Optical system and imaging device

Abstract

It provides a good optical system as a polarized reflection imaging system. [Solution] The optical system has a first transmission reflective surface, a first phase shifter, a second transmission reflective surface, and a second phase shifter. When Rh1 is the radius of curvature of the first transmission reflective surface on the optical axis, Rr1 is the radius of curvature of the surface on the optical axis where the first phase shifter is provided, Rr2 is the radius of curvature of the surface on the optical axis where the second phase shifter is provided, f is the focal length of the optical system, FNo is the F number, and Y is the maximum image height, the following conditions are satisfied: |Y / Rh1|≦0.20, |Y / Rr1|≦0.20, |Y / Rr2|≦0.20, and 0.30≦(FNo×Y) / f≦1.75.

Description

[Technical Field]

[0001] The present invention relates to an optical system suitable for imaging. [Background Art]

[0002] Patent Documents 1 and 2 disclose methods for manufacturing an optical system used in an objective optical system for an endoscope, an imaging optical system for an HMD (head-mounted display), or the like by using a technology called wafer level optics.

[0003] Further, as a compact optical system, a polarization reflection imaging system combining a polarizing element and a half mirror as disclosed in Patent Document 3 is used. [Prior Art Documents] [Patent Documents]

[0004] [Patent Document 1] U.S. Pat. No. 9,798,115 [Patent Document 2] Japanese Unexamined Patent Application Publication No. 2011-081315 [Patent Document 3] Japanese Unexamined Patent Application Publication No. 2005-352273 [Summary of the Invention] [Problem to be Solved by the Invention]

[0005] There is a demand for an optical system using a polarizing element that has better performance than conventional optical systems. [Means for Solving the Problem]

[0006] An optical system according to one aspect of the present invention is an optical system including a first transmission-reflection surface, a first phase shifter, a second transmission-reflection surface, and a second phase shifter that are arranged in order, wherein when Rh1 is the radius of curvature of the first transmission-reflection surface on the optical axis, Rr1 is the radius of curvature of the surface provided with the first phase shifter on the optical axis, Rr2 is the radius of curvature of the surface provided with the second phase shifter on the optical axis, f is the focal length of the optical system, FNo is the F-number, and Y is the maximum image height, |Y / Rh1|≦0.20 |Y / Rr1|≦0.20 |Y / Rr2|≦0.20 0.30 ≤ (FNo × Y) / f ≤ 1.75 It is characterized by satisfying the following conditions. Furthermore, an imaging device equipped with the above optical system also constitutes another aspect of the present invention. [Effects of the Invention]

[0007] According to the present invention, a good optical system can be provided as an optical system using a polarizing element. [Brief explanation of the drawing]

[0008] [Figure 1] Cross-sectional view of the optical system of Example 1. [Figure 2] Aberration diagram of the optical system in Example 1. [Figure 3] Cross-sectional view of the optical system in Example 2. [Figure 4] Aberration diagram of the optical system in Example 2. [Figure 5] Cross-sectional view of the optical system of Example 3. [Figure 6] Aberration diagram of the optical system in Example 3. [Figure 7] Cross-sectional view of the optical system of Example 4. [Figure 8] Aberration diagram of the optical system in Example 4. [Figure 9] Cross-sectional view of the optical system of Example 5. [Figure 10] Aberration diagram of the optical system in Example 5. [Figure 11] Cross-sectional view of the optical system of Example 6. [Figure 12] Aberration diagram of the optical system in Example 6. [Figure 13] Cross-sectional view of the optical system of Example 7. [Figure 14] Aberration diagram of the optical system in Example 7. [Figure 15] Cross-sectional view of the optical system of Example 8. [Figure 16] Aberration diagram of the optical system in Example 8. [Figure 17]Schematic diagram showing the optical path of an optical system. [Figure 18] Schematic diagram showing the optical path of another optical system. [Figure 19] Schematic diagram of an image pickup apparatus provided with the optical systems of Examples 1 to 8. [Figure 20] Schematic diagram of another image pickup apparatus provided with the optical systems of Examples 1 to 8. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0010] The optical system of each embodiment is an optical system obtained by using wafer level optics. Wafer level optics is a wafer process for manufacturing a large number of optical systems at one time by forming a large number of lenses on a wafer using semiconductor manufacturing technology, overlapping and bonding a plurality of wafers (flat substrates), and then cutting the stacked wafers. An optical system manufactured by using wafer level optics is called a wafer level lens, and an image pickup apparatus using the wafer level lens as an imaging optical system is called a wafer level camera.

[0011] The optical system of each embodiment is used together with display optical systems such as viewfinders and HMDs, and is used in optical systems for line-of-sight detection, external environment imaging, and the like. It is also used for objective optical systems for endoscopes and cameras incorporated in electronic devices such as mobile phones, smartphones, and wearable terminals.

[0012] Figures 1, 3, 5, 7, 9, 11, 13 and 15 show cross-sections of the optical systems (wafer level lenses) of Examples 1 to 8. In each cross-sectional view, the left side is the object side (front side) and the right side is the image side (rear side). SP is an aperture stop, and IP is an image plane. On the image plane IP, there is disposed an imaging surface of an image pickup element (image sensor) such as a CCD sensor or a CMOS sensor in an image pickup apparatus, or a photosensitive surface corresponding to the film surface of a silver halide film camera. OA is the optical axis of the optical system. The direction in which the optical axis OA extends is referred to as the optical axis direction.

[0013] The optical system of each embodiment includes an aperture diaphragm SP and a first transmission reflective surface HM1, a first phase shifter RT1, a second transmission reflective surface HM2, and a second phase shifter RT2 arranged in order in the optical axis direction. The optical system of each embodiment also includes a first lens unit L1, a second lens unit L2, and a third lens unit L3, or a first lens unit L1 and a second lens unit L2, arranged in order from the object side to the image side. The aperture diaphragm SP, the first transmission reflective surface HM1, the first phase shifter RT1, the second transmission reflective surface HM2, and the second phase shifter RT2 are provided in one of the first to third lens units L1 to L3.

[0014] The optical system in each embodiment does not have a lens unit that moves for focusing.

[0015] Although the optical system in each embodiment has three or two lens units, it may have four or more units. Furthermore, cover glasses such as parallel plates may be placed closer to the object than the lens unit closest to the object, and closer to the image than the lens unit closest to the image.

[0016] The first to third lens units L1 to L3 are manufactured using a wafer process. Specifically, they are manufactured by forming a lens layer made of a curable resin material on a wafer made of glass material, or by pouring a curable resin between two opposing molds to form a wafer in which the substrate and lens are integrally molded. A large number of wafer-level lenses can be manufactured by arranging the lens unit and the cover glass of the image sensor with a gap between them, bonding them outside the effective region through which the light rays contributing to imaging pass, and then cutting them. The material used to form the lens layer can be any curable resin material, such as a thermoplastic resin or an ultraviolet-curable resin. Examples include acrylic resin, silicone resin, and cycloolefin polymer.

[0017] The aperture diaphragm SP can be formed, for example, by depositing a light-shielding film such as chromium using a mask, or by etching the opening after deposition. In this case, forming the aperture diaphragm SP on a flat surface such as a substrate is preferable from a manufacturing standpoint because it facilitates control of the mask placement in the thickness direction.

[0018] In one embodiment of the optical system, light incident from the object side passes through the first transmission reflective surface HM1 and the first phase shifter RT1 in sequence, and is reflected by the second transmission reflective surface HM. The light then passes through the first phase shifter RT1 and is reflected by the first transmission reflective surface HM1, and passes through the first phase shifter RT1, the second transmission reflective surface HM2, and the second phase shifter RT2 in that order to reach the image plane IP.

[0019] In another embodiment of the optical system, light incident from the object side passes through the second phase shifter RT2, the second transmission reflective surface HM2, and the first phase shifter RT1 in that order, and is reflected by the second transmission reflective surface HM2. The light then passes through the first phase shifter RT1, is reflected by the second transmission reflective surface HM2, and passes through the first phase shifter RT1 and the first transmission reflective surface HM1 in that order to reach the image plane IP.

[0020] The first and second transmissive reflective surfaces HM1 and HM2 do not necessarily have to have a transmittance of 50% and a reflectance of 50%. The ratio of transmittance to reflectance for randomly polarized light is preferably in the range of 1:3 to 3:1. Randomly polarized light is defined as light with Stokes parameters S0=1 and S1=S2=S3=0. Furthermore, the first and second transmissive reflective surfaces HM1 and HM2 may also have absorptive properties. Lenses may also be formed or bonded to one or both sides of each transmissive reflective surface.

[0021] As phase shifters, Faraday rotators and quarter-wave plates (λ / 4 plates) such as QWPs can be used. In each embodiment, a QWP is used as the phase shifter. As a QWP, for example, a birefringent polymer film or a liquid crystal alignment layer can be used. Laminates of such polymer films or liquid crystal alignment layers can also be used. By properly laminating, a phase difference close to one-quarter of the wavelength can be obtained over a wide wavelength range. For example, "WA-140T" from Nippon Kayaku Co., Ltd. and "PolarCorrect" from ColorLink Japan Co., Ltd. can be used. In addition to the above, inorganic wave plates from Dexerials, Inc. can also be used as QWPs.

[0022] Furthermore, the QWP may be bonded to the first transmission reflective surface HM1 or the second transmission reflective surface HM2, or it may be bonded separately from these transmission reflective surfaces. The QWP may also be inserted into the optical path as a film, or a film bonded to a glass plate may be inserted into the optical path. Lenses may also be formed or bonded to one or both sides of the QWP. For example, lenses can be formed on one or both sides of an inorganic waveplate using wafer-level optics with the inorganic waveplate as the substrate.

[0023] The characteristics of the optical systems in each embodiment will be described below. As mentioned above, the optical systems in each embodiment are wafer-level optics, and miniaturization is important for their applications. It is also necessary to reduce the number of wafers to lower costs. For this reason, the optical systems in each embodiment use a polarized reflection imaging system.

[0024] [Polarization Utilization Configuration 1] Figure 17 shows the use of polarization in an optical system composed of a polarization-selective transmission reflective element PBS:A as the first transmission reflective surface, a first λ / 4 plate QWP1:B, a half mirror HM:C as the second transmission reflective surface, a second λ / 4 plate QWP2:D, and a linear polarizer POL:E, arranged in order from the object side (left side of the figure) to the image (imaging plane IM) side.

