Optical system and observation device

Abstract

[Problem] To provide an optical system that is capable of appropriately detecting a line-of-sight method of a user while being compact. [Solution] Provided is an optical system (1) that forms an enlarged image of a display surface (PNL) on an exit pupil (EP) and forms a reduced image of the exit pupil on an imaging surface (IM), said optical system (1) comprising a first polarization control means that guides first polarized light in a first direction in a first optical path (RY1) from the display surface to the exit pupil, guides the first polarized light and second polarized light in a second direction, which differs from the first direction, in a second optical path (RY2, RY2a) from the exit pupil to the imaging surface, is disposed in the second optical path, and suppresses the passage of the first polarized light.

Description

Optical system and observation device

[0001] The disclosure herein relates to optical systems and observation devices.

[0002] Observation devices such as head-mounted displays that are worn on the head of an observer (user) and allow the user to view an image are known. Observation devices that have a function of detecting the user's line of sight by providing the observation device with an optical system (imaging optical system) that captures an image of the user's pupils are also known. Patent Document 1 discloses an optical system having an optical path that passes through the optical system that allows the user to view an image and guides an image of the user's pupils or an image reflected by the user's pupils to an imaging element.

[0003] Japanese Patent Application Laid-Open No. 2023-86613

[0004] In the optical system disclosed in Patent Document 1, an optical path that transmits through the transmissive-reflective surface and an optical path that transmits after being reflected twice are simultaneously formed. When the imaging surface is moved closer to the display surface for further miniaturization, the optical path that guides the image displayed on the display surface to the user's eye as an enlarged image overlaps with the optical path that transmits through the transmissive-reflective surface and the optical path that transmits after being reflected twice is guided to the imaging surface. As a result, ghosts and flares caused by the multiple optical paths occur, reducing detection accuracy and making it difficult to properly detect the user's gaze direction.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an optical system that is compact yet capable of appropriately detecting the direction of a user's line of sight.

[0006] An optical system according to one aspect of the present invention is an optical system that forms an enlarged image of a display surface at an exit pupil and forms a reduced image of the exit pupil at an imaging surface, and has a first polarization control means that guides a first polarized light in a first direction in a first optical path from the display surface to the exit pupil, and guides a second polarized light in a second direction different from the first polarized light and the first direction in a second optical path from the exit pupil to the imaging surface, and is arranged in the second optical path to suppress the passage of the first polarized light.

[0007] Other aspects and features of the present invention will be described in the following embodiments.

[0008] It is possible to provide an optical system that is compact yet capable of appropriately detecting the direction of the user's line of sight.

[0009] FIG. 1 is a configuration diagram of an optical system in this embodiment. FIG. 2 is an explanatory diagram of a first optical path in this embodiment. FIG. 3 is a configuration diagram of an optical system in a modified example of this embodiment. FIG. 4 is an explanatory diagram of a mechanism related to the generation of ghosts or flares that occur in the second optical path and the third optical path. FIG. 5 is an explanatory diagram of the second optical path in this embodiment. FIG. 6 is an example of a first polarization control means in this embodiment. FIG. 7 is an explanatory diagram of the third optical path in this embodiment. FIG. 8 is an example of a second polarization control means in this embodiment. FIG. 9 is a detailed diagram of the second lens unit and the third lens unit in this embodiment. FIG. 10 is a schematic diagram of an observation device in this embodiment. FIG. 11 is an explanatory diagram of a display unit of the observation device in this embodiment.

[0010] Hereinafter, embodiments of the optical system disclosed in this specification will be described in detail with reference to the drawings. Note that the drawings may be drawn at a scale different from the actual scale for convenience. In addition, the same reference numerals are used for the same components in the drawings, and duplicated descriptions will be omitted.

