optical system under test) 132 and a light receiving system that receives light from the lens under test 132, as well as a PC (controller) (not shown). The light projection system includes a laser light source (second light source) (not shown), a fiber 111, collimator lenses 112 and 113, a chart 123, a beam splitter 201, a reflecting mirror 203, and an LED light source (first light source) 204. The LED light source 204 is configured by arranging multiple LEDs so as to form an opening that transmits light from the laser light source. The light receiving system includes a wavefront sensor 202, a collimator lens 205, and an intensity sensor (light intensity sensor) 206. The lens under test 132 is an imaging optical system made up of multiple optical elements, and is arranged so that the chart 123 and infinity are conjugate to each other.

[0033] Light emitted from a laser light source (not shown) via a fiber 111 forms a point light source (pseudo point light source) at the opening of the chart 123, as in the first embodiment. The light diverging from the pseudo point light source passes through the test lens 132, is reflected by a reflecting mirror 203, and then returns to the collimator lens 113 via the same path. The light returning to the collimator lens 113 is then reflected by a beam splitter 201 and acquired by a wavefront sensor 202. The wavefront sensor 202 is, for example, an SHS, but is not limited to this and may also be a shearing interferometer or a Talbot interferometer.

[0034] Light emitted from the LED light source 204 is passed through a light guide including a fiber or the like and illuminates the chart 123. The illuminated light passes through the transparent portion of the chart 123, is transmitted through the test lens 130, becomes approximately parallel light, passes through a collimator lens 205, and is then received by an intensity sensor 206. A light guide may be provided for each transparent portion of the chart 123, or one light guide may be used to illuminate multiple transparent portions.

[0035] Like the chart 121, the chart 123 has a diffuser plate arranged on a pattern for MTF measurement. The opening of the chart 123 only needs to be located within the image plane of the lens 132 under test, and does not need to be located on the optical axis. If the opening is not located on the optical axis, the shape of the exit pupil of the lens 132 under test may not be circular. In this case, the coefficients may be found for an elliptical shape using a Zernike ellipse. An orthogonalization function tailored to the exit pupil shape may also be used using the Gram-Schmitt concept.

[0036] If the chart 123 is a grid pattern, the intensity sensor 206 always measures the contrast of the pattern at a specific frequency and a specific defocus. By tilting the pattern or the intensity sensor, the defocus characteristics can be obtained within the area of the intensity sensor 206.

[0037] In the evaluation device 200, if light from the LED light source 204 enters the wavefront sensor 202, it will cause an error. To reduce the error, a diffuser may be positioned away from the opening to prevent diffused light from the diffuser from entering the opening. Alternatively, a light-shielding portion surrounding the optical path of the laser light may be provided. That is, at least one of the first and second projection systems may be provided with a light-shielding portion that separates the light from the first and second projection systems. Alternatively, the LED light source 204 may be turned off while the wavefront sensor 202 is receiving light. When a light-shielding portion surrounding the optical path of the laser light between the collimator lens 113 and the chart 123 is provided, the outer surface of the light-shielding portion may be mirror-finished to reflect the light from the LED light source 204 and improve light utilization efficiency.

[0038] Next, a modified example of the evaluation device in this embodiment will be described with reference to Fig. 7. Fig. 7 is a schematic diagram of an evaluation device 210 as a modified example of this embodiment. The evaluation device 210 has a fiber 111, a chart 124, an intensity sensor (light intensity sensor) 211, and a stage 212. The test lens 133 is an imaging optical system made up of multiple optical elements, and is arranged so that the chart 124 and the intensity sensor 211 have an object-image relationship.

[0039] The chart 124 is a black-and-white chart consisting of absorbing portions (black) and scattering portions (white), and is illuminated by a light source (first light source) not shown. The first light source is an illumination light source such as a fluorescent lamp. Scattered light from the pattern on the chart 124 is projected onto a portion of the screen of the intensity sensor 211. Light from a second light source not shown is guided by a fiber 111 and projected onto another portion of the screen of the intensity sensor 211. The intensity sensor 211 is driven in the optical axis direction by a stage 212 to acquire multiple defocused images. The defocused image of the chart pattern can be used to calculate the defocus characteristics of the MTF. The transmitted wavefront of the test lens 133 can be calculated using an optimization method from the defocused image of the light emitted from the fiber 111.

[0040] The fiber 111 may be arranged between the chart 124 and the test lens (test optical system) 133. In this case, an absorbing section (black) is arranged upstream of the fiber 111 to prevent light from the scattering section (white) of the chart 124 from overlapping on the intensity sensor 211 near the exit position of the fiber 111. The size D of the absorbing section where the point image is arranged is determined based on the aperture size of the test lens 133 and the defocus amount of the intensity sensor 211 of the light receiving system. More specifically, it is expressed by the following equation (2) using the defocus amount Z of the intensity sensor 211, the numerical aperture Fno of the test lens 133, and the object distance m.

[0041] D=mZ / Fno … (2) Generally, the object distance m is 10 or more. That is, measurement is performed at an object distance m that is 10 times or more the focal length f of the test lens (test optical system) 133. Considering that the maximum value of the defocus amount Z is 0.1Fno to 2Fno [mm], it is preferable that the size D of the absorbing part be at least 1 mm, and preferably 20 mm or more. [Example]

[0042] Next, a method for manufacturing an optical system according to a third embodiment of the present invention will be described with reference to Fig. 8. Fig. 8 is a flowchart of the method for manufacturing an optical system according to this embodiment.