[0025] A PBS is configured to reflect linearly polarized light with the same polarization direction as the linearly polarized light transmitted through a linear polarizer POL, and to transmit linearly polarized light with a polarization direction perpendicular to it. A PBS is a wire grid polarizer or a phase difference film laminated type reflective polarizer. The wire grid forming surface or phase difference film surface of the PBS functions as a transmitting and reflecting surface. Note that a wire grid polarizer does not necessarily have to be made of aligned metal wires; it can be any element that has thin metal or dielectric layers arranged at predetermined intervals and functions as a transmitting and reflecting element. For example, an element in which layers of metal or dielectric are aligned by vapor deposition can be used.

[0026] QWP1 and QWP2 are positioned so that their slow axes are tilted at 45° with respect to the transmission axis of the POL. Preferably, QWP1 and QWP2 are positioned so that their respective slow axes are tilted at 90°. With this arrangement, the wavelength dispersion characteristics of the waveplates cancel each other out when light rays pass through QWP1 and QWP2.

[0027] HM is a half-mirror formed, for example, by dielectric multilayer film or metal deposition, and functions as a transmissive reflective surface. POL is, for example, an absorbing linear polarizer.

[0028] Of the light incident on the optical system from the object side, linearly polarized light that passes through PBS is converted to circularly polarized light by QWP1. This circularly polarized light is incident on HM, and a portion of it is reflected back to QWP1 as reverse-polarized light. The reverse-polarized light that returns to QWP1 is converted by QWP1 to linearly polarized light with a polarization direction perpendicular to the polarization direction of the linearly polarized light that previously passed through PBS, and this linearly polarized light returns to PBS and is reflected.

[0029] On the other hand, the circularly polarized light transmitted through HM is converted by QWP2 to linearly polarized light with the same polarization direction as the linearly polarized light that previously transmitted through PBS, and is then absorbed by POL.

[0030] The linearly polarized light reflected by PBS is converted to circularly polarized light by QWP1, and this circularly polarized light is incident on HM. A portion of the circularly polarized light incident on HM passes through it and is incident on QWP2, where it is converted to linearly polarized light with the same polarization direction as the linearly polarized light reflected by PBS. The linearly polarized light emitted from QWP2 is incident on POL. Since the polarization direction of the incident linearly polarized light matches the orientation of the transmission axis of POL, most of it passes through POL and reaches IM.

[0031] With the polarization-utilizing configuration described above, only the light that passes through PBS, is reflected by HM, is reflected again by PBS, and then passes through HM again reaches IM.

[0032] Furthermore, when using a cholesteric liquid crystal instead of HM as the second transmission reflective surface, it is preferable to position the cholesteric liquid crystal so that it reflects a large amount of incident circularly polarized light during its first reflection. This makes it possible to increase the amount of light in the normal optical path while reducing ghost light.

[0033] Furthermore, image sensors such as CCD sensors and CMOS sensors generally have a high reflectivity of the imaging surface. Therefore, the light reflected by the IM passes through the POL again and is converted to circular polarization by the QWP2. Subsequently, this circular polarization is reflected by the HM to become reverse-polarized light and enters the QWP2 again. This reverse-polarized light is converted by the QWP2 to linear polarization with a polarization direction perpendicular to the polarization direction of the linear polarization that passed through the POL immediately before, and this linear polarization enters the POL. Since the polarization direction of this linear polarization is perpendicular to the direction of the transmission axis of the POL, most of it is absorbed by the POL.

[0034] In this way, since most of the light reflected by the IM and HM is cut off, ghosting and flare become less noticeable. It is preferable that, in order to achieve this reflection reduction effect, there is no optical low-pass filter utilizing birefringence between the IM and POL. This is because an optical low-pass filter causes the polarization state to deviate from linear polarization.

[0035] Furthermore, in this configuration, a quarter-wave plate may be placed between the polarization-selective transmission / reflection element A and the object. In this case, the quarter-wave plate is positioned so that the angle between its leading or lagging axis and the transmission axis of the polarization-selective transmission / reflection element A is 45°. By doing so, a pseudo-depolarization is performed, making it possible to image even if the light incident from the object side is linearly polarized, regardless of its polarization direction. Alternatively, a depolarization element may be placed instead of the quarter-wave plate. For example, Toyobo Co., Ltd.'s "CosmoShine SRF" can be used as a depolarization element. CosmoShine SRF is a film with a large birefringence of around 10,000 nm, and by using such a film, it may be possible to prevent color unevenness caused by the wavelength and angular characteristics of the wave plate compared to when a quarter-wave plate is used.

[0036] In this configuration, a λ / 4 plate may be placed between the PBS and the object. In this case, the λ / 4 plate is positioned so that its leading or lagging axis is at a 45° angle to the transmission axis of the PBS. This effectively eliminates polarization, making it possible to image even if the light incident from the object is linearly polarized, regardless of its polarization direction. Alternatively, a depolarization element may be placed instead of the λ / 4 plate. As a depolarization element, "CosmoShine SRF" manufactured by Toyobo Co., Ltd. can be used. CosmoShine SRF is a film with a large birefringence of around 10,000 nm, and it is expected that using such a film can prevent color unevenness caused by the wavelength and angular characteristics of the λ / 4 plate.

[0037] [Polarization Utilization Configuration 2] Figure 18 shows the use of polarization in an optical system composed of a first linear polarizer POL1:E, a second λ / 4 plate QWP2:D, a half mirror HM:C as a second transmission / reflection surface, a first λ / 4 plate QWP1:B, and a polarization-selective transmission / reflection element PBS:A as a first transmission / reflection surface, arranged in order from the object side to the image (imaging surface IM) side. The configuration of the polarization-selective transmission / reflection element, λ / 4 plate, and linear polarizer, as well as the orientation of the optical axis, are the same as in polarization utilization configuration 1.

[0038] Of the light incident on the optical system from the object side, the linearly polarized light that passes through POL1 is converted to circularly polarized light by QWP2. This circularly polarized light is incident on HM, and a portion of it is reflected back to QWP2 as reverse-polarized light. The reverse-polarized light that has returned to QWP2 is converted by QWP2 into linearly polarized light with a polarization direction perpendicular to the polarization direction of the linearly polarized light that previously passed through POL1, and this linearly polarized light is absorbed by POL1.

[0039] Meanwhile, the circularly polarized light transmitted through HM is converted by QWP1 into linearly polarized light with the same polarization direction as the linearly polarized light that previously transmitted through POL, and then incident on PBS. This linearly polarized light is reflected by PBS and returns to QWP1. The linearly polarized light that returns to QWP1 is converted into circularly polarized light, and a portion of this circularly polarized light is reflected by HM to become reverse-polarized light, which then incident on QWP1 again. The reverse-polarized circularly polarized light incident on QWP1 is converted into linearly polarized light with a polarization direction perpendicular to the polarization direction of the linearly polarized light previously reflected by PBS. This linearly polarized light passes through PBS and reaches IM.

[0040] With the polarization-utilizing configuration described above, only the light that passes through HM, is reflected by PBS, is reflected by HM again, and passes through PBS again reaches IM.

[0041] In this configuration, a second linear polarizer POL2:A′ may be placed between PBS and IM. In this case, the orientation of the transmission axes of POL2 and PBS should be aligned. This allows for the absorption of light that would otherwise be reflected by IM, reflected by PBS, and then incident back into IM, resulting in ghosting or flare.

[0042] In this configuration, a λ / 4 plate may be placed between POL1 and the object. In this case, the λ / 4 plate is positioned so that its leading or lagging axis forms a 45° angle with respect to the transmission axis of POL1. This makes it possible to perform imaging regardless of the polarization direction, even if the light incident from the object side is linearly polarized. Alternatively, a depolarization element as described in Polarization Utilization Configuration 1 may be placed instead of the λ / 4 plate.

[0043] In the above explanations of the two polarization utilization configurations, we used orthogonal, the same (parallel), and 45° angles. However, these do not strictly represent 90°, 0°, and 45°, but rather any angle within ±5° of these angles is acceptable, and within ±2°, and even more preferably within ±1°.

[0044] In the two polarization-utilizing configurations described above, it is desirable to use the same λ / 4 plate as QWP1 and QWP2. However, different λ / 4 plates may be used as long as they are ideal (i.e., they give exactly a 1 / 4 wavelength phase to all usable wavelengths and angles of incidence of the light rays). In the two polarization-utilizing configurations described above, the phases given by QWP1 and QWP2 as light passes through them are precisely canceled out, so that only specific rays are emitted towards the image side. That is, light reflected once each by PBS and HM is emitted towards the image side, and light that has not been reflected at all or light that has been reflected twice each is absorbed by the linear polarizer. In this case, if the characteristics of QWP1 and QWP2 are different, unintended light will be emitted towards the image side, resulting in larger ghosting and flares.

[0045] Furthermore, in the two polarization utilization configurations described above, an image sensor including an optical low-pass filter may be used. In this case, it is preferable that the relative angle between the transmission axis of the linear polarizer on the image side and the phase-advancing axis of the birefringent plate on the object side among the birefringent plates constituting the optical low-pass filter be 45° or 135°. This makes it possible to obtain a low-pass effect similar to that of a normal optical system, which has almost no polarization dependence, like a general refractive optical system. Alternatively, a λ / 4 plate may be placed on the image side of the polarizer on the image side. In this case, it is preferable that the relative angle between the phase-advancing axis of the λ / 4 plate and the transmission axis of the linear polarizer on the image side be 45° or 135°. This makes it possible to obtain a low-pass effect similar to that of a normal optical system by emitting circularly polarized light toward the image sensor. Furthermore, by placing a plastic molded lens with large birefringence on the image side of the linear polarizer on the image side, the emitted light may be made into pseudo-random polarization, thereby making a low-pass effect similar to that of a normal optical system.

