Optical system and imaging device having the same

Abstract

To provide an optical system capable of shortening the length in a specific direction. [Solution] The optical system includes a first refractive element through which light from a light source is transmitted, a second refractive element that guides light from the light source to an object, a third refractive element that forms an image of the object, a first reflective element that reflects light from the light source and also reflects light from the object, and a second reflective element that reflects light from the first reflective element. The first refractive element and the third refractive element face each other with the first reflective element in between, and the second refractive element and the second reflective element face each other with the first reflective element in between.

Description

Technical Field

[0001] The present invention relates to an optical system mounted on an imaging device.

Background Art

[0002] Patent Document 1 discloses an imaging device that illuminates an object by epi-illumination.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Disclosure of the Invention

Problems to be Solved by the Invention

[0004] Miniaturization is desired for the optical system as mounted in Patent Document 1.

[0005] An object of the present invention is to provide an optical system capable of shortening the length in a specific direction.

Means for Solving the Problems

[0006] An optical system according to one aspect of the present invention includes a first refractive element through which light from a light source passes, a second refractive element that guides light from the light source to an object, a third refractive element that forms an image of the object, a first reflective element that reflects light from the light source and reflects light from the object, and a second reflective element that reflects light from the first reflective element, wherein the first refractive element and the third refractive element face each other with the first reflective element interposed therebetween, and the second refractive element and the second reflective element face each other with the first reflective element interposed therebetween.

Effects of the Invention

[0007] According to the present invention, it is possible to provide an optical system capable of shortening the length in a specific direction. [Brief explanation of the drawing]

[0008] [Figure 1(a)] This is a schematic cross-sectional view of an example of an imaging device according to an embodiment of the present invention. [Figure 1(b)] This is a schematic cross-sectional view of another example of an imaging device according to an embodiment of the present invention. [Figure 2] This is a schematic cross-sectional view showing the configuration of an imaging device, which is another example of an embodiment of the present invention. [Figure 3(a)] This is a schematic diagram of the main parts of the lighting unit of Example 1. [Figure 3(b)] This is a schematic diagram of the main parts of the imaging unit of Example 1. [Figure 4(a)] This is a schematic diagram of the main parts of the lighting unit in Example 2. [Figure 4(b)] This is a schematic diagram of the main parts of the imaging unit of Example 2. [Figure 5(a)] This is a schematic diagram of the main components of the lighting unit in Example 3. [Figure 5(b)] This is a schematic diagram of the main parts of the imaging unit of Example 3. [Modes for carrying out the invention]

[0009] Embodiments of the present invention will be described in detail below with reference to the drawings. In each drawing, the same reference numeral is used for identical components, and redundant descriptions are omitted.

[0010] In this specification, unless otherwise specified, "lens" may refer to a single lens or a combination of multiple lenses. Furthermore, when "lens" refers to a combination of multiple lenses, at least some of these lenses may constitute a cemented lens or be spaced apart from each other. Additionally, "lens" may include other optical elements such as field diaphragms or diffractive elements.

[0011] Figure 1(a) is a schematic cross-sectional view of imaging device 1001, which is an example of an imaging device according to an embodiment of the present invention, and Figure 1(b) is a schematic cross-sectional view of imaging device 1002, which is another example of an imaging device according to an embodiment of the present invention. In the figures, the solid arrows indicate the illumination optical path (first optical path) for illuminating (irradiating, guiding light) minute objects OBJ such as alignment marks, and the dashed arrows indicate the imaging optical path (second optical path) for imaging the objects OBJ. In the following description, the group of optical elements in the optical path through which the solid arrows pass will be referred to as the illumination unit, and the group of optical elements in the optical path through which the dashed arrows pass will be referred to as the imaging unit. The imaging device of this embodiment is, for example, a microscope that illuminates objects with reflected light illumination.

[0012] The illumination unit includes an illumination lens (first refractive element) IL, a polarizing beam splitter (first reflecting element, reflecting / transmitting element, branching element) PBS, a folding mirror (second reflecting element) M, and an objective lens (second refractive element) OL. The imaging unit includes an objective lens OL, a polarizing beam splitter PBS, and an imaging lens (third refractive element) IO.

[0013] Furthermore, prisms may be used instead of each lens, and perforated mirrors or half-mirrors may be used instead of the polarizing beam splitter PBS.