[0011] First, an optical system 1 according to this embodiment will be described with reference to FIG. 1 . FIG. 1 is a configuration diagram of the optical system 1. The optical system 1 has a first lens unit (first optical system) LU1 and a second lens unit (second optical system) LU2, and forms an enlarged image of a display surface PNL at an exit pupil EP and a reduced image of the exit pupil on an imaging surface IM. The first lens unit LU1 forms an enlarged image of an image displayed on the display surface PNL at the exit pupil EP of the user's eye EYE (forming an enlarged image of the display surface PNL). The second lens unit LU2 forms an image of the cornea, etc. of the user's eye EYE through the first lens unit LU1 and onto the imaging surface IM. The optical path RY1 from the display surface PNL to the exit pupil EP is referred to as a first optical path, and the optical path RY2 from the eye EYE to the imaging surface IM is referred to as a second optical path. A polarizing unit (circular polarization conversion element) FL is disposed on the optical path RY1 between the display surface PNL and the first lens unit LU1 (on the display surface PNL side of the first transmission-reflection surface HM1). The first lens unit LU1 is rotationally symmetric with respect to the optical axis of the optical path RY1.

[0012] The display surface PNL is the display surface of a display element (spatial modulation element), such as an LCD (Liquid Crystal Display) or an LED (Light Emitting Diode) display. The polarization state can be controlled by the orientation of liquid crystals in a display such as an LCD. In other words, the function of the polarization unit FL may be formed within the display element. In this case, it is not necessary to provide the polarization unit FL between the display surface PNL and the first lens unit LU1.

[0013] The imaging surface IM is the light receiving surface of the imaging element. The imaging element is a photoelectric conversion element such as a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Metal Oxide Semiconductor) sensor. However, this embodiment is not limited to this, and other photoelectric conversion elements such as a SPAD (Single Photon Avalanche Diode) sensor may also be used.

[0014] In the optical system 1, the first lens unit LU1 has a first lens G1 and a second lens G2. The first lens G1 has a first transmission-reflection surface HM1. The second lens G2 has a second transmission-reflection surface HM2. The first lens unit LU1 may include additional lenses as needed to correct various aberrations.

[0015] Next, the optical path (first optical path) RY1 will be described with reference to FIG. 2 . FIG. 2 is an explanatory diagram of the optical path RY1. The polarizing unit FL has a first polarizing element (linear polarizer) PL1 and a first quarter-wave plate QWP1. Light with an axis perpendicular to the transmission axis of the first polarizing element PL1 is preferably absorbed by the first polarizing element PL1. The second transflective surface HM2 has a second quarter-wave plate QWP2 and a polarization-selective reflective polarizing element PBS. The polarization-selective reflective polarizing element PBS is preferably a wire-grid polarizing element. A wire-grid polarizing element is an optical element that has a fine metal grid (slits) and transmits or reflects light depending on its polarization state. The optical path RY1 passes through the first polarizing element PL1 of the polarizing unit FL, and polarized light in one direction (first direction, first polarization direction) is formed. In this embodiment, the first direction is the vertical direction of the paper in FIG. 2 .

[0016] After passing through the first polarizing element PL1, the light is formed into circularly polarized light by the first quarter-wave plate QWP1 and then transmitted through the first transmission-reflection surface HM1. In FIG. 2, the circularly polarized light is formed to be clockwise circularly polarized light relative to the direction of propagation. The light (not shown) reflected by the first transmission-reflection surface HM1 is formed into circularly polarized light counterclockwise relative to the direction of propagation, and is absorbed by the first polarizing element PL1 after passing through the first quarter-wave plate QWP1. The light transmitted through the first transmission-reflection surface HM1 is converted into linearly polarized light by the second quarter-wave plate QWP2 and then enters the polarization-selective reflective polarizing element PBS.

[0017] The polarization-selective reflective polarizing element PBS reflects the linearly polarized light converted by the second quarter-wave plate QWP2 in one direction and transmits the light in the other direction. Therefore, the light transmitted through the first transmission-reflection surface HM1 is reflected once by the polarization-selective reflective polarizing element PBS. The reflected light passes through the second quarter-wave plate QWP2 again, where it is converted into circularly polarized light and reflected by the first transmission-reflection surface HM1.

[0018] The direction of rotation of the circularly polarized light relative to the direction of propagation when it enters the first transmission-reflection surface HM1 is orthogonal to the direction of propagation after it is reflected. Therefore, the polarization state when the light passes through the second quarter-wave plate QWP2 again is orthogonal to the polarization state when it passed through the first time. As a result, the light passes through the polarization-selective reflective polarizing element PBS and reaches the exit pupil EP of the user's eye EYE. Therefore, the optical path RY1 follows an optical path that is reflected twice. This makes it possible to widen the field of view and effectively correct various aberrations while minimizing the thickness of the first lens unit LU1 in the optical axis direction.