[0046] Furthermore, in the two polarization utilization configurations described above, the polarization-selective transmission / reflection element, λ / 4 plate, and linear polarizer may be circular or rectangular. When using film-like materials, mainly polymer materials, as these polarizing elements, it is preferable to laminate them to a glass plate or resin plate, as mentioned above, to ensure sufficient surface accuracy. By laminating a large film to a glass plate or resin plate and then cutting out rectangles or other shapes from it, material loss can be reduced. In the two polarization utilization configurations described above, the azimuth relationship between the polarizing elements is important, as mentioned above. By using rectangular polarizing elements, it becomes easier to guarantee the external shape of the components and the orientation of the elements (leading axis / lagging axis, transmission axis / absorption axis, transmission axis / reflection axis) on a component-by-component basis, and azimuth adjustment can be simplified or even omitted.

[0047] Next, the preferred configurations and conditions that the optical systems of each embodiment satisfy will be described. In order to construct a polarization-reflective imaging system using wafer-level optics, as mentioned above, it is necessary to arrange a polarization-selective transmission-reflective element, a phase shifter, a half-mirror, and a phase shifter in the order described above in the optical axis direction. It is preferable to use a wire grid polarizer or a phase difference film stacked element as the polarization-selective transmission-reflective element. Forming wire grid polarizers or phase difference film stacked elements on a surface with high curvature is difficult to manufacture. In particular, in wafer processes, since multiple optical surfaces are arranged on a single wafer, if the curvature of the optical surface is large, it will result in a minute uneven structure within the wafer surface. In this case, the molding stability deteriorates when bonding films or forming wire grid structures.

[0048] Similarly, it is preferable to use a λ / 4 wave plate for the phase shifter. In this case, even with a λ / 4 wave plate, a process of bonding a film-like element to the optical surface of the substrate is preferable in terms of ease of manufacturing, but if the curvature of the optical surface is large, the manufacturing stability deteriorates.

[0049] On the other hand, for the transmissive reflective surface where the half-mirror is formed, multilayer films made by depositing inorganic dielectrics or films made by depositing metal-absorbing materials are used. These deposition processes are also applicable to wafer-level optics, and film formation is possible even if the curvature of the optical surface is large.

[0050] Based on these considerations, it is preferable that the optical system of each embodiment satisfies the following equations (1) to (3), where Rh1 is the radius of curvature of the first transmission / reflection surface on the optical axis, Rr1 is the radius of curvature of the surface on which the first phase shifter is formed on the optical axis, Rr2 is the radius of curvature of the surface on which the second phase shifter is formed on the optical axis, and Y is the maximum image height of the optical system. The maximum image height is the maximum height from the optical axis of the image position on the image plane (evaluation surface), and corresponds to the radius of the image circle formed by the optical system. The first transmission / reflection surface may be aspherical, but it is preferable that it be spherical or planar considering ease of manufacture, etc.

[0051] |Y / Rh1|≦0.20 (1) |Y / Rr1|≦0.20 (2) |Y / Rr²|≦0.20 (3) From a manufacturing standpoint, it is desirable for the values ​​of equations (1) to (3) to be 0, meaning the phase shifter is planar. However, since wafer-level optics are optical systems composed of a small number of lenses and a limited number of wafers, improving imaging performance can be expected by increasing the number of curved surfaces for aberration correction. The upper limits of equations (1) to (3) indicate the range that can be manufactured in the wafer process, and it is undesirable if the values ​​of each equation exceed the upper limits because uniformity within the wafer cannot be ensured when forming the transmission reflective film and the phase shifter (e.g., λ / 4 plate).

[0052] Furthermore, it is more preferable to set the upper limits of equations (1) to (3) to 0.18, 0.15, 0.12, or 0.10.

[0053] Furthermore, in polarized reflection imaging systems, a decrease in light intensity occurs in principle because a transmissive reflective surface is used. As a result, it is important to secure light intensity by reducing the F-number of the optical system, that is, by increasing the pupil diameter. However, increasing the pupil diameter increases the size of the optical system. In miniaturizing wafer-level optics, it is necessary not only to shorten the length of the optical system in the optical axis direction but also to reduce its size in the radial direction. In particular, in polarized reflection imaging systems, the height of the ray from the optical axis increases each time the off-axis light beam is reflected. In wafer-level optics that constitute a polarized reflection imaging system, miniaturization in the radial direction of the optical system can be achieved by appropriately setting the relationship between the pupil diameter and the image height.

[0054] Specifically, when the F-number of the optical system is FNo and the focal length of the optical system is f, it is preferable that the following condition of equation (4) is satisfied.

[0055] 0.30 ≤ (FNo × Y) / f ≤ 1.75 (4) If the value of equation (4) falls below the lower limit, it becomes difficult to correct off-axis aberrations such as astigmatism, and the overall length of the optical system increases, which is undesirable. If the value of equation (4) exceeds the upper limit, the image height relative to the pupil diameter increases, and the maximum diameter of the optical system increases, which is also undesirable.

[0056] Furthermore, it is more preferable to set the lower limit of formula (4) to 0.35, 0.40, 0.45, 0.50, or 0.55. Also, it is more preferable to set the upper limit of formula (4) to 1.70, 1.65, 1.60, 1.55, or 1.50.

[0057] Furthermore, in order to miniaturize wafer-level optics, it is preferable to position the aperture diaphragm closer to the image than to the object-side surface of the optical system. Positioning the aperture diaphragm closer to the object, especially outside the object-side surface of the optical system, is undesirable because the ray height of the off-axis luminous beam becomes high near the image plane, causing the optical system to bend significantly in the radial direction.

[0058] Specifically, when Lsp is the distance along the optical axis from the aperture diaphragm to the image plane, and L is the distance along the optical axis from the optical surface closest to the object in the optical system to the image plane (total optical length), it is preferable that the following condition (5) is satisfied.

[0059] 0.2 ≤ Lsp / L ≤ 1.5 (5) If the value of equation (5) falls below the lower limit, the aperture diaphragm moves closer to the image side, and the maximum diameter of the off-axis luminous flux on the object side increases. This is undesirable because it makes aberration correction difficult and increases the size of the optical system. If the value of equation (5) exceeds the upper limit, the aperture diaphragm is positioned closer to the object side, and the ray height of the off-axis luminous flux increases near the image plane. This is undesirable because it increases the radial size of the optical system.

[0060] Furthermore, it is more preferable to set the lower limit of equation (5) to 0.25, 0.3, or 0.35. Also, it is more preferable to set the upper limit of equation (5) to 1.4, 1.3, 1.2, 1.1, 1.0, or 0.95.

[0061] Furthermore, in the optical systems of each embodiment, the first transmission reflective surface and the first phase shifter can be formed on the same surface. On the other hand, when a half-mirror is used as the second transmission reflective surface, it is preferable that the second transmission reflective surface has a curved shape. For this reason, it is preferable that the second phase shifter has a smaller curvature than the second transmission reflective surface and is formed on a surface different from the second transmission reflective surface, particularly on an optical element different from the second transmission reflective surface.

[0062] When the second phase shifter is provided on the lens surface of a lens that does not include the first and second transmission / reflection surfaces, the maximum angle of the normal to the lens surface on which the second phase shifter is formed with respect to the optical axis is denoted as θm(deg). In this case, it is preferable that the following condition of equation (6) is satisfied.

[0063] 0 ≤ θm ≤ 15 (6) The lower limit of equation (6) means that the surface on which the second phase shifter is formed is planar, and forming the second phase shifter on a planar surface is preferable because it is easy to manufacture. If the value of equation (6) exceeds the upper limit, uniformity within the wafer cannot be ensured when forming the second phase shifter, which is undesirable.

[0064] Furthermore, it is more preferable to set the upper limit of formula (6) to 14, 13, 12, 11, or 10.

[0065] In each embodiment, the optical system preferably satisfies the following condition (7), where Nc is the number of lens surfaces having power.

[0066] 2 ≤ Nc ≤ 7 (7) By keeping the lens surface having power within the range of equation (7), the overall optical length of the optical system can be shortened while effectively correcting various aberrations.

[0067] Furthermore, it is more preferable to set the upper limit of equation (7) to 6, 5, or 4. In the optical system of each embodiment, a polarization reflection imaging system can be constructed without increasing the number of optical components by stacking the first transmission reflection surface and the first phase shifter on top of each other.

[0068] Furthermore, wafer-level optics are often used in applications with relatively large fields of view. When applying a polarized reflection imaging system to an optical system with a standard to wide field of view, it is preferable to position the aperture diaphragm closer to the object than the first and second transmission reflective surfaces. This allows for good correction of aberrations such as astigmatism caused by the reflective surfaces in the region where the off-axis light beam on the image side of the aperture diaphragm is separated, thereby achieving aberration correction for the entire optical system and a reduction in the overall optical length.

[0069] In the optical system of each embodiment, miniaturization of the optical system can be achieved by appropriately setting the distance between the two transmission reflective surfaces and the aperture diaphragm. Specifically, when LS1 is the distance on the optical axis between the transmission reflective surface closer to the image side of the first and second transmission reflective surfaces and the aperture diaphragm, it is preferable that the following condition of equation (8) is satisfied.

[0070] 0.10 ≤ LS1 / L ≤ 0.75 (8) If the value of equation (8) falls below the lower limit, the height of the two off-axis rays passing through the reflective surface becomes too low, making it difficult to correct astigmatism, which is undesirable. If the value of equation (8) exceeds the upper limit, the height of the two off-axis rays passing through the reflective surface becomes too high, increasing the maximum diameter of the optical system, which is also undesirable.

[0071] Furthermore, it is more preferable to set the lower limit of equation (8) to 0.15, 0.20, or 0.25. Also, it is more preferable to set the upper limit of equation (8) to 0.70, 0.65, 0.60, or 0.55.

[0072] While aperture diaphragms in wafer-level optics can be formed on either a flat or curved surface, forming them on a flat surface is preferable because it reduces the impact of aberration variations due to positional misalignment such as manufacturing errors in the aperture diaphragm.

[0073] In the optical systems of each embodiment, aberration correction is effectively achieved by providing a large curvature to the transmitting and reflecting surface acting as a half-mirror. Since chromatic aberration does not occur on the reflecting surface and astigmatism is easily corrected, it is important to appropriately set the curvature of the transmitting and reflecting surface acting as a half-mirror. Specifically, when Rhm is the radius of curvature of the transmitting and reflecting surface with the smaller radius of curvature on the optical axis among the first and second transmitting and reflecting surfaces, it is preferable to satisfy the conditions of the following equation (9).

