Retinal projection device

Abstract

The retina projection device is provided with: a projector module including a laser module that emits laser light, a collimator lens that converts the laser light into parallel light beams, and a movable mirror for scanning with the light beams; a projection lens that focuses the light beam emitted from the projector module at a focusing position; an optical unit that is disposed so as to overlap the focus position and includes a deflecting element that changes the traveling direction of the light beam; an optical device which converts the light beam into parallel light and irradiates the retina of the user; and a controller that adjusts a traveling direction of the light beam based on the deflecting element in accordance with a position of the pupil of the user.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application is based on Japanese Patent Application No. 2023-138955, filed on August 29, 2023, and claims the benefit of priority thereto, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The invention relates to a retinal projection device. Background Art

[0004] A retinal projection device that directly projects an image onto the user's retina is known (for example, refer to U.S. Patent Application Publication No. 2019 / 0361250, Japanese Patent Application Publication No. 2021-5072, and International Publication No. 2019 / 146367). Summary of the invention

[0005] In the retinal projection device described in U.S. Patent Application Publication No. 2019 / 0361250, Japanese Patent Publication No. 2021-5072, and International Publication No. 2019 / 146367, when the user moves his eyes, the image may not be correctly recognized. In the technical field, it is desirable to expand the movable range of the eye (eye box) that can correctly recognize the entire image.

[0006] The present invention describes a retinal projection device capable of expanding the eye box.

[0007] A retinal projection device according to one aspect of the present invention comprises: a projector module, which includes a laser module that emits laser light, a collimating lens that converts the laser light into a parallel light beam, and a movable mirror for performing light beam-based scanning; a projection lens that focuses the light beam emitted from the projector module at a focusing position; an optical unit that is configured to overlap with the focusing position and includes a deflection element that changes the direction of travel of the light beam; an optical device that converts the light beam into parallel light and irradiates the light beam to the user's retina; and a controller that adjusts the direction of travel of the light beam based on the deflection element according to the position of the user's pupil.

[0008] In the retinal projection device, an optical unit including a deflection element is configured to overlap with the focus position, and the traveling direction of the light beam based on the deflection element is adjusted according to the position of the user's pupil. According to this structure, even if the user moves his eyes, the traveling direction of the light beam can be changed to follow the movement of the user's pupil. Because the deflection element is configured near the focus position, the spherical aberration caused by changing the traveling direction (deflection) of the light beam is reduced. Therefore, the quality of the image on the retina is maintained, so the user can correctly recognize the image. As a result, the eye box can be expanded.

[0009] In some embodiments, the retinal projection device may also include a first wavelength plate, which is disposed between the laser module and the deflection element to convert linear polarized light into circularly polarized light. The deflection element may also include: one or more second wavelength plates, which can switch between a state of preserving the polarization state of circularly polarized light and a state of converting the circularly polarized light into circularly polarized light of opposite polarity according to an applied voltage; one or more Pancharatnam-Berry phase optical elements, which convert the circularly polarized light into circularly polarized light of opposite polarity and diffract the circularly polarized light along a diffraction direction corresponding to the polarity of the incident circularly polarized light. One or more second wavelength plates and one or more Pancharatnam-Berry phase optical elements may also be arranged alternately one by one to form an arrangement body. According to this structure, by switching the second wavelength plate between a state of preserving the polarization state of circularly polarized light and a state of converting the circularly polarized light into circularly polarized light of opposite polarity, the polarity (polarization state) of the circularly polarized light passing through the second wavelength plate can be switched. The diffraction direction of the Pancharatnam-Berry phase optical element provided at the subsequent stage of the second wave plate is determined by the polarity of the circularly polarized light. Therefore, the traveling direction of the light beam can be changed by the voltage applied to the second wave plate.

[0010] In some embodiments, the deflection element may also include a reflector that reflects the circularly polarized light while preserving the polarity of the circularly polarized light. The reflector may also be disposed at one end of the array body. In this case, the light beam that has passed through the array body is reflected by the reflector and passes through the array body. Therefore, the number of directions of travel that can be changed by the deflection element can be increased.