[0014] Light from the light source SO passes through the illumination lens IL, and its polarization direction is aligned in one direction by the linear polarizer (second polarizer) LP1 so that it is reflected by the polarizing beam splitter PBS, and then incident on the polarizing beam splitter PBS.

[0015] In the configuration of Patent Document 1, the objective lens, beam splitter, lens group, and sensor are arranged along the height direction of the device (the direction perpendicular to the object, the vertical direction), so the dimensions may not be acceptable depending on the device.

[0016] In this embodiment, the illumination lens IL and the imaging lens IO face each other with a polarization beam splitter PBS interposed therebetween, and the objective lens OL and the folding mirror M face each other with a polarization beam splitter PBS interposed therebetween. With such a configuration, it is possible to shorten the length of the imaging device in the height direction and improve the mountability.

[0017] Note that, in this embodiment, each lens is composed only of spherical lenses, but it may be composed in combination with an aspherical lens or a diffractive element.

[0018] The illumination lens IL preferably includes a field stop FS disposed at a position conjugate with the object OBJ and is configured to be able to limit the region for illuminating the object OBJ. By adopting such a configuration, unnecessary illumination outside the observation visual field can be restricted, and stray light can be suppressed.

[0019] The reflecting surface of the polarization beam splitter PBS is composed of, for example, a multilayer film in which a high refractive index material and a low refractive index material are laminated with each other. In FIG. 1(a), the polarization beam splitter PBS is shown with the joining surface of the prism being the multilayer film, but as shown in FIG. 1(b), it may be configured such that the surface of the flat plate is the multilayer film.

[0020] The light incident on the polarization beam splitter PBS is deflected by reflection and folded back toward the object OBJ by the folding mirror M. The folding mirror M preferably has power. It is desirable that the folding mirror M has power because it can increase the design freedom of the objective lens OL and improve the imaging performance and illumination performance. In FIG. 1(a), the folding mirror M is shown as a concave mirror, but a plane mirror or a convex mirror can also be arranged as shown in FIG. 1(b) according to the objective lens OL.

[0021] In this embodiment, when the focal length of the folding mirror is fM and the focal length of the objective lens OL is fOL, it is preferable to satisfy the following conditional expression (1).

[0022] -0.5 ≤ fOL / fM ≤ 0.5 ···(1) If the condition (1) is not met, the power of the folding mirror M becomes too strong, which is undesirable because it can lead to performance degradation due to manufacturing errors and the spacing of optical elements around the polarizing beam splitter PBS becomes too narrow.

[0023] Furthermore, it is preferable that the numerical range of conditional expression (1) be within the range of conditional expression (1a) below.

[0024] -0.4≦fOL / fM≦0.4 (1a) Furthermore, it is more preferable to set the numerical range of condition (1) to the range of condition (1b) below.

[0025] -0.35≦fOL / fM≦0.35 (1b) As mentioned above, since it is desirable for the folding mirror M to have power, in this embodiment it is even more preferable that it satisfies the following condition (2), which is a modified version of condition (1).

[0026] 0.01≦|fOL / fM|≦0.50 ···(2) Furthermore, it is preferable that the numerical range of conditional expression (2) be within the range of conditional expression (2a) below.

[0027] 0.015≦|fOL / fM|≦0.400 ···(2a) Furthermore, it is more preferable to set the numerical range of condition (1) to the range of condition (2b) below.

[0028] 0.02≦|fOL / fM|≦0.35 (2b) A λ / 4 plate (first phase element) PP1 is placed between the polarizing beam splitter PBS and the folding mirror M. Light that has passed through the λ / 4 plate PP1 twice has its polarization direction rotated by 90°, and when it is incident on the polarizing beam splitter PBS again, it is transmitted and illuminates the object OBJ through the objective lens OL. If the telecentricity when illuminating the object OBJ is poor, the image position will change when the object OBJ moves along the optical axis of the objective lens OL. Therefore, it is desirable to improve the telecentricity for applications such as detecting alignment marks.