[0074] 1.5 ≤ |Rhm / f| ≤ 10.0 (9) If the value of equation (9) falls below the lower limit, the curvature of the reflective surface becomes too large, disrupting the balance between spherical aberration and astigmatism correction, which is undesirable. If the value of equation (9) exceeds the upper limit, the amount of astigmatism correction decreases, making it difficult to correct various aberrations in the entire optical system, which is also undesirable.

[0075] Furthermore, it is more preferable to set the lower limit of equation (9) to 2.0, 2.5, or 3.0. Also, it is more preferable to set the upper limit of equation (9) to 9.0, 8.0, 7.0, 6.0, or 5.5.

[0076] As shown in equations (1) to (3), it is preferable that the first transmission / reflection surface, the first phase shifter, and the second phase shifter used in the optical system of each embodiment have small curvature. Transmission / reflection elements and phase shifters such as λ / 4 plates are formed by laminating films or molding with a mold, but the manufacturing process may involve pressurization or heating. In this case, even a slight curvature may reduce manufacturing stability. In particular, when two optical components are formed by laminating, it is preferable to make the shape of the laminating surfaces flat to improve manufacturing stability.

[0077] In the optical systems of each embodiment, it is preferable that the effective area on at least one surface of the optical element positioned between the optical element closest to the object and the optical element closest to the image is a plane. This improves manufacturing stability.

[0078] In the optical systems of each embodiment, the phase shifter can be formed on a surface with low curvature, for example, on the surface of the cover glass of the image sensor. However, in the process of forming the λ / 4 plate on the cover glass of the image sensor, there is a risk of damage to the image sensor due to pressure, heating, etc. For this reason, it is preferable to provide the phase shifter on an optical component separate from the cover glass of the image sensor. Furthermore, in the process of forming the phase shifter on a substrate, if dust or other debris remains on the phase shifter, or if foreign matter or irregularities remain inside the phase shifter, there is a risk that the dust, foreign matter, or irregularities may be reflected in the image acquired by imaging if the phase shifter and the image sensor are in close proximity.

[0079] Therefore, when Lf is the distance on the optical axis between the image plane and the second phase shifter, which is closer to the image side, it is preferable that the following condition of equation (10) is satisfied.

[0080] 0.05 ≤ Lf / (f × FNo) ≤ 1.50 (10) If the value of equation (10) falls below the lower limit, the phase shifter and the image sensor become closer together, making it easier for foreign objects to appear in the image, which is undesirable. If the value of equation (10) exceeds the upper limit, the back focus of the optical system becomes longer, increasing the overall optical length of the optical system and making miniaturization difficult, which is also undesirable.

[0081] Furthermore, it is more preferable to set the lower limit of formula (10) to 0.06, 0.07, 0.08, 0.09, 1.00, 1.10, or 0.12. Also, it is more preferable to set the upper limit of formula (10) to 1.40, 1.30, 1.20, 1.10, or 1.05. In the optical system of each embodiment, it is preferable that the F-number FNo of the optical system satisfies the conditions of the following formula (11).

[0082] 0.7 ≤ FNo ≤ 2.8 (11) If the value of equation (11) falls below the lower limit, it becomes difficult to correct various aberrations such as spherical aberration as the aperture increases, which is undesirable. If the value of equation (11) exceeds the upper limit, the amount of light transmitted through the optical system decreases. Polarized reflection imaging systems, in principle, reduce the amount of light to 1 / 4 or 1 / 8, making it difficult to secure sufficient light for use in endoscopes or line-of-sight detection, which is undesirable.

[0083] Furthermore, it is more preferable to set the lower limit of equation (11) to 0.8, 0.9, or 0.95. Also, it is more preferable to set the upper limit of equation (11) to 2.5, 2.0, 1.8, 1.6, or 1.5.

[0084] In the optical system of each embodiment, by appropriately setting the distance between the two reflective surfaces, it is possible to achieve both aberration correction and miniaturization, particularly miniaturization in the radial direction. Specifically, when the distance on the optical axis between the first and second transmitted reflective surfaces is Lhm, it is preferable to satisfy the following condition of equation (12).

[0085] 0.05 ≤ Lhm / L ≤ 0.45 (12) If the value of equation (12) falls below the lower limit, the distance between the two reflective surfaces becomes too close, making it impossible to adequately correct aberrations at the reflective surfaces, which is undesirable. If the value of equation (12) exceeds the upper limit, the ray height of the off-axis luminous beam at the reflective surface increases, either increasing the radial size of the optical system or making it difficult to increase the power of the reflective surface, thus making good aberration correction difficult, which is also undesirable.

[0086] Furthermore, it is more preferable to set the lower limit of formula (12) to 0.06, 0.07, 0.08, 0.09, or 0.10. Also, it is more preferable to set the upper limit of formula (12) to 0.40, 0.35, 0.30, or 0.27.

[0087] In each embodiment of wafer-level optics, the optical system is often constructed by forming wiring in a high-temperature process such as reflow after the optical system and image sensor are stacked. For this reason, the resin material used to form each lens is ideally a resin material that can withstand thermal curing and UV curing processes while also having a high heat resistance temperature after the lens is formed. Therefore, in the optical system of each embodiment, the refractive index NL at the d line of the resin material that can withstand reflow and the like, used for the optical component with a curved surface, preferably satisfies the following equation (13).

[0088] 1.5 ≤ NL ≤ 1.8 (13) If the value of equation (13) falls below the lower limit, it becomes a material that is difficult to reflow, which is undesirable. If the value of equation (13) exceeds the upper limit, it becomes difficult to ensure transparency in thermosetting and UV-curing resins, or the material becomes highly dispersed, increasing chromatic aberration, which is also undesirable.

[0089] Furthermore, it is preferable to set the upper limit of (13) to 1.75, 1.7, or 1.65. Wafer-level optics, such as the optical systems in each embodiment, are generally manufactured by stacking wafers with spacers or the like outside the effective area of ​​each lens. Furthermore, since multiple lenses are formed at once in the wafer process, higher stability is required than in the lens forming process where lenses are formed one by one. In addition, phase shifters such as λ / 4 plates used in the optical systems of each embodiment, which are polarized reflection imaging systems, require a process to form them all at once across the wafer. For this reason, by appropriately setting the width of the outer region rather than the effective region in the lens where the phase shifter is formed, it is possible to achieve both miniaturization and a stable manufacturing process.

[0090] Specifically, when De is the effective diameter of the surface (lens surface, etc.) of an optical element on which at least one of the first and second phase shifters is formed, and Dmax is the maximum diameter of the region on the surface where the phase shifter is formed, it is preferable that the following condition of equation (14) is satisfied. The effective diameter is the diameter of the effective region.

[0091] 0.1 ≤ De / Dmax ≤ 0.7 (14) If the value of equation (14) falls below the lower limit, the outer shape of the wafer-level optics becomes larger, which is undesirable. If the value of equation (14) exceeds the upper limit, the width of the outer region becomes too narrow compared to the effective region of the optical component, making it difficult to achieve a stable manufacturing process, which is also undesirable.

[0092] Furthermore, it is more preferable to set the lower limit of formula (14) to 0.12, 0.13, 0.14, or 0.15. Also, it is more preferable to set the upper limit of formula (14) to 0.65, 0.60, 0.55, or 0.51.

[0093] The optical systems of each embodiment will be described in detail below. [Examples]

[0094] The optical system of Embodiment 1 shown in Figure 1 consists of a first lens unit L1, a second lens unit L2, a third lens unit L3, and a cover glass 40, arranged in order from the object side to the image side.

[0095] The first lens unit L1 is composed of a substrate 11 as a parallel plate and a lens 12, with the lens 12 positioned on the object side of the substrate 11.

[0096] The second lens unit L2 consists of an aperture diaphragm SP, a substrate 21 as a parallel plate, and a lens 22. The aperture diaphragm SP is provided on the object-side plane of the substrate 21, and the lens 22 is positioned on the image-side of the substrate 21. Furthermore, a first transmission reflective surface HM1 and a first phase shifter RT1 are positioned between the image-side plane of the substrate 21 and the object-side plane of the lens 22, in that order from the object side. A second transmission reflective surface HM2 is provided on the image-side curved surface of the lens 22.

[0097] The third lens unit L3 is composed of a lens 32. A second phase shifter RT2 is provided on the object-side plane of the lens 32. The cover glass 40 is the cover glass of the image sensor IP and is a parallel plate.

[0098] The first lens unit L1 is constructed by molding a lens 12 onto a substrate 11, which is a glass plate, using a mold and a curable resin.

[0099] In the second lens unit L2, the aperture diaphragm SP is formed on the object-side plane of the substrate 12, which is a glass plate. A first transmission-reflective film HM1 and a first phase shifter RT1 are provided on the image-side plane of the substrate 12, and a lens 22 is formed on the first phase shifter RT1 using a mold and curable resin.

[0100] The third lens unit L3 forms the object-side and image-side lens surface shapes of the lens 32 by pouring a curable resin between two lens-shaped molds arranged opposite each other and allowing it to harden. At this time, the outer peripheral region of the planar shape outside the effective area of ​​the lens 32 is also formed.

[0101] The first to third lens units L1 to L3 are each formed as a single wafer using a wafer process. The first to third lens units L1 to L3 and the cover glass 40 are then stacked using spacers and the like, which are placed outside their effective areas, to form an optical system as a wafer-level optics.

[0102] In Example 1, the first transmissive reflective surface HM1 is a polarization-selective transmissive reflective element, and the first phase shifter RT1 is a λ / 4 plate. The second transmissive reflective surface HM2 is a half mirror, and the second phase shifter RT2 is a λ / 4 plate. Light incident from the object side passes through the first transmissive reflective surface HM1, is reflected by the second transmissive reflective surface HM2, is reflected by the first transmissive reflective surface HM1 again, passes through the second transmissive reflective surface HM2, and forms an image on the image plane IP.