[0011] In several embodiments, one or more Pancharatnam-Berry phase optical elements may also be formed from liquid crystal polymers or metasurfaces. By using liquid crystal polymers or metasurfaces, Pancharatnam-Berry phase optical elements can be easily formed.

[0012] In some embodiments, the second wavelength plate may also include a pair of transparent electrodes and a liquid crystal layer disposed between the pair of transparent electrodes. In this case, by applying a voltage between the pair of transparent electrodes, an electric field is generated in the liquid crystal layer, and the liquid crystal molecules contained in the liquid crystal layer are oriented along the direction of the electric field. Therefore, in a state where a voltage is applied between the pair of transparent electrodes, the second wavelength plate preserves the polarization state of the circularly polarized light passing through the second wavelength plate. In a state where no voltage is applied between the pair of transparent electrodes, the liquid crystal molecules contained in the liquid crystal layer are in an in-plane oriented state. At this time, the second wavelength plate converts the circularly polarized light passing through the second wavelength plate into circularly polarized light of the opposite polarity. In this way, it is possible to switch between a state of preserving the polarization state of the circularly polarized light and a state of converting the circularly polarized light into circularly polarized light of the opposite polarity, depending on the presence or absence of a voltage applied between the pair of transparent electrodes.

[0013] In some embodiments, the retinal projection device may further include a wavefront correction unit that corrects the aberration of the wavefront of the light beam that passes through the pupil among the light beams constituting the light beam. In this case, the resolution at the center of the field of view can be improved.

[0014] In some embodiments, the wavefront correction unit may be formed by any one of LCOS, a liquid crystal lens, and a deformable mirror. By using any one of these devices, the wavefront correction unit can be easily realized.

[0015] In some embodiments, the retinal projection device may also include a focusing unit, which is arranged between the optical unit and the optical device to focus the light beam. In this case, the optical unit can be arranged at a position separated from the optical device. Therefore, the degree of freedom of the configuration of the optical unit can be increased.

[0016] In some embodiments, the laser module may emit laser light obtained by combining red laser light having a red wavelength, green laser light having a green wavelength, and blue laser light having a blue wavelength. In this case, a full-color retinal projection device can be realized.

[0017] In some embodiments, the retinal projection device may also include a filter that allows circularly polarized light of a first polarity in red wavelength light to pass through and reflects circularly polarized light of a second polarity different from the first polarity, allows circularly polarized light of a second polarity in green wavelength light to pass through and reflects circularly polarized light of the first polarity, and allows circularly polarized light of a first polarity in blue wavelength light to pass through and reflect circularly polarized light of the second polarity. The optical device may also be a holographic combiner. The optical device may also include: a first holographic diffraction layer that diffracts circularly polarized light of a first polarity in a first wavelength range including red wavelengths; a second holographic diffraction layer that diffracts circularly polarized light of a second polarity in a second wavelength range including green wavelengths; and a third holographic diffraction layer that diffracts circularly polarized light of a first polarity in a third wavelength range including blue wavelengths.

[0018] In order to expand the eye box, it is necessary to expand the allowable range of the incident angle of the light beam incident on the holographic combiner. If a broadband element with a large allowable range of the incident angle is used, the allowable range of wavelength is expanded. In this case, stray light caused by chromatic aberration may be generated. In contrast, the circularly polarized light of the first polarity in the red wavelength light is extracted through the filter, the circularly polarized light of the second polarity in the green wavelength light is extracted, and the circularly polarized light of the first polarity in the blue wavelength light is extracted. Because the first holographic diffraction layer diffracts the circularly polarized light of the first polarity, even if the allowable range of the wavelength of the first holographic diffraction layer is expanded, the circularly polarized light of the second polarity with the green wavelength is not easily diffracted. Similarly, because the second holographic diffraction layer diffracts the circularly polarized light of the second polarity, even if the allowable range of the wavelength of the second holographic diffraction layer is expanded, the circularly polarized light of the first polarity with the red wavelength and the circularly polarized light of the first polarity with the blue wavelength are not easily diffracted. Likewise, since the third hologram diffraction layer diffracts the circularly polarized light of the first polarity, the circularly polarized light of the second polarity having a green wavelength is not easily diffracted even if the permissible wavelength range of the third hologram diffraction layer is expanded, thereby reducing the possibility of stray light caused by chromatic aberration.