[0019] 1, the optical path RY2 passes from the exit pupil EP through the second transmissive-reflective surface HM2 and the first transmissive-reflective surface HM1, and then is imaged on the imaging plane IM by the second lens unit LU2. By not using an optical path that reflects off the first transmissive-reflective surface HM1 and the second transmissive-reflective surface HM2, the number of times the light passes through the transmissive-reflective surfaces can be reduced, thereby suppressing a decrease in the amount of light incident on the imaging plane IM. Furthermore, by passing the light through the first lens unit LU1, the imaging angle of the user's eye EYE can be reduced, and vignetting of the pupil and iris due to factors such as the eyelid and eyeball rotation can be suppressed.

[0020] As shown in FIG. 1, light from the second lens unit LU2 passes through the peripheral portions of the first lens G1 and the second lens G2 that constitute the first lens unit LU1 and then enters the second lens unit LU2. Therefore, it is desirable for the second lens unit LU2 to include an asymmetric optical surface in order to correct decentration aberrations caused by the first lens G1 and the second lens G2. It is also desirable for the imaging surface IM to be parallel to or substantially coplanar with the display surface PNL. This allows the imaging element and display element that constitute the imaging surface IM and the display surface, respectively, to be integrated, thereby making it possible to reduce the size of the entire device.

[0021] 1, the first transmission-reflection surface HM1 and the second transmission-reflection surface HM2 are formed on the refractive surfaces of the first lens G1 and the second lens G2, respectively, but this embodiment is not limited to this. For example, the first transmission-reflection surface HM1 and the second transmission-reflection surface HM2 may be disposed on both surfaces of the first lens G1. Alternatively, a cover glass or the like may be disposed, and the transmission-reflection surfaces may be formed on the cover glass or the like.

[0022] Furthermore, the optical path is not limited to that shown in FIG. 2 , and the transmission axis of the polarizing element and the slow axis of the quarter-wave plate may be changed as appropriate. Furthermore, the polarization-selective reflective polarizing element PBS shown in FIG. 2 transmits or reflects linearly polarized light, but is not limited thereto. It may also be an element that transmits or reflects circularly polarized light depending on the direction of rotation. The transmission-reflection surface may also be an element that transmits or reflects linearly polarized light or circularly polarized light depending on the direction. In this case, the quarter-wave plate must be appropriately positioned, but appropriate modifications or changes can be made within the scope of the present embodiment. Here, the polarization-selective reflective polarizing element and the polarizing element transmit 80% or more of incident light polarized parallel to the transmission axis. They transmit 5% or less of incident light polarized perpendicular to the transmission axis.

[0023] Next, an optical system 1a as a modified example of this embodiment will be described with reference to Fig. 3. Fig. 3 is a configuration diagram of the optical system 1a. In addition to a first lens unit LU1 and a second lens unit LU2, the optical system 1a has a third lens unit (third optical system) LU3 that forms an optical path (third optical path) RY3 for guiding light emitted by a light-emitting surface LS of a light-emitting element (light source) to the user's eye EYE.

[0024] In the optical path RY3, the light from the light-emitting surface LS passes through the third lens unit LU3, and then passes through the first transmission-reflection surface HM1 of the first lens G1 and the second transmission-reflection surface HM2 of the second lens G2, illuminating the user's eye EYE. By passing the light through the third lens unit LU3, it is possible to make the unit size more compact than when the light-emitting surface is located outside the outer diameter of the lens (for example, the first lens unit LU1).

[0025] The light-emitting surface LS illuminates the user's eye EYE, and the light diffused by the eye EYE or the light reflected by the cornea is guided (directed) to the imaging plane IM by the first lens unit LU1 and the second lens unit LU2. While only one light-emitting surface LS is shown in FIG. 3 , light-emitting surfaces LS (multiple light sources) may be arranged at multiple positions to prevent vignetting of light reflected by the cornea of ​​the eye EYE due to factors such as the eyelid or eyeball rotation. In this case, it is desirable to position the third lens unit LU3 so that it corresponds to the multiple light-emitting surfaces LS. Furthermore, it is desirable that the light emitted by the light-emitting surface LS or the light guided to the imaging plane IM be near-infrared light (wavelength 750 to 1000 nm).