[0103] Placing a linear polarizer (not shown) on the image side of the second phase shifter RT2 is preferable because it can cut out unwanted polarized light. For example, by forming a linear polarizer on the object-side plane of the lens 32 and forming the second phase shifter RT2 on top of it, a good optical image with less flare can be obtained.

[0104] In the optical system of Example 1, the aperture diaphragm SP was formed on the object-side surface of the second lens unit L2, but a light beam diaphragm may be provided separately from the aperture diaphragm. For example, if a light beam diaphragm is formed on the image-side plane of the first lens unit L1, flare cut of off-axis light beams becomes possible, and aberrations of off-axis light beams can be corrected well. Such light beam diaphragms may be provided in the optical systems of Examples 2 to 8 described later, and multiple light beam diaphragms may be provided within the optical system. Furthermore, the location of the light beam diaphragm is not limited to the first lens unit L1, but may be placed in a location appropriate for off-axis light beams or effective light beams at intermediate image heights on or off-axis. [Examples]

[0105] The optical system of Embodiment 2 shown in Figure 3 consists of a cover glass 10, a first lens unit L1, a second lens unit L2, and a cover glass 40, arranged in order from the object side to the image side.

[0106] The cover glass 10 is a parallel plate positioned closest to the object in the optical system. The first lens unit L1 consists of an aperture diaphragm SP, a substrate 11 as a parallel plate, and a lens 12. The aperture diaphragm SP is provided on the object-side plane of the substrate 11, and the lens 12 is positioned on the image-side of the substrate 11. Between the image-side plane of the substrate 11 and the object-side plane of the lens 12, a first transmission reflective surface HM1 and a first phase shifter RT1 are arranged in order from the object side. Furthermore, a second transmission reflective surface HM2 is provided on the image-side lens surface of the lens 12.

[0107] The second lens unit L2 is composed of a lens 22. A second phase shifter RT2 is provided on the object-side plane of the lens 22. The cover glass 40 is the cover glass of the image sensor IP and is a parallel plate.

[0108] In this embodiment as well, similar to Embodiment 1, after molding each lens unit using a mold, the cover glass 10, the first and second lens units L1 and L2, and the cover glass 40 are stacked using spacers and the like that placed outside the effective area to form an optical system as a wafer-level optics.

[0109] In this embodiment, the first transmissive reflective surface HM1, the first phase shifter RT1, the second transmissive reflective surface HM2, and the second phase shifter RT2 are the same polarizing elements as in Embodiment 1, and the optical path through which light from the object passes is also the same as the optical system in Embodiment 1. In this embodiment, as in Embodiment 1, a linear polarizer may be placed on the image side of the second phase shifter RT2. [Examples]

[0110] The optical system of Embodiment 3 shown in Figure 5 consists of a first lens unit L1, a second lens unit L2, a third lens unit L3, and a cover glass 40, arranged in order from the object side to the image side.

[0111] The first lens unit L1 consists of a substrate 11 as a parallel plate and a lens 12. The lens 12 is positioned on the object side of the substrate 11.

[0112] The second lens unit L2 consists of an aperture diaphragm SP, a substrate 21 as a parallel plate, and a lens 22. The aperture diaphragm SP is provided on the object-side plane of the substrate 21. The lens 22 is positioned on the image side of the substrate 21. Furthermore, a first transmission reflective surface HM1 and a first phase shifter RT1 are positioned between the image-side plane of the substrate 21 and the object-side plane of the lens 22, in order from the object side. A second transmission reflective surface HM2 is provided on the image-side curved surface of the lens 22.

[0113] The third lens unit L3 is composed of a lens 32. A second phase shifter RT2 is provided on the object-side plane of the lens 32. The cover glass 40 is the cover glass of the image sensor IP and is a parallel plate.

[0114] In this embodiment as well, similar to Embodiment 1, after molding each lens unit using a mold, the first to third lens units L1 to L3 and the cover glass 40 are stacked using spacers and the like that placed outside the effective area to form an optical system as a wafer-level optics.

[0115] In this embodiment, the first transmissive reflective surface HM1, the first phase shifter RT1, the second transmissive reflective surface HM2, and the second phase shifter RT2 are the same polarizing elements as in Embodiment 1, and the optical path through which light from the object passes is also the same as the optical system in Embodiment 1. In this embodiment, as in Embodiment 1, a linear polarizer may be placed on the image side of the second phase shifter RT2. [Examples]

[0116] The optical system of Embodiment 4 shown in Figure 7 consists of a first lens unit L1, a second lens unit L2, a third lens unit L3, and a cover glass 40, arranged in order from the object side to the image side.

[0117] The first lens unit L1 is composed of a lens 12.

[0118] The second lens unit L2 consists of an aperture diaphragm SP, a lens 22, and a lens 23. The aperture diaphragm SP is located on the image-side plane of lens 22. Lens 23 is bonded to the image-side plane of lens 22. Furthermore, a first transmission / reflection surface HM1 and a first phase shifter RT1 are arranged between the image-side plane of lens 22 and the object-side plane of lens 23, in order from the object side.

[0119] The third lens unit L3 is composed of a lens 32. The object-side surface of the lens 32 is flat. A second transmission / reflection surface HM2 is provided on the image-side curved surface of the lens 32. The cover glass 40 is the cover glass of the image sensor IP and is a parallel plate. A second phase shifter RT2 is provided on the object-side flat surface of the cover glass 40.

[0120] In this embodiment as well, similar to Embodiment 1, after molding each lens unit using a mold, the first to third lens units L1 to L3 and the cover glass 40 are stacked using spacers and the like that placed outside the effective area to form an optical system as a wafer-level optics.

[0121] In this embodiment, the first transmissive reflective surface HM1, the first phase shifter RT1, the second transmissive reflective surface HM2, and the second phase shifter RT2 are the same polarizing elements as in Embodiment 1, and the optical path through which light from the object passes is also the same as the optical system in Embodiment 1. In this embodiment, as in Embodiment 1, a linear polarizer may be placed on the image side of the second phase shifter RT2. [Examples]

[0122] The optical system of Embodiment 5 shown in Figure 9 consists of a cover glass 10, a first lens unit L1, a second lens unit L2, a third lens unit L3, and a cover glass 40, arranged in order from the object side. In the optical systems of Embodiments 1 to 4, the first and second phase shifters were arranged on a plane, but the optical systems of Embodiments 5 and 7 have a different configuration.

[0123] The aperture diaphragm SP is provided on the image-side plane of the cover glass 10, which is a parallel plate. The first lens unit L1 is composed of a lens 12. The second phase shifter RT2 is provided on the object-side curved surface (lens surface) of the lens 12.

[0124] The second lens unit L2 is composed of a lens 22. A second transmission / reflection surface HM2 is provided on the object-side curved surface of the lens 22.

[0125] The third lens unit L3 is composed of a substrate 32 which is a parallel plate. On the object-side plane of the substrate 32, the first phase shifter RT1 and the first transmission / reflection surface HM1 are provided in order from the object side. The cover glass 40 is the cover glass of the image sensor IP and is a parallel plate.

[0126] In this embodiment, as in Embodiment 1, each lens unit is molded using a mold. In this case, by reducing the curvature of the object-side lens surface of the lens 12, the second phase shifter RT2 can be stably formed on the entire surface of the wafer using a wafer process. Subsequently, the cover glass 10, the first to third lens units L1 to L3, and the cover glass 40 are stacked using spacers and the like that placed outside the effective area to form an optical system as a wafer-level optics.

[0127] In this embodiment, the first transmissive reflective surface HM1, the first phase shifter RT1, the second transmissive reflective surface HM2, and the second phase shifter RT2 are the same polarizing elements as in Embodiment 1. Light incident from the object side passes through the second transmissive reflective surface HM2, is reflected by the first transmissive reflective surface HM1, is reflected by the second transmissive reflective surface HM2, passes through the first transmissive reflective surface HM1, and forms an image on the image plane IP.

[0128] In this embodiment, it is preferable to place the linear polarizing element on the object side of the second phase shifter RT2. For example, by forming the second phase shifter RT2 on the object-side plane of the lens 12 and stacking a linear polarizing plate on top of it, a good optical image with less flare can be obtained. [Examples]

[0129] The optical system of Embodiment 6 shown in Figure 11 consists of a cover glass 10, a first lens unit L1, a second lens unit L2, a third lens unit L3, and a cover glass 40, arranged in order from the object side.

[0130] The aperture diaphragm SP is provided on the image-side plane of the cover glass 10, which is a parallel plate. The first lens unit L1 is composed of a lens 12. The second phase shifter RT2 is provided on the image-side plane of the lens 12.

[0131] The second lens unit L2 is composed of a lens 22. A second transmission / reflection surface HM2 is provided on the object-facing curved surface (lens surface) of the lens 22.

[0132] The third lens unit L3 is composed of a substrate 32 which is a parallel plate. On the object-side plane of the substrate 32, the first phase shifter RT1 and the first transmission / reflection surface HM1 are provided in order from the object side. The cover glass 40 is the cover glass of the image sensor IP and is a parallel plate.

[0133] In this embodiment as well, similar to Embodiment 1, after molding each lens unit using a mold, the cover glass 10, the first to third lens units L1 to L3, and the cover glass 40 are stacked using spacers and the like that placed outside the effective area to form an optical system as a wafer-level optics.

[0134] In this embodiment, the first transmissive reflective surface HM1, the first phase shifter RT1, the second transmissive reflective surface HM2, and the second phase shifter RT2 are the same polarizing elements as in Embodiment 1, and the optical path through which light from the object side passes is the same as the optical system in Embodiment 5. In this embodiment as well, it is preferable to place a linear polarizing element on the object side of the second phase shifter RT2. [Examples]

[0135] The optical system of Embodiment 7 shown in Figure 13 consists of a cover glass 10, a first lens unit L1, a second lens unit L2, a third lens unit L3, and a cover glass 40, arranged in order from the object side.

[0136] The first lens unit L1 is composed of a substrate 11 which is a parallel plate, a lens 12, and an aperture diaphragm SP. The lens 12 is provided on the object side of the substrate 11, and the aperture diaphragm SP is provided on the image-side plane of the substrate 11. Furthermore, a second phase shifter RT2 is provided on the object-side plane of the substrate 11.