[0029] Light from the illuminated object OBJ passes again through the objective lens OL and enters the polarizing beam splitter PBS. A λ / 4 plate (second phase element) PP2 is placed between the polarizing beam splitter PBS and the object OBJ. After passing through the λ / 4 plate PP2 twice, the polarization direction of the light is rotated by 90°, and it is reflected and deflected towards the imaging lens IO in the polarizing beam splitter PBS and guided to the image sensor IM. An image of the object OBJ is formed on the imaging surface (light-receiving surface) of the image sensor IM. In other words, the imaging surface of the image sensor IM is positioned at the image plane of the optical system.

[0030] In this embodiment, λ / 4 plates PP1 and PP2 are arranged to rotate the polarization direction by 90°, but other phase elements such as a Faraday rotator may also be arranged.

[0031] The image processing system (processing unit, processor), not shown in the diagram, generates image information based on signals from the image sensor (IM). The generated image is displayed on a screen or the like. The image processing system performs processing according to the application, such as correcting aberrations that could not be corrected by the imaging lens (IO) or combining images taken at different positions into a single image.

[0032] It is desirable to place a linear polarizer (first polarizer) LP2 between the polarizing beam splitter PBS and the image sensor IM. Placing at least one of the linear polarizers LP1 and LP2 is desirable because it can reduce unwanted light (direct light) that has been transmitted from the illumination lens IL to the polarizing beam splitter PBS without being reflected. It is desirable that the direction of polarization transmitted by the linear polarizers LP1 and LP2 be parallel (including approximately parallel), and more preferably perpendicular to the plane containing the illumination light path and the imaging light path (S polarization).

[0033] Furthermore, although Figure 1(a) shows the illumination lens IL and imaging lens IO aligned, the optical axis of the illumination lens IL may be tilted so that their respective optical axes do not coincide (are not parallel to each other), as shown in Figure 1(b). For example, the tilt angle of the optical axis of the illumination lens IL with respect to the optical axis of the imaging lens IO should be between 1 degree and 20 degrees, preferably between 1 degree and 10 degrees, and more preferably between 1 degree and 5 degrees. This suppresses the direct incidence of light from the light source SO onto the center of the image sensor IM.

[0034] Furthermore, as polarizing beam splitters (PBSs) attempt to cover a wider wavelength range, the manufacturing difficulty increases and direct light increases. Therefore, direct light can be reduced by configuring the light source (SO) to emit light with a full width at half maximum of 100 nanometers or less.

[0035] As explained above, in imaging devices 1001 and 1002, light from the light source SO passes through the polarizing beam splitter PBS, then through the illumination lens IL, the folding mirror M, the objective lens OL, and the imaging lens IO in that order, before entering the image sensor IM.

[0036] In this configuration, the objective lens OL, the polarizing beam splitter PBS, and the folding mirror M are arranged along a direction perpendicular to the object OBJ, while the illumination lens IL and imaging lens IO, which increase the overall optical length, are placed to the left and right of the polarizing beam splitter PBS. This reduces the height dimension relative to the object OBJ, making it possible to realize an optical system that is easy to mount.

[0037] The following describes the imaging device 1003, which has a different configuration from the imaging devices 1001 and 1002 in Figure 1, with reference to Figure 2. Figure 2 is a schematic cross-sectional view showing the configuration of the imaging device 1003.

[0038] The illumination unit includes an illumination lens IL, a polarizing beam splitter PBS, and an objective lens OL. The imaging unit includes an objective lens OL, a polarizing beam splitter PBS, a folding mirror M, and an imaging lens IO.

[0039] Light from the light source SO passes through the polarizing beam splitter PBS, then through the illumination lens IL, objective lens OL, folding mirror M, and imaging lens IO in that order, before entering the image sensor IM.

[0040] In imaging devices 1001 and 1002, light from the illuminated object OBJ passes through the objective lens OL, polarizing beam splitter PBS, and imaging lens IO in that order before being guided to the image sensor IM. In imaging device 1003, light from the illuminated object OBJ passes through the objective lens, polarizing beam splitter, folding mirror, polarizing beam splitter, and imaging lens in that order, resulting in a larger number of optical elements contributing to imaging performance compared to imaging devices 1001 and 1002. In particular, the increased number of folding mirrors M may improve design performance, but it may also increase the possibility of performance degradation due to manufacturing errors, so it is desirable to select the configuration according to the specifications of the imaging device. [Examples]

[0041] The illumination unit and imaging unit of the optical system in this embodiment will be described in detail below with reference to Figures 3(a), 3(b), and Tables 1 and 2.