[0026] The third lens unit LU3 preferably includes an asymmetric optical surface to properly illuminate the eye EYE, which allows the orientation angle of the light-emitting surface LS to be constant regardless of the first lens unit LU1, thereby making it possible to reduce manufacturing costs, etc.

[0027] Next, the mechanism of occurrence of ghost or flare caused by the optical paths RY2 and RY3 of the optical system 1a will be described with reference to Fig. 4. Fig. 4 is an explanatory diagram of the mechanism of occurrence of ghost or flare.

[0028] The optical system 1a has an optical path RY2a that is guided to the imaging plane IM and is different from the optical path RY2, and an optical path RY3a that is guided from the light-emitting surface LS to the eye EYE and is different from the optical path RY3. That is, the second optical path includes the optical path (single-path optical path) RY2 and the optical path (triple-path optical path) RY2a, and the third optical path includes the optical path RY3 and the optical path RY3a. The light along the optical path RY2a is reflected by each of the first and second transmission-reflection surfaces HM1 and HM2, then passes through the first transmission-reflection surface HM1 and is guided to the second lens unit LU2. The light along the optical path RY3a is reflected by each of the first and second transmission-reflection surfaces HM1 and HM2, then passes through the second transmission-reflection surface HM2 and is guided to the exit pupil EP.

[0029] Next, the optical path RY2 and the optical path RY2a will be described with reference to Fig. 5. Fig. 5 is an explanatory diagram of the optical path RY2 and the optical path RY2a. Light from the eye EYE passes through the polarization-selective reflective polarizing element PBS and the second quarter-wave plate QWP2 that constitute the second transmission-reflection surface HM2, and is incident on the first transmission-reflection surface HM1 as circularly polarized light. One light is transmitted by the first transmission-reflection surface HM1, and the other light is reflected and separated. The optical path of the transmitted light is the optical path RY2, and the optical path of the reflected light is the optical path RY2a.

[0030] The light that passes through the first transmission-reflection surface HM1 is guided directly to the imaging surface IM, and the light that reflects off the second transmission-reflection surface HM2 is polarized in the opposite direction to the direction of propagation, different from the polarization state at the time of incidence, and passes through the second quarter-wave plate QWP2 again. The light that is reflected by the polarization-selective reflective polarizing element PBS, passes through the second quarter-wave plate QWP2, and passes through the first transmission-reflection surface HM1 is guided to the imaging surface IM. The polarization state (polarization direction, second direction) RP11 of the optical path RY2 guided to the imaging surface IM is orthogonal to the polarization state (polarization direction, first direction) RP12 of the optical path RY2a. Furthermore, the polarization state RP11 after passing through the polarizing unit FL in FIG. 2 is orthogonal to the polarization state RP11. In other words, the polarization states for forming the optical paths that reflect off the first transmission-reflection surface HM1 and the second transmission-reflection surface HM2 are orthogonal to the polarization state RP11.

[0031] Therefore, a first polarization control means is disposed between the first transmissive-reflective surface HM1 and the imaging surface IM to prevent light in polarization state RP12 (first polarization) from reaching the imaging surface IM (to reduce the amount of light in polarization state RP12 passing through the optical path RY2a). This prevents the optical paths RY2 and RY2a from intermingling, and allows the light in optical path RY2 (second polarization) to be guided to the imaging surface IM (to prevent the light in optical path RY2a from reaching the imaging surface IM). Preferably, the amount of light in optical path RY2a that reaches the imaging surface IM is 5% or less of the light in optical path RY2. More preferably, only the light in optical path RY2 reaches the imaging surface IM.

[0032] Next, an example of the first polarization control means on the optical path RY2 will be described with reference to Fig. 6. Fig. 6 shows an example of the first polarization control means on the optical path RY2. In this embodiment, the first polarization control means has a third quarter-wave plate QWP3 and a second polarizing element PL2.