[0043] First, in step S301, a lens is polished to manufacture a single lens (lens manufacturing process). Next, in step S302, single lenses are combined to assemble a lens group (lens assembly process). Alternatively, single lenses or lens groups are combined to assemble an imaging optical system (test optical system). Next, in step S303, the basic aberration of the imaging optical system (test optical system) is measured and evaluated (evaluation process). Next, in step S304, it is determined whether the measured value is better than the standard (OK) or not (NG). If OK, this flow ends. On the other hand, if NG, the imaging optical system (test optical system) is corrected in step S305. After that, the process returns to step S303 again.

[0044] In step S305, the test optical system is corrected by adjusting the adjustment points provided in the test optical system. If the correction cannot be completed by adjusting only the adjustment points, the test optical system is disassembled, and then parts other than the adjustment points are adjusted and reassembled. Alternatively, some lenses in the test optical system are corrected and polished. Alternatively, groups or lenses in defective parts are replaced. By going through the above steps, an optical system with high image quality can be manufactured.

[0045] According to each embodiment, it is possible to provide an optical device, an evaluation device, an evaluation method, and a method for manufacturing an optical system that can easily evaluate the optical performance of various optical systems.

[0046] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0047] 110 laser light source (second light source) 120 Ring light source (first light source) 121, 123, 124 charts 130, 131, 132 Test lens (test optical system) 140, 206, 211 Intensity sensor (light receiving system) 151 SHS (light receiving system) 202 Wavefront sensor (light receiving system) 204 LED light source (first light source)

Claims

1. a first light source and a second light source; a chart that guides light from the first light source to an optical system to be tested; an optical system that forms a point image using light from the second light source; a light receiving system that receives a first light from the chart via the test optical system and a second light from the second light source via the test optical system, the chart has a light-shielding portion and an opening surrounded by the light-shielding portion, the optical system forms the point image at the aperture, the first light and the second light are incident on different positions in the test optical system, 10. An optical device according to claim 9, wherein the size of the point image is smaller than λ / NA, where NA is the numerical aperture of the optical system to be measured and λ is the wavelength of the second light.

2. 2. The optical device according to claim 1, wherein the light receiving system includes a light intensity sensor that receives the first light and a wavefront sensor that receives the second light.

3. 2. The optical device according to claim 1, wherein the light receiving system includes a light intensity sensor that receives the first light and the second light.

4. 4. The optical device according to claim 1, wherein the second light source is a laser light source.

5. 5. The optical device according to claim 1, wherein the first light source has an opening formed therein for transmitting light from the second light source.

6. 6. The optical device according to claim 5, wherein the first light source is a ring light source.

7. 6. The optical device according to claim 5, wherein the first light source is an LED light source configured by arranging a plurality of LEDs.

8. 6. The optical device according to claim 5, wherein the first light source is an illumination light source.

9. 9. An evaluation apparatus comprising: the optical device according to claim 1; and a control unit that evaluates the optical performance of the optical system to be tested using an output from the light receiving system.

10. 10. The evaluation device according to claim 9, wherein the optical performance is a frequency response characteristic at the position of the chart and a wavefront aberration at the position of the point image.

11. A method for manufacturing an optical system having a plurality of lenses, comprising the steps of: manufacturing the plurality of lenses; assembling the optical system with the plurality of lenses; a step of illuminating, using a first light source, a chart on which a plurality of patterns are formed, the chart including an absorbing portion, a transmitting portion, a diffusing plate, a light-shielding portion, and an opening portion surrounded by the light-shielding portion; receiving light emitted from the chart and transmitted through the optical system; calculating a frequency response characteristic of the optical system at the positions of the plurality of patterns based on the light received in the light receiving step; forming a point image at the position of the opening using light from a second light source different from the first light source; receiving light from the second light source that has passed through the optical system with a wavefront sensor; evaluating the optical performance of the optical system by calculating the wavefront aberration of the optical system based on the light received by the wavefront sensor; and adjusting the optical system based on the optical performance.

3. A method for manufacturing an optical system, wherein the step of illuminating the chart and the step of forming the point image are carried out simultaneously.

12. A method for manufacturing an optical system having a plurality of lenses, comprising the steps of: manufacturing the plurality of lenses; assembling the optical system with the plurality of lenses; a step of illuminating, using a first light source, a chart on which a plurality of patterns are formed, the chart including an absorbing portion, a transmitting portion, a diffusing plate, a light-shielding portion, and an opening portion surrounded by the light-shielding portion; receiving light emitted from the chart and transmitted through the optical system; calculating a frequency response characteristic of the optical system at the positions of the plurality of patterns based on the light received in the light receiving step; forming a point image at the position of the opening using light from a second light source different from the first light source; receiving light from the second light source transmitted through the optical system with a light intensity sensor at a plurality of focus positions that are different in an optical axis direction from a focus position of the optical system; evaluating the optical performance of the optical system by calculating wavefront aberration of the optical system based on the plurality of light beams received at the plurality of focus positions; and adjusting the optical system based on the optical performance.

3. A method for manufacturing an optical system, wherein the step of illuminating the chart and the step of forming the point image are carried out simultaneously.

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