[0042] Figures 3(a) and 3(b) are schematic diagrams of the main components of the illumination unit and imaging unit, respectively. Tables 1 and 2 show numerical examples corresponding to this embodiment. Specifically, they show the radius of curvature r [mm] of the optical surface of the light source SO, object OBJ, image sensor IM, and each optical element, and the on-axial spacing (distance along the optical axis) spacing d [mm] between the m-th and (m+1)-th surfaces in the illumination unit and imaging unit of this embodiment. Nd and νd represent the refractive index and Abbe number for a wavelength of 587.6 nm, respectively.

[0043] The configurations of the illumination unit and imaging unit in this embodiment are the same as those of the illumination unit and imaging unit in imaging devices 1001 and 1002, respectively, and the illumination unit includes a folding mirror M. The illumination lens IL is composed of three lenses and a field aperture FS, the objective lens OL is composed of five lenses, and the imaging lens IO is composed of two lenses. In this embodiment, the folding mirror M has a concave shape, and the telecentricity with respect to the object OBJ is kept below 20 mrad. The numerical aperture NA on the object side of the imaging unit is 0.2, and the magnification is 5x. It is configured telecentrically with respect to the object OBJ, and the worst wavefront aberration value for white light is kept below 40 mλrms.

[0044] Various data fOL=4.3 fM=13.1 fOL / fM = 0.33 (Table 1) (Lighting unit) JPEG2026106681000002.jpg217105

[0045] (Table 2) (Imaging unit) JPEG2026106681000003.jpg220119 [Examples]

[0046] The illumination unit and imaging unit of the optical system in this embodiment will be described in detail below with reference to Figures 4(a), 4(b), and Tables 3 and 4.

[0047] Figures 4(a) and 4(b) are schematic diagrams of the main components of the illumination unit and imaging unit, respectively. Tables 3 and 4 show numerical examples corresponding to this embodiment. Specifically, they show the radius of curvature r [mm] of the optical surface of the light source SO, object OBJ, image sensor IM, and each optical element, and the on-axial spacing (distance along the optical axis) spacing d [mm] between the m-th plane and the (m+1)-th plane in the illumination unit and imaging unit of this embodiment. Nd and νd represent the refractive index and Abbe number for a wavelength of 587.6 nm, respectively.

[0048] The configurations of the illumination unit and imaging unit in this embodiment are the same as those of the illumination unit and imaging unit in imaging devices 1001 and 1002, respectively, and the illumination unit includes a folding mirror M. The illumination lens IL is composed of three lenses and a field aperture FS, the objective lens OL is composed of six lenses, and the imaging lens IO is composed of four lenses. In this embodiment, the folding mirror M has a convex shape, and the telecentricity with respect to the object OBJ is kept below 10 mrad. The numerical aperture NA on the object side of the imaging unit is 0.2, and the magnification is 5x. It is configured telecentrically with respect to the object OBJ, and the worst wavefront aberration value for white light is kept below 30 mλrms.

[0049] Various data fOL=4.1 fM = -37.5 fOL / fM = -0.11 (Table 3) (Lighting unit) JPEG2026106681000004.jpg22989

[0050] (Table 4) (Imaging unit) JPEG2026106681000005.jpg226102 [Examples]

[0051] The illumination unit and imaging unit of the optical system in this embodiment will be described in detail below with reference to Figures 5(a), 5(b), and Tables 5 and 6.

[0052] Figures 5(a) and 5(b) are schematic diagrams of the main components of the illumination unit and imaging unit, respectively. Tables 5 and 6 show numerical examples corresponding to this embodiment. Specifically, they show the radius of curvature r [mm] of the optical surface of the light source SO, object OBJ, image sensor IM, and each optical element, and the on-axial spacing (distance along the optical axis) spacing d [mm] between the m-th plane and the (m+1)-th plane in the illumination unit and imaging unit of this embodiment. Nd and νd represent the refractive index and Abbe number for a wavelength of 587.6 nm, respectively.