[0033] As in FIG. 5 , the light along optical paths RY2 and RY2a transmitted through the first transmission-reflection surface HM1 enters the third quarter-wave plate QWP3 and the second polarizing element PL2, which constitute the first polarization control means. The third quarter-wave plate QWP3 in FIG. 6 and the first quarter-wave plate QWP1 in FIG. 2 have the same slow axis. The transmission axis of the second polarizing element PL2 and the transmission axis of the first polarizing element PL1 in FIG. 2 are orthogonal to each other. The polarization states of the light along optical path RY2 and the light along optical path RY2a are orthogonal to each other. Therefore, the second polarizing element PL2 guides only the light along optical path RY2 to the imaging plane IM.

[0034] 6, the second polarizing element PL2 is configured to allow only light of the optical path RY2 to pass through, but this is not limiting. The transmission axes of the first polarizing element PL1 and the second polarizing element PL2 may be aligned with each other, and the slow axis of the first quarter-wave plate QWP1 and the slow axis of the third quarter-wave plate QWP3 may be orthogonal to each other.

[0035] Although the polarization states RP11 and RP12 are orthogonal to each other, the polarization states may not be strictly orthogonal due to manufacturing errors, etc. In this case, it is preferable that the transmission axis or slow axis of the first polarization control means is set within a range of 70° to 110° relative to the transmission axis or slow axis of the polarizing unit FL in FIG. 2 . By keeping it within this range, ghosts and flares can be suppressed, and the accuracy of detecting the user's line of sight direction by the imaging surface IM can be improved. More preferably, the transmission axis or slow axis of the first polarization control means is set within a range of 75° to 105° relative to the transmission axis or slow axis of the polarizing unit FL.

[0036] Next, the optical paths RY3 and RY3a will be described with reference to FIG. 7. FIG. 7 is an explanatory diagram of the optical paths RY3 and RY3a. Light from the light-emitting surface LS passes through the first transmission-reflection surface HM1 and the second quarter-wave plate QWP2 and enters the polarization-selective reflective polarizing element PBS. The polarization-selective reflective polarizing element PBS separates the light into transmitted light and reflected light. The transmitted light proceeds directly to the eye EYE, while the reflected light passes again through the quarter-wave plate QWP2 to become circularly polarized light and is reflected by the first transmission-reflection surface HM1. The reflected light passes through the quarter-wave plate QWP2 and the polarization-selective reflective polarizing element PBS and enters the eye EYE.

[0037] 4, the optical path RY3 and the optical path RY3a pass through the peripheral portion of the first lens unit LU1 before reaching the eye EYE, and therefore the optical path RY3 and the optical path RY3a reach different points on the cornea of ​​the eye EYE. Therefore, two reflected images of the cornea captured by the imaging surface IM are formed, reducing detection accuracy and making it difficult to properly detect the user's gaze direction. Furthermore, by using the optical path RY3 instead of the optical path RY3a, it is possible to suppress a reduction in the amount of light caused by the first transmissive-reflective surface HM1.

[0038] Next, an example of the second polarization control means on the optical path RY3 will be described with reference to Fig. 8. Fig. 8 shows an example of the second polarization control means. The second polarization control means has a third polarizing element PL3 ​​and a fourth quarter-wave plate QWP4. The second polarization control means transmits only polarized light that is transmitted by the polarization-selective reflective polarizing element PBS from the light emitting surface LS.

[0039] 8, light from the light-emitting surface LS passes through the third polarization element PL3, which is the second polarization control means, and the fourth quarter-wave plate QWP4, and then passes through the first transmission-reflection surface HM1 and the second quarter-wave plate QWP2 in a circularly polarized state, and enters the polarization-selective reflective polarizing element PBS. Because the polarization state is selected by the third polarization element PL3, the light is only transmitted through the polarization-selective reflective polarizing element PBS and is irradiated onto the eye EYE.

[0040] The transmission axis of the third polarizing element PL3 ​​in Fig. 8 is orthogonal to the transmission axis of the first polarizing element PL1 in Fig. 2 and parallel to the transmission axis of the second polarizing element PL2 in Fig. 6. As a result, light emitted from the light-emitting surface LS can be guided to the eye EYE without being reflected by the polarization-selective reflective polarizing element PBS, thereby achieving high detection accuracy and enabling the user's gaze direction to be detected appropriately. The transmission axes of the first to third polarizing elements PL1, PL2, and PL3 may be aligned with each other, and the slow axis of the fourth quarter-wave plate QWP4 and the slow axis of the first quarter-wave plate QWP1 may be orthogonal to each other and parallel to the slow axis of the third quarter-wave plate QWP3.