[0137] The second lens unit L2 is composed of a lens 22. A second transmission reflective surface HM2 is provided on the object-side curved surface (lens surface) of the lens 22. In addition, a first phase shift element RT1 and a first transmission reflective surface HM1 are provided on the image-side curved surface of the lens 22, in order from the object side.

[0138] The third lens unit L3 consists of a lens 32. The cover glass 40 is the cover glass for the image sensor IP and is a parallel plate.

[0139] In this embodiment as well, each lens unit is molded using a mold, similar to Embodiment 1. In this case, by reducing the curvature of the image-side lens surface of lens 22, the first phase shifter RT1 can be stably formed on the entire surface of the wafer using a wafer process. Subsequently, the cover glass 10, the first to third lens units L1 to L3, and the cover glass 40 are stacked using spacers and the like that placed outside the effective area to form an optical system as a wafer-level optics.

[0140] In this embodiment, the first transmissive reflective surface HM1, the first phase shifter RT1, the second transmissive reflective surface HM2, and the second phase shifter RT2 are the same polarizing elements as in Embodiment 1, and the optical path through which light from the object side passes is the same as the optical system in Embodiment 5. In this embodiment as well, it is preferable to place a linear polarizing element on the object side of the second phase shifter RT2. [Examples]

[0141] The optical system of Embodiment 8 shown in Figure 15 consists of a cover glass 10, a first lens unit L1, a second lens unit L2, and a cover glass 40, arranged in order from the object side.

[0142] The first lens unit L1 is composed of a substrate 11 which is a parallel plate, a lens 12, and an aperture diaphragm SP. The lens 12 is provided on the object side of the substrate 11, and the aperture diaphragm SP is provided on the image-side plane of the substrate 11. Furthermore, a second phase shifter RT2 is provided on the object-side plane of the substrate 11.

[0143] The second lens unit L2 consists of a lens 22, a substrate 21 which is a parallel plate, and a lens 23. The lens 22 is provided on the object side of the substrate 21, and the lens 23 is provided on the image side. A second transmission reflective surface HM2 is provided on the curved surface (lens surface) of the lens 22 on the object side. In addition, a first phase shifter RT1 and the first transmission reflective surface HM1 are provided on the plane of the image side of the lens 22, in order from the object side.

[0144] The cover glass 40 is the cover glass for the image sensor IP and is a parallel plate.

[0145] In this embodiment as well, similar to Embodiment 1, after molding each lens unit using a mold, the cover glass 10, the first and second lens units L1 and L2, and the cover glass 40 are stacked using spacers and the like that placed outside the effective area to form an optical system as a wafer-level optics.

[0146] In this embodiment, the first transmissive reflective surface HM1, the first phase shifter RT1, the second transmissive reflective surface HM2, and the second phase shifter RT2 are the same polarizing elements as in Embodiment 1, and the optical path through which light from the object side passes is the same as the optical system in Embodiment 5. In this embodiment as well, it is preferable to place a linear polarizing element on the object side of the second phase shifter RT2.

[0147] The following shows numerical examples 1 to 8 corresponding to each of the examples 1 to 8. In each numerical example, the surface number i indicates the order of the surfaces counted from the object side. r is the radius of curvature of the i-th surface (mm), d is the lens thickness or air gap on the optical axis between the i-th and (i+1)-th surfaces (mm), and nd is the refractive index of the optical material at the d-line between the i-th and (i+1)-th surfaces. νd is the Abbe number with respect to the d-line of the optical material between the i-th and (i+1)-th surfaces.

[0148] The Abbe number νd, with respect to the d line, is expressed as νd = (Nd-1) / (NF-NC), where Nd, NF, and NC are the refractive indices of the Fraunhofer lines d (587.6 nm), F (486.1 nm), and C (656.3 nm), respectively.

[0149] The focal length f (mm) is the value when the lens is in focus on an object at infinity. BF is the back focus, which is the air-equivalent distance along the optical axis from the final surface closest to the image in the optical system to the image plane. The total length of the lens is the distance along the optical axis from the first surface closest to the object to the final surface of the optical system, plus the back focus, and is also called the total optical length.

[0150] The asterisk (*) next to the surface number indicates that the surface has an aspherical shape. The aspherical shape is expressed by the following formula, where x is the displacement in the direction of the optical axis at a height h from the optical axis, relative to the surface vertex, R is the radius of paraxial curvature, K is the cone constant, and Ai (i=2,4,6,8,…) are the aspherical coefficients of each order. Note that the cone constant and aspherical coefficients "e±M" are multiplied by 10⁻¹⁴. ±M This means that the radius of curvature for each condition regarding the aspherical surface is calculated using the value of R.

[0151]