[0053] The configurations of the illumination unit and imaging unit in this embodiment are the same as those of the illumination unit and imaging unit of the imaging device 1003, respectively, with the imaging unit including a folding mirror M. The illumination lens IL is composed of three lenses and a field aperture FS, the objective lens OL is composed of six lenses, and the imaging lens IO is composed of two lenses. In this embodiment, the folding mirror M has a convex shape, and the telecentricity with respect to the object OBJ is kept below 10 mrad. The numerical aperture NA on the object side of the imaging unit is 0.2, and the magnification is 5x. It is configured telecentrically with respect to the object OBJ, and the worst wavefront aberration value for white light is kept below 30 mλrms.

[0054] Various data fOL=3.9 fM=23.0 fOL / fM = -0.03 (Table 5) (Lighting unit) JPEG2026106681000006.jpg222109

[0055] (Table 6) (Imaging unit) JPEG2026106681000007.jpg225100

[0056] This embodiment includes the following configuration. (Composition 1) A first refractive element through which light from a light source passes, A second refractive element that guides light from the aforementioned light source to an object, A third refractive element that forms an image of the object, A first reflective element that reflects light from the light source and also reflects light from the object, It comprises a second reflective element that reflects light from the first reflective element, The first refractive element and the third refractive element face each other with the first reflective element in between. An optical system characterized in that the second refractive element and the second reflective element face each other with the first reflective element in between. (Configuration 2) The optical system according to configuration 1, characterized in that the second reflective element has power. (Composition 3) When the focal length of the second reflecting element is fM and the focal length of the second refractive element is fOL, -0.5 ≤ fOL / fM ≤ 0.5 The optical system according to configuration 1 or 2, characterized by satisfying the following conditional expression. (Composition 4) When the focal length of the second reflecting element is fM and the focal length of the second refractive element is fOL, 0.01 ≤ |fOL / fM| ≤ 0.50 An optical system according to any one of configurations 1 to 3, characterized by satisfying the following conditional expression. (Composition 5) The optical system according to any one of configurations 1 to 4, further comprising a first polarizer disposed between the first reflecting element and the image plane. (Composition 6) The optical system according to any one of configurations 1 to 5, further comprising a second polarizer disposed between the first reflective element and the light source. (Composition 7) A first polarizer is disposed between the first reflecting element and the image plane, The system further comprises a second polarizer disposed between the first reflective element and the light source, The optical system according to any one of configurations 1 to 6, characterized in that the directions of polarization transmitted by the first and second polarizers are parallel. (Composition 8) It has a first optical path for guiding light from the light source to the object and a second optical path for guiding light from the object to the image plane. The optical system according to configuration 7, characterized in that the direction of polarization transmitted by the first and second polarizers is perpendicular to the plane containing the first and second optical paths. (Composition 9) The optical system according to any one of configurations 1 to 8, characterized in that the optical axis of the first refractive element and the optical axis of the third refractive element are nonparallel to each other. (Composition 10) Light from the light source passes through the first refractive element, is reflected by the first reflective element, is reflected by the second reflective element, passes through the second refractive element, and illuminates the object. The optical system according to any one of configurations 1 to 9, characterized in that light from the object passes through the second refractive element, is reflected by the first reflective element, passes through the third refractive element, and is incident on the image plane. (Composition 11) The first reflecting element is a beam splitter, Light from the light source passes through the first refractive element, is reflected by the beam splitter, is reflected by the second reflecting element, passes through the beam splitter, passes through the second refractive element, and illuminates the object. The optical system according to configuration 10, characterized in that light from the object passes through the second refractive element, is reflected by the beam splitter, passes through the third refractive element, and is incident on the image plane. (Composition 12) Light from the light source passes through the first refractive element, is reflected by the first reflecting element, passes through the second refractive element, and illuminates the object. The optical system according to any one of configurations 1 to 9, characterized in that light from the object passes through the second refractive element, is reflected by the second reflective element, is reflected by the first reflective element, passes through the third refractive element, and enters the image plane. (Composition 13) The first reflecting element is a beam splitter, Light from the light source passes through the first refractive element, is reflected by the beam splitter, passes through the second refractive element, and illuminates the object. The optical system according to claim 12, characterized in that light from the object passes through the second refractive element, passes through the beam splitter, is reflected by the second reflecting element, is reflected by the beam splitter, passes through the third refractive element, and is incident on the image plane. (Composition 14) A first phase element is positioned between the first reflecting element and the second reflecting element, The optical system according to any one of configurations 1 to 13, further comprising a second phase element disposed between the first reflecting element and the second refractive element. (Composition 15) An imaging device characterized by having an optical system described in any one of configurations 1 to 14, and an image sensor that receives an image of the object. (Composition 16) The imaging apparatus according to configuration 15, wherein the light source emits light with a half-width of 100 nanometers or less.