[0041] As with the first polarization control means described with reference to Fig. 6, the transmission axis or slow axis of the second polarization control means is preferably set within a range of 70° to 110° relative to the transmission axis or slow axis of the polarizing unit FL in Fig. 2. More preferably, the transmission axis or slow axis of the second polarization control means is set within a range of 75° to 105° relative to the transmission axis or slow axis of the polarizing unit FL.

[0042] Next, the second lens unit LU2 and the third lens unit LU3 will be described in detail with reference to FIG. 9 . FIG. 9 is a detailed diagram of the second lens unit LU2 and the third lens unit LU3. The second lens unit LU2 includes optical elements G21 and G22, an aperture stop (aperture stop) AP21, a third quarter-wave plate QWP3, a near-infrared transmission filter IRF, and a second polarizing element PL2. The third lens unit LU3 includes an optical element G31, an aperture stop (aperture stop) AP31, a fourth quarter-wave plate QWP4, and a third polarizing element PL3. The optical elements G21, G22, and G31 have functions such as refraction, reflection, and diffraction. It is preferable that the second lens unit LU2 has at least a diffractive surface. Furthermore, at least one of the optical elements G21, G22, and G31 may be configured as a lens (metalens) having a metasurface. In this case, the metasurface may include polarization control means such as a quarter-wave plate and a polarizing element, i.e., the metasurface may constitute at least one of the first polarization control means or the second polarization control means.

[0043] The first, third, and fourth quarter-wave plates QWP1, QWP3, and the first, second, and third polarizing elements PL1, PL2, and PL3 are each composed of separate members. However, this embodiment is not limited to this, and they may be composed of the same member if their slow axes or transmission axes are aligned. Furthermore, the number of optical elements, the position of the aperture, and the like are not limited to the configuration shown in Figure 9, and may be modified or changed as appropriate.

[0044] Next, an observation device 100 including the optical system 1 of this embodiment will be described with reference to Fig. 10 and Fig. 11. Fig. 10 is a schematic diagram of the observation device 100. Fig. 11 is an explanatory diagram of the display units 102, 202 of the observation device 100.

[0045] As shown in Fig. 10, the observation device 100 has optical systems 101, 201 and display units 102, 202. As shown in Fig. 11, the display units 102, 202 each include a display element PE, an image sensor SE, and a light-emitting element LE. The display element PE, the image sensor SE, and the light-emitting element LE may be formed on a single panel surface, or may be configured as separate members.

[0046] 10 , the observation device 100 allows the user to view an image displayed by the display unit 102 as an enlarged image on the right eye side of the user through the optical system 101, and allows the user to view an image displayed by the display unit 202 as an enlarged image on the left eye side of the user through the optical system 201. The display unit or optical system may be different for each side depending on the user's eyesight, etc. As shown in FIG. 11 , the image sensor SE is disposed in one location and the light-emitting elements LE are disposed in four locations, but this embodiment is not limited to this, and the positions, numbers, or sizes of the image sensor SE or the light-emitting elements LE can be modified or changed as appropriate.

[0047] The image of the user's pupil or the image reflected from the cornea acquired by the image sensor SE is converted into a line-of-sight direction by a calculation unit 301 built into the observation device 100 or provided in an external device connected to the observation device 100. Depending on the line-of-sight direction, the resolution of the image displayed on the display unit 102, 202 can be changed, or a user interface on the display (not shown) can be processed. Alternatively, the image of the user's iris can be used as an authentication means for identifying the user. Furthermore, the image of the pupil or the image reflected from the cornea or the iris image may be acquired from only one eye.