number

[0152] In each numerical example, (aperture) indicates the aperture diaphragm. The effective diameter indicates the diameter of the effective region through which light contributing to image formation passes on each surface. (Numerical example 1) Unit: mm Surface data Face number rd nd νd Effective diameter 1* 1.6332 0.370 1.51100 57.0 1.82 2 ∞ 0.250 1.51680 64.2 1.71 3 ∞ 0.331 1.47 4 (aperture) ∞ 0.248 1.51680 64.2 0.94 5 ∞ 0.292 1.51100 57.0 1.55 6* -4.3312 -0.292 1.51100 57.0 1.64 7 ∞ 0.292 1.51100 57.0 1.55 8* -4.3312 0.042 1.64 9 ∞ 0.186 1.59000 31.0 1.69 10* -3.7238 0.094 1.75 11 ∞ 0.236 1.51680 64.2 1.83 12 ∞ 0.020 1.99 Image plane ∞ Aspherical data Front page K = 0.00000e+00, A4=-3.20510e-02, A6=-1.58626e-02 Side 6 K = 0.00000e+00, A4= 1.12785e-02, A6= 7.76210e-03 Side 8 K = 0.00000e+00 ,A4= 1.12785e-02, A6= 7.76210e-03 Side 10 K = 0.00000e+00, A4= 3.11132e-01 ,A6=-2.76747e-01, A8= 1.94275e-01 Focal length 1.177 F-number 1.000 Half-angle (°): 40.002 Image height 1.000 Lens length 2.069 BF 0.020 (Numerical example 2) Unit: mm Surface data Face number rd nd νd Effective diameter 1 ∞ 0.297 1.51680 64.2 1.56 2 ∞ 0.576 1.25 3 (aperture) ∞ 0.249 1.51680 64.2 1.25 4 ∞ 0.511 1.51100 57.0 2.05 5* -4.9094 -0.511 1.51100 57.0 2.15 6 ∞ 0.511 1.51100 57.0 2.05 7* -4.9094 0.036 2.15 8 ∞ 0.551 1.51100 57.0 2.17 9* -1.2657 0.040 2.19 10 ∞ 0.501 1.51680 64.2 2.09 11 ∞ 0.019 2.01 Image plane ∞ Aspherical data 5th page K = 0.00000e+00, A4= 8.25908e-03, A6=-2.81294e-03 Side 7 K = 0.00000e+00, A4= 8.25908e-03, A6=-2.81294e-03 9th page K = 0.00000e+00, A4= 3.45758e-01, A6=-2.37483e-01, A8= 1.14847e-01 Focal length 1.246 F-number 1.000 Half-angle (°): 45.096 Image height 1.000 Lens length 2.780 BF 0.019 (Numerical example 3) Unit: mm Surface data Face number rd nd νd Effective diameter 1 ∞ 0.200 1.51680 64.2 1.48 2 (aperture) ∞ 0.100 1.51100 57.0 1.27 3* -9.1871 0.316 1.36 4 ∞ 0.199 1.51680 64.2 2.02 5 ∞ 0.347 1.51100 57.0 2.43 6* -5.3501 -0.347 1.51100 57.0 2.45 7 ∞ 0.347 1.51100 57.0 2.43 8* -5.3501 0.050 2.45 9 ∞ 0.292 1.51100 57.0 2.32 10* -2.1405 0.049 2.28 11 ∞ 0.905 1.51680 64.2 2.20 12 ∞ 0.020 2.01 Image plane ∞ Aspherical data 3rd page K = 0.00000e+00, A4= 4.91305e-02, A6=-2.94331e-02, A8= 8.41495e-02 Side 6 K = 0.00000e+00, A4= 4.05400e-03, A6=-5.21411e-03, A8= 3.90705e-04 Side 8 K = 0.00000e+00, A4= 4.05400e-03, A6=-5.21411e-03, A8= 3.90705e-04 Side 10 K = 0.00000e+00 ,A4= 7.86580e-02, A6=-1.36331e-02, A8= 2.07391e-02 Focal length 1.265 F-number 1.000 Half-angle (°): 44.994 Image height 1.000 Lens length 2.477 BF 0.020 (Numerical example 4) Unit: mm Surface data Face number rd nd νd Effective diameter 1* 1.6167 0.709 1.51100 57.0 2.11 2 ∞ 0.528 1.69 3 -2.6785 0.144 1.59000 31.0 1.22 4 (aperture) ∞ 0.200 1.51100 57.0 1.18 5* -14.4948 0.089 1.89 6 ∞ 0.291 1.63000 24.0 1.92 7* -5.3414 -0.291 1.63000 24.0 1.94 8 ∞ -0.089 1.92 9* -14.4948 -0.200 1.51100 57.0 1.89 10 ∞ 0.200 1.51100 57.0 1.85 11* -14.4948 0.089 1.89 12 ∞ 0.291 1.63000 24.0 1.92 13* -5.3414 0.090 1.94 14 ∞ 0.200 1.51680 64.2 1.96 15 ∞ 0.020 1.98 Image plane ∞ Aspherical data Front page K = 0.00000e+00, A4=-1.60722e-03, A6=-4.91427e-03 5th page K = 0.00000e+00, A4=-3.57407e-02, A6= 7.24758e-03 Side 7 K = 0.00000e+00, A4= 2.21179e-02, A6= 1.76019e-03 9th page K = 0.00000e+00, A4=-3.57407e-02, A6= 7.24758e-03 Page 11 K = 0.00000e+00, A4=-3.57407e-02, A6= 7.24758e-03 Page 13 K = 0.00000e+00, A4= 2.21179e-02, A6= 1.76019e-03 Focal length 1.677 F-number 1.000 Half-angle (°): 29.750 Image height 1.000 Lens length 2.271 BF 0.020 (Numerical example 5) Unit: mm Surface data Face number rd nd νd Effective diameter 1 ∞ 0.300 1.51680 64.2 1.03 2 ∞ 0.005 1.03 3 (aperture) ∞ 0.044 1.03 4* 6.0000 0.236 1.52290 50.3 1.03 5* 610.6653 0.010 1.24 6* 4.5224 0.196 1.52290 50.3 2.03 7* -24.2620 0.236 2.01 8 ∞ -0.236 2.01 9* -24.2620 -0.196 1.52290 50.3 2.01 10* 4.5224 0.196 1.52290 50.3 2.03 11* -24.2620 0.236 2.01 12 ∞ 0.296 1.51680 64.2 2.01 13 ∞ 0.217 2.00 14 ∞ 0.300 1.51680 64.2 2.00 15 ∞ 0.046 2.00 Image plane ∞ Aspherical data Side 4 K = 0.00000e+00, A4=-1.40474e-01, A6=-7.17880e-01, A8= 8.21507e-01, A10 = -3.55134e + 00 5th page K = 0.00000e+00, A4= 2.92872e-03, A6=-1.57608e+00, A8= 2.80237e+00, A10 = -3.82436e + 00 Side 6 K = 0.00000e+00, A4=-9.11629e-02, A6= 1.96323e-01, A8=-2.01147e-01, A10= 7.36729e-02, A12= 5.63879e-03 Side 7 K = 0.00000e+00, A4=-2.19409e-01, A6= 6.24596e-01, A8=-6.92580e-01, A10 = 3.02219e-01 9th page K = 0.00000e+00, A4=-2.19409e-01, A6= 6.24596e-01, A8=-6.92580e-01, A10 = 3.02219e-01 Side 10 K = 0.00000e+00, A4=-9.11629e-02, A6= 1.96323e-01, A8=-2.01147e-01, A10= 7.36729e-02, A12= 5.63879e-03 Page 11 K = 0.00000e+00, A4=-2.19409e-01, A6= 6.24596e-01, A8=-6.92580e-01, A10 = 3.02074e-01 Focal length 1.234 F-number 1,200 Half-angle (°): 45.015 Image height 1.000 Lens length 1.885 BF 0.046 (Numerical example 6) Unit: mm Surface data Face number rd nd νd Effective diameter 1 ∞ 0.300 1.51680 64.2 0.92 2 ∞ 0.005 0.93 3 (aperture) ∞ 0.024 0.93 4* 1.8702 0.191 1.51100 57.0 1.17 5 ∞ 0.638 1.23 6* 3.7680 0.212 1.51100 57.0 2.17 7* 555.4841 0.038 2.17 8 ∞ -0.038 2.13 9* 555.4841 -0.212 1.51100 57.0 2.13 10* 3.7680 0.212 1.51100 57.0 2.17 11* 555.4841 0.038 2.17 12 ∞ 0.402 1.51680 64.2 2.13 13 ∞ 0.130 2.13 14 ∞ 0.200 1.51680 64.2 2.03 15 ∞ 0.020 2.05 Image plane ∞ Aspherical data Side 4 K = 0.00000e+00, A4=-3.72792e-02, A6= 3.75079e-01, A8=-1.10736e+00, A10 = 1.19517e+00 Side 6 K = 0.00000e+00, A4=-1.54225e-01, A6= 3.65682e-01, A8=-3.64765e-01, A10= 1.14835e-01, A12= 5.63879e-03 Side 7 K = 0.00000e+00, A4=-2.65705e-01, A6= 7.48177e-01, A8=-8.18422e-01, A10 = 3.05930e-01 9th page K = 0.00000e+00, A4=-2.65705e-01, A6= 7.48177e-01, A8=-8.18422e-01, A10 = 3.05930e-01 Side 10 K = 0.00000e+00, A4=-1.54225e-01, A6= 3.65682e-01, A8=-3.64765e-01, A10= 1.14835e-01, A12= 5.63879e-03 Page 11 K = 0.00000e+00, A4=-2.65705e-01, A6= 7.48177e-01, A8=-8.18422e-01, A10 = 3.05785e-01 Focal length 1.106 F-number 1,200 Half-angle (°): 44.988 Image height 1.000 Lens length 2.160 BF 0.020 (Numerical example 7) Unit: mm Surface data Face number rd nd νd Effective diameter 1 ∞ 0.300 1.51633 64.1 1.21 2 ∞ 0.019 0.86 3* 1.5023 0.262 1.51100 57.0 0.79 4 ∞ 0.300 1.51633 64.1 0.75 5 (aperture) ∞ 0.217 0.70 6* 4.7958 0.268 1.51100 57.0 1.66 7 -19.9999 -0.268 1.51100 57.0 1.76 8* 4.7958 0.268 1.51100 57.0 1.66 9 -19.9999 0.069 1.76 10 ∞ 0.199 1.51100 57.0 1.84 11* -1.2339 0.043 1.91 12 ∞ 0.300 1.51630 64.1 1.94 13 ∞ 0.020 1.99 Image plane ∞ Aspherical data 3rd page K = 0.00000e+00, A4=-2.81684e-01, A6= 2.78610e+00, A8=-1.90813e+01, A10 = 4.59089e+01 Side 6 K = 0.00000e+00, A4= 3.86423e-02, A6=-2.20030e-01, A8= 3.65002e-01, A10 = -2.55735e-01 Side 8 K = 0.00000e+00, A4= 3.86423e-02, A6=-2.20030e-01, A8= 3.65002e-01, A10 = -2.55735e-01 Page 11 K = 0.00000e+00, A4= 1.51067e+00, A6=-2.40038e+00, A8= 2.26514e+00, A10 = -9.50613e-01 Focal length 0.945 F-number 1,200 Half-angle (°): 49.944 Image height 1.000 Lens length 1.996 BF 0.020 (Numerical example 8) Unit: mm Surface data Face number rd nd νd Effective diameter 1 ∞ 0.300 1.51633 64.1 1.07 2 ∞ 0.019 0.68 3* 2.1966 0.136 1.51100 57.0 0.68 4 ∞ 0.300 1.51633 64.1 0.67 5 (aperture) ∞ 0.235 0.64 6* 3.7739 0.303 1.51100 57.0 1.89 7 ∞ -0.303 1.51100 57.0 1.94 8* 3.7739 0.303 1.51100 57.0 1.89 9 ∞ 0.194 1.51633 64.1 1.94 10 ∞ 0.248 1.51100 57.0 2.00 11* -1.3052 0.043 2.04 12 ∞ 0.300 1.51630 64.1 2.02 13 ∞ 0.020 2.00 Image surface ∞ Aspherical data Third surface K = 0.00000e+00, A4=-3.33088e-01, A6= 5.38088e+00, A8=-4.97978e+01, A10= 1.64527e+02 Sixth surface K = 0.00000e+00, A4= 1.51298e-02, A6=-8.51722e-02, A8= 1.12788e-01, A10=-6.23417e-02 Eighth surface K = 0.00000e+00, A4= 1.51298e-02, A6=-8.51722e-02, A8= 1.12788e-01, A10=-6.23417e-02 Eleventh surface K = 0.00000e+00, A4= 1.02526e+00, A6=-1.29804e+00, A8= 1.01519e+00, A10=-3.69473e-01 Focal length 0.953 F-number 1.400 Half angle of view (°) 54.963 Image height 1.000 Total lens length 2.097 BF 0.020 Table 1 summarizes the numerical values related to the aforementioned formulas (1) to (14) in each numerical example. In Table 1, De1 corresponding to De in formula (14) represents the effective diameter of the first phase shifter, and De2 represents the effective diameter of the second phase shifter. The optical system of each numerical example satisfies all the conditions of formulas (1) to (14).

[0153]

Table 1

[0154] Figures 2, 4, 6, 8, 10, 12, 14, and 16 show the longitudinal aberrations (spherical aberration, astigmatism, distortion, and chromatic aberration) of the optical systems of numerical examples 1 to 8 when focused on an object at infinity. In the spherical aberration diagram, Fno indicates the F number, the solid line shows the spherical aberration at the d line (wavelength 587.6 nm), the dashed line shows the spherical aberration at the g line (wavelength 435.8 nm), the dashed line shows the spherical aberration at the C line (wavelength 656.3 nm), and the long dashed line shows the spherical aberration at the F line (wavelength 486.1 nm). In the astigmatism diagram, the solid line S shows the astigmatism at the sagittal image plane at the d line (design wavelength), and the dashed line M shows the astigmatism at the meridional image plane at the design wavelength. The distortion diagram shows the distortion at the design wavelength. The chromatic aberration diagram shows the lateral chromatic aberration at the g, C, and F lines. Y is the image height.

[0155] As explained above, in each embodiment (numerical example), various aberrations in the visible wavelength range can be well corrected, and a compact optical system with a short optical length and small maximum diameter has been realized.

[0156] [Imaging device 1] Figure 19 shows a smartphone 70 as an electronic device incorporating an imaging device using the optical systems of Examples 1 to 8. The smartphone 70 has an imaging device 71 as a front camera module. The imaging device 71 has an imaging optical system 72 as an optical system of any of Examples 1 to 8, and an image sensor 73 that converts the optical image formed by the imaging optical system 72 into an image sensor (images the subject).

[0157] In this way, by using the optical systems of each embodiment in imaging devices incorporated into electronic devices such as smartphones, it is possible to realize electronic devices that are compact yet capable of acquiring high-quality images.

[0158] [Imaging device 2] Figure 20 shows an endoscope 100 as an imaging device using the optical systems of Examples 1 to 8. The endoscope 100 has a camera head 120 and an electrical cable 150. The camera head 120 has a lens housing 121 equipped with an imaging optical system as one of the optical systems of Examples 1 to 8, an image sensor (image element) 122, and a ceramic substrate 123. The wiring of the electrical cable 150 is connected to the image sensor 122 via the ceramic substrate 123.

[0159] Thus, by using the optical systems of each embodiment in imaging devices such as endoscopes, it is possible to realize a compact imaging device with a simple configuration that sufficiently suppresses various aberrations and is easy to manufacture.

[0160] The above embodiments include the following configuration.