[0057] Although 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 its gist. [Explanation of symbols]

[0058] SO light source IL illumination lens (first refractive element) PBS polarizing beam splitter (first reflecting element) M Folding mirror (second reflecting element) OL objective lens (second refractive element) OBJ object IO imaging lens (third refractive element)

Claims

1. A first refractive element through which light from a light source passes, A second refractive element that guides light from the aforementioned light source to an object, A third refractive element that forms an image of the object, A first reflective element that reflects light from the light source and also reflects light from the object, It comprises a second reflective element that reflects light from the first reflective element, The first refractive element and the third refractive element face each other with the first reflective element in between. An optical system characterized in that the second refractive element and the second reflective element face each other with the first reflective element in between.

2. The optical system according to claim 1, characterized in that the second reflective element has power.

3. When the focal length of the second reflecting element is fM and the focal length of the second refractive element is fOL, -0.5 ≤ fOL / fM ≤ 0.5 The optical system according to claim 1 or 2, characterized in that it satisfies the following conditional expression.

4. When the focal length of the second reflecting element is fM and the focal length of the second refractive element is fOL, 0.01≦|fOL / fM|≦0.50 The optical system according to claim 1 or 2, characterized in that it satisfies the following conditional expression.

5. The optical system according to claim 1 or 2, further comprising a first polarizer disposed between the first reflective element and the image plane.

6. The optical system according to claim 1 or 2, further comprising a second polarizer disposed between the first reflective element and the light source.

7. A first polarizer is disposed between the first reflecting element and the image plane, The system further comprises a second polarizer disposed between the first reflective element and the light source, The optical system according to claim 1 or 2, characterized in that the directions of polarization transmitted by the first and second polarizers are parallel.

8. It has a first optical path for guiding light from the light source to the object and a second optical path for guiding light from the object to the image plane. The optical system according to claim 7, characterized in that the direction of polarization transmitted by the first and second polarizers is perpendicular to the plane containing the first and second optical paths.

9. The optical system according to claim 1 or 2, characterized in that the optical axis of the first refractive element and the optical axis of the third refractive element are non-parallel to each other.

10. Light from the light source passes through the first refractive element, is reflected by the first reflective element, is reflected by the second reflective element, passes through the second refractive element, and illuminates the object. The optical system according to claim 1 or 2, characterized in that light from the object passes through the second refractive element, is reflected by the first reflective element, passes through the third refractive element, and enters the image plane.

11. The first reflecting element is a beam splitter, Light from the light source passes through the first refractive element, is reflected by the beam splitter, is reflected by the second reflecting element, passes through the beam splitter, passes through the second refractive element, and illuminates the object. The optical system according to claim 10, characterized in that light from the object passes through the second refractive element, is reflected by the beam splitter, passes through the third refractive element, and is incident on the image plane.

12. Light from the light source passes through the first refractive element, is reflected by the first reflecting element, passes through the second refractive element, and illuminates the object. The optical system according to claim 1 or 2, characterized in that light from the object passes through the second refractive element, is reflected by the second reflective element, is reflected by the first reflective element, passes through the third refractive element, and enters the image plane.

13. The first reflecting element is a beam splitter, Light from the light source passes through the first refractive element, is reflected by the beam splitter, passes through the second refractive element, and illuminates the object. The optical system according to claim 12, characterized in that light from the object passes through the second refractive element, passes through the beam splitter, is reflected by the second reflecting element, is reflected by the beam splitter, passes through the third refractive element, and is incident on the image plane.

14. A first phase element disposed between the first reflecting element and the second reflecting element, The optical system according to claim 1 or 2, further comprising a second phase element disposed between the first reflecting element and the second refractive element.

15. An imaging device characterized by having an optical system according to claim 1 or 2 and an image sensor that receives an image of the object.

16. The imaging apparatus according to claim 15, wherein the light source emits light with a half-width of 100 nanometers or less.

Images