[0048] The optical system of this embodiment has an optical path (first optical path) RY1 and optical paths (second optical paths) RY2 and RY2a. In the optical path RY1, polarized light in a first direction (first polarized light) is guided from the display surface PNL toward the exit pupil EP. In the optical paths RY2 and RY2a, polarized light in the first direction and polarized light in a second direction (second polarized light) different from the first direction are guided from the exit pupil EP toward the imaging surface IM. The optical system has a first polarization control means that suppresses the passage of polarized light in the first direction in the second optical path (suppresses polarized light in the first direction from reaching the imaging surface IM). Note that the polarized light in the first direction and the polarized light in the second direction each correspond to the polarization direction (polarization axis direction, vibration direction) of the light, not the direction of travel of the light.

[0049] Preferably, the optical system has a first transmission-reflection surface HM1 and a second transmission-reflection surface HM2, and a polarization-selective reflective polarizing element PBS is provided on at least one of the first transmission-reflection surface HM1 or the second transmission-reflection surface HM2. The first polarization control means is disposed between the first transmission-reflection surface HM1 and the imaging surface IM. Preferably, the first polarization control means has a second polarizing element PL2.

[0050] In the above-described embodiment, in order to prevent triple-path light from reaching the imaging plane IM, the second lens unit LU2, which has the function of preventing triple-path light from reaching the imaging plane IM, is disposed between the first lens unit LU1 and the imaging plane IM. That is, in the above-described embodiment, a configuration in which the second lens unit LU2 is provided with a first polarization control means has been described. However, the present embodiment is not limited to this.

[0051] Instead of providing the second lens unit LU2, the first lens unit LU1 may be configured to have the same function as described above. That is, the first lens unit LU1 may be provided with a first polarization control means. As the first polarization control means, for example, an optical filter (optical element) that prevents triple-path light from exiting the first lens unit LU1 (from entering the second lens unit LU2) may be provided inside the first lens unit LU1. Such an optical filter controls the polarization state of light in a specific wavelength range. For example, an optical filter that functions with near-infrared light (wavelengths 750 to 1550 nm) as light in the specific wavelength range (an optical filter that controls the polarization state of near-infrared light) may be used. This allows the filter function to be exerted on the light in the second optical path (near-infrared light) that is guided from the exit pupil EP to the imaging surface IM without affecting the light in the first optical path (visible light) that is guided from the display surface PNL to the exit pupil EP. By using such an optical filter, it is possible to prevent light in the triple-pass polarization direction (second direction) in the second optical path from exiting the first lens unit LU1. The optical filter is disposed, for example, closer to the exit pupil EP than the first transmission-reflection surface HM1. The optical filter is disposed on the surface of at least one lens (optical element) constituting the first lens unit LU1, or is disposed as an independent optical element.

[0052] Alternatively, instead of providing the second lens unit LU2, the image sensor SE may be configured to have the same functionality as described above. That is, the image sensor SE may be provided with a first polarization control means. As the first polarization control means, for example, a polarizing element that passes only light of a desired polarization state (polarization direction) (and does not pass light of the triple-pass polarization direction) may be provided at a position corresponding to each color filter of the image sensor SE. By using an image sensor SE (polarized image sensor) equipped with such a polarizing element, it is possible to prevent light of the triple-pass polarization direction (second direction) that has exited the first lens unit LU1 from entering the imaging plane IM.

[0053] The optical system of this embodiment can suppress ghosts or flares caused by different optical paths and improve the accuracy of detecting the user's gaze direction. Therefore, this embodiment can provide an optical system and observation device that are compact yet capable of appropriately detecting the user's gaze direction.

[0054] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the gist of the present invention.

Claims

1. An optical system that forms an enlarged image of a display surface at an exit pupil and forms a reduced image of the exit pupil on an imaging surface, the optical system comprising: a first optical path from the display surface to the exit pupil that guides a first polarized light in a first direction; a second optical path from the exit pupil to the imaging surface that guides a second polarized light in a second direction different from the first polarized light and the first direction; and a first polarization control means disposed on the second optical path that suppresses the passage of the first polarized light.

2. The optical system according to claim 1, characterized in that the optical system has a first transmissive-reflective surface and a second transmissive-reflective surface, a polarization-selective reflective polarizing element is provided on at least one of the first transmissive-reflective surface or the second transmissive-reflective surface, and the first polarization control means is disposed between the first transmissive-reflective surface and the imaging surface.

3. The optical system according to claim 2, wherein said first polarization control means comprises a polarizing element.