[0161] (Composition 1) An optical system having a first transmission reflecting surface, a first phase shifter, a second transmission reflecting surface, and a second phase shifter arranged in order, When Rh1 is the radius of curvature of the first transmission / reflection surface on the optical axis, Rr1 is the radius of curvature of the surface on which the first phase shifter is provided on the optical axis, Rr2 is the radius of curvature of the surface on which the second phase shifter is provided on the optical axis, f is the focal length of the optical system, FNo is the F-number, and Y is the maximum image height, |Y / Rh1|≦0.20 |Y / Rr1|≦0.20 |Y / Rr2|≦0.20 0.30 ≤ (FNo × Y) / f ≤ 1.75 An optical system characterized by satisfying the following conditions. (Configuration 2) When Lsp is the distance along the optical axis from the aperture diaphragm to the image plane, and L is the distance along the optical axis from the optical surface closest to the object to the image plane, 0.2 ≤ Lsp / L ≤ 1.5 The optical system according to configuration 1, characterized by satisfying the following conditions. (Composition 3) The second phase shifter is provided on the lens surface of a lens that does not include the first and second transmission / reflection surfaces, and when the maximum angle of the normal to the lens surface with respect to the optical axis is θm (deg), 0 ≤ θm ≤ 15 The optical system according to configuration 1 or 2, characterized by satisfying the following conditions. (Composition 4) When the number of power-bearing lens surfaces in the optical system is Nc, 2 ≤ Nc ≤ 7 An optical system according to any one of configurations 1 to 3, characterized by satisfying the following conditions. (Composition 5) The optical system according to any one of configurations 1 to 4, characterized in that the first transmission reflective surface and the first phase shifter are stacked and arranged relative to each other. (Composition 6) The optical system according to any one of configurations 1 to 5, characterized in that the aperture diaphragm is positioned on the object side of the first and second transmission and reflection surfaces. (Composition 7) When LS1 is the distance along the optical axis between the first and second transmission-reflecting surfaces and the transmission-reflecting surface located on the image side, and the aperture diaphragm, and L is the distance along the optical axis from the optical surface closest to the object to the image plane, 0.10 ≤ LS1 / L ≤ 0.75 An optical system according to any one of configurations 1 to 6, characterized by satisfying the following conditions. (Composition 8) When Rhm is the radius of curvature of the first and second transmissive reflective surfaces that has a smaller radius of curvature along the optical axis, 1.5 ≤ |Rhm / f| ≤ 10.0 An optical system according to any one of configurations 1 to 7, characterized by satisfying the following conditions. (Composition 9) The optical system according to any one of configurations 1 to 8, characterized in that the effective area of ​​at least one surface of an optical element disposed between the optical element closest to the object and the optical element closest to the image is planar. (Composition 10) When Lf represents a distance on an optical axis between the image-side phase shifter of the first phase shifter and the second phase shifter and an image plane, 0.05≦Lf / (f×FNo)≦1.50 The optical system according to any one of Configurations 1 to 9, satisfying the following condition. (Configuration 11) 0.7≦FNo≦2.8 The optical system according to any one of Configurations 1 to 10, satisfying the following condition. (Configuration 12) When Lhm represents a distance on an optical axis between the first transmission-reflection surface and the second transmission-reflection surface, and L represents a distance on an optical axis from an optical surface closest to an object side to the image plane, 0.05≦Lhm / L≦0.45 The optical system according to any one of Configurations 1 to 11, satisfying the following condition. (Configuration 13) When NL represents a refractive index at d-line of a lens having a curved surface in the optical system, 1.5≦NL≦1.8 The optical system according to any one of Configurations 1 to 12, satisfying the following condition. (Configuration 14) At least one of the first phase shifter and the second phase shifter is formed on a surface of an optical member, When De represents an effective diameter of the surface, and Dmax represents a maximum diameter of a region where the phase shifter is formed on the surface, 0.1≦De / Dmax≦0.7 The optical system according to any one of Configurations 1 to 13, satisfying the following condition. (Configuration 15) The optical system according to any one of Configurations 1 to 14, wherein light incident on the optical system from an object side passes through the first transmission-reflection surface, is reflected by the second transmission-reflection surface, is reflected by the first transmission-reflection surface, passes through the second transmission-reflection surface, and reaches the image plane. (Configuration 16) An optical system according to any one of configurations 1 to 14, characterized in that light incident on the optical system from the object side passes through the second transmission reflective surface, is reflected by the first transmission reflective surface, is reflected by the second transmission reflective surface, passes through the first transmission reflective surface, and reaches the image plane. (Composition 17) An optical system having a first transmission reflecting surface, a first phase shifter, a second transmission reflecting surface, and a second phase shifter arranged in order, When the radius of curvature of the first transmissive / reflective surface on the optical axis is Rh1, the radius of curvature of the surface on which the first phase shifter is provided is Rr1, and the radius of curvature of the surface on which the second phase shifter is provided is Rr2, |Y / Rh1|≦0.20 |Y / Rr1|≦0.20 |Y / Rr2|≦0.20 An optical system characterized by satisfying the following conditions. (Composition 18) The optical system described in any one of configurations 1 to 17, An imaging device characterized by having an image sensor that images an object through the optical system. The embodiments described above are merely representative examples, and various modifications and changes can be made to each embodiment when implementing the present invention. [Explanation of Symbols]

[0162] HM1 1st transmissive reflective surface HM2 2nd transmissive reflective surface RT1 1st phase shifter RT2 2nd phase shifter SP aperture diaphragm

Claims

1. An optical system having a first transmission reflecting surface, a first phase shifter, a second transmission reflecting surface, and a second phase shifter arranged in order, When Rh1 is the radius of curvature of the first transmission / reflection surface on the optical axis, Rr1 is the radius of curvature of the surface on which the first phase shifter is provided on the optical axis, Rr2 is the radius of curvature of the surface on which the second phase shifter is provided on the optical axis, f is the focal length of the optical system, FNo is the F-number, and Y is the maximum image height, |Y / Rh1|≦0.20 |Y / Rr1|≦0.20 |Y / Rr2|≦0.20 0.30 ≤ (FNo × Y) / f ≤ 1.75 An optical system characterized by satisfying the following conditions.

2. When Lsp is the distance along the optical axis from the aperture diaphragm to the image plane, and L is the distance along the optical axis from the optical surface closest to the object to the image plane, 0.2 ≤ Lsp / L ≤ 1.5 The optical system according to claim 1, characterized in that it satisfies the following conditions.

3. The second phase shifter is provided on the lens surface of a lens that does not include the first and second transmission / reflection surfaces, and when the maximum angle of the normal to the lens surface with respect to the optical axis is θm (deg), 0 ≤ θm ≤ 15 The optical system according to claim 1, characterized in that it satisfies the following conditions.

4. When the number of power-bearing lens surfaces in the optical system is Nc, 2 ≤ Nc ≤ 7 The optical system according to claim 1, characterized in that it satisfies the following conditions.

5. The optical system according to claim 1, characterized in that the first transmission / reflection surface and the first phase shifter are stacked and arranged relative to each other.

6. The optical system according to claim 1, characterized in that the aperture diaphragm is positioned on the object side of the first and second transmission and reflection surfaces.

7. When LS1 is the distance along the optical axis between the first and second transmission-reflecting surfaces and the transmission-reflecting surface located on the image side, and the aperture diaphragm, and L is the distance along the optical axis from the optical surface closest to the object to the image plane, 0.10 ≤ LS1 / L ≤ 0.75 The optical system according to claim 1, characterized in that it satisfies the following conditions.

8. When Rhm is the radius of curvature of the first and second transmissive reflective surfaces that has a smaller radius of curvature along the optical axis, 1.5≦|Rhm / f|≦10.0 The optical system according to claim 1, characterized in that it satisfies the following conditions.

9. The optical system according to claim 1, characterized in that the effective area of ​​at least one surface of an optical element disposed between the optical element closest to the object and the optical element closest to the image is planar.

10. When Lf is the distance along the optical axis between the image-side phase shifter of the first phase shifter and the image plane, 0.05 ≤ Lf / (f × FNo) ≤ 1.50 The optical system according to claim 1, characterized in that it satisfies the following conditions.

11. 0.7 ≤ FNo ≤ 2.8 The optical system according to claim 1, characterized in that it satisfies the following conditions.

12. When Lhm is the distance along the optical axis between the first and second transmission / reflection surfaces, and L is the distance along the optical axis from the optical surface closest to the object to the image plane, 0.05 ≤ Lhm / L ≤ 0.45 The optical system according to claim 1, characterized in that it satisfies the following conditions.

13. When the refractive index of the curved lens in the optical system is denoted as NL at the d-line, 1.5 ≤ NL ≤ 1.8 The optical system according to claim 1, characterized in that it satisfies the following conditions.

14. At least one of the first and second phase shifters is formed on the surface of the optical member. When the effective diameter of the surface is De, and the maximum diameter of the region on the surface where the phase shifter is formed is Dmax, 0.1 ≤ De / Dmax ≤ 0.7 The optical system according to claim 1, characterized in that it satisfies the following conditions.

15. The optical system according to claim 1, characterized in that light incident on the optical system from the object side passes through the first transmissive reflective surface, is reflected by the second transmissive reflective surface, is reflected by the first transmissive reflective surface again, passes through the second transmissive reflective surface and reaches the image plane.

16. The optical system according to claim 1, characterized in that light incident on the optical system from the object side passes through the second transmission reflective surface, is reflected by the first transmission reflective surface, is reflected by the second transmission reflective surface, passes through the first transmission reflective surface, and reaches the image plane.

17. An optical system having a first transmission reflecting surface, a first phase shifter, a second transmission reflecting surface, and a second phase shifter arranged in order, When the radius of curvature of the first transmissive / reflective surface on the optical axis is Rh1, the radius of curvature of the surface on which the first phase shifter is provided is Rr1, and the radius of curvature of the surface on which the second phase shifter is provided is Rr2, |Y / Rh1|≦0.20 |Y / Rr1|≦0.20 |Y / Rr2|≦0.20 An optical system characterized by satisfying the following conditions.

18. An optical system according to any one of claims 1 to 17, An imaging device characterized by having an image sensor that images an object through the optical system.

Images