[0019] In some embodiments, the first holographic diffraction layer may also be composed of a cholesteric liquid crystal polymer layer having a spiral structure, the spiral structure having a spiral pitch corresponding to a red wavelength and twisted in a twisting direction reflecting circularly polarized light of a first polarity. The second holographic diffraction layer may also be composed of a cholesteric liquid crystal polymer layer having a spiral structure, the spiral structure having a spiral pitch corresponding to a green wavelength and twisted in a twisting direction reflecting circularly polarized light of a second polarity. The third holographic diffraction layer may also be composed of a cholesteric liquid crystal polymer layer having a spiral structure, the spiral structure having a spiral pitch corresponding to a blue wavelength and twisted in a twisting direction reflecting circularly polarized light of a first polarity.

[0020] If the torsion direction of the torsion structure of the electric field vector generated by the rotation of the electric field vector of the circularly polarized light at a certain moment and with the traveling direction of the light as the axis is consistent with the torsion direction of the torsion structure of the orientation direction of the liquid crystal molecules of the cholesteric liquid crystal polymer layer, and the incident light satisfies a certain condition, Bragg reflection is caused and the incident light is diffracted and reflected. On the other hand, if the above-mentioned torsion directions are opposite to each other, Bragg reflection is not caused and the incident light is transmitted. The first holographic diffraction layer is configured to reflect circularly polarized light of the first polarity of the red wavelength, the second holographic diffraction layer is configured to reflect circularly polarized light of the second polarity of the green wavelength, and the third holographic diffraction layer is configured to reflect circularly polarized light of the first polarity of the blue wavelength. Therefore, the above-mentioned function of the optical unit can be realized.

[0021] In some embodiments, the filter may also include: a first filter layer, which is composed of a first cholesteric liquid crystal polymer layer having a spiral structure, wherein the spiral structure has a spiral pitch corresponding to the red wavelength and is twisted in a twisting direction that reflects the circularly polarized light of the second polarity; a second filter layer, which is composed of a second cholesteric liquid crystal polymer layer having a spiral structure, wherein the spiral structure has a spiral pitch corresponding to the green wavelength and is twisted in a twisting direction that reflects the circularly polarized light of the first polarity; and a third filter layer, which is composed of a third cholesteric liquid crystal polymer layer having a spiral structure, wherein the spiral structure has a spiral pitch corresponding to the blue wavelength and is twisted in a twisting direction that reflects the circularly polarized light of the second polarity.

[0022] If the torsion direction of the torsion structure of the electric field vector generated by the rotation of the electric field vector of the circularly polarized light at a certain moment and with the direction of travel of the light as the axis is consistent with the torsion direction of the torsion structure of the orientation direction of the liquid crystal molecules of the cholesteric liquid crystal polymer layer, and the incident light satisfies a certain condition, Bragg reflection is caused and the incident light is diffracted and reflected. On the other hand, if the above-mentioned torsion directions are opposite to each other, Bragg reflection is not caused and the incident light is transmitted. The first filter layer is configured to reflect circularly polarized light of the second polarity from light of a red wavelength, the second filter layer is configured to reflect circularly polarized light of the first polarity from light of a green wavelength, and the third filter layer is configured to reflect circularly polarized light of the second polarity from light of a blue wavelength. Therefore, circularly polarized light of the first polarity of a red wavelength, circularly polarized light of the second polarity of a green wavelength, and circularly polarized light of the first polarity of a blue wavelength can be extracted, and the above-mentioned function of the filter can be realized.

[0023] According to various aspects and embodiments of the present invention, the eye box can be expanded. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a diagram showing a basic structure of a retinal projection device according to one embodiment.