4. The optical system according to claim 1, characterized in that the optical system has a first transmissive-reflective surface and a second transmissive-reflective surface, a polarization-selective reflective polarizing element is provided on at least one of the first transmissive-reflective surface or the second transmissive-reflective surface, and the first polarization control means is arranged on the side of the exit pupil relative to the first transmissive-reflective surface.

5. The optical system according to claim 4, wherein the first polarization control means is an optical filter that controls the polarization state of near-infrared light.

6. An optical system according to any one of claims 2 to 5, characterized in that light on the first optical path passes from the display surface, passes through the first transmissive-reflective surface, reflects off the second transmissive-reflective surface, reflects off the first transmissive-reflective surface, passes through the second transmissive-reflective surface, and is guided to the exit pupil.

7. An optical system according to any one of claims 2 to 6, characterized in that the light in the second optical path passes from the exit pupil, passes through the second transmissive-reflective surface, passes through the first transmissive-reflective surface, and is directed to the imaging surface.

8. The optical system according to any one of claims 2 to 7, characterized in that the second transmissive-reflective surface is provided on the polarization-selective reflective polarizing element.

9. The optical system according to any one of claims 2 to 8, characterized in that the optical system has a circular polarization conversion element disposed on the display surface side of the first transmissive-reflective surface.

10. The optical system according to claim 9, wherein said circular polarization conversion element comprises a linear polarizer and a quarter-wave plate.

11. The optical system according to any one of claims 2 to 10, wherein the polarization-selective reflective polarizing element is a wire grid polarizing element.

12. An optical system described in any one of claims 1 to 11, characterized in that the first polarization control means transmits light having a polarization direction within a range of 70° to 110° with respect to the polarization direction of light incident on the first optical path from the display surface to the optical system.

13. An optical system according to any one of claims 1 to 12, characterized in that the optical system has a first optical system that forms the first optical path, and the first optical system is rotationally symmetric with respect to the optical axis of the first optical path.

14. The optical system according to claim 13, characterized in that the optical system has a second optical system that forms the second optical path together with the first optical system, and the second optical system is disposed between the first optical system and the imaging surface.

15. The optical system described in claim 13 or 14, characterized in that the optical system has a third optical path that passes from the light-emitting surface through the optical system and is led to the exit pupil, the optical system has a third optical system that forms the third optical path together with the first optical system, the third optical system is arranged between the light-emitting surface and the first optical system, and has a second polarization control means.

16. The optical system described in claim 15, characterized in that the optical system has a first transmissive-reflective surface and a second transmissive-reflective surface, at least one of the first transmissive-reflective surface or the second transmissive-reflective surface is provided with a polarization-selective reflective polarizing element, and light in the third optical path passes through the first transmissive-reflective surface, passes through the second transmissive-reflective surface, and is guided to the exit pupil.

17. The optical system according to claim 16, wherein the second polarization control means transmits polarized light that is transmitted by the polarization-selective reflective polarizing element, out of the light from the light-emitting surface.

18. The optical system according to any one of claims 15 to 17, wherein the transmission axis of said first polarization control means and the transmission axis of said second polarization control means are parallel to each other.

19. The optical system according to claim 14, wherein the second optical system has a diffractive surface.

20. The optical system of claim 14, wherein the second optical system comprises a metasurface.

21. The optical system of claim 20, wherein the metasurface functions as the first polarization control means.

22. An observation device comprising the optical system according to any one of claims 1 to 21, a display element having the display surface, and an imaging element having the imaging surface.

23. The observation device of claim 22, further comprising a plurality of light sources each having a light-emitting surface.

24. An observation device having an optical system that forms an enlarged image of a display surface at an exit pupil and forms a reduced image of the exit pupil on an imaging surface, and an imaging element equipped with the imaging surface, wherein a first polarized light in a first direction is guided in a first optical path from the display surface to the exit pupil, and a second polarized light in a second direction different from the first polarized light and the first direction is guided in a second optical path from the exit pupil to the imaging surface, and the imaging element is arranged in the second optical path and has first polarization control means that suppresses the passage of the first polarized light.

25. The optical system according to claim 24, wherein said first polarization control means comprises a polarizing element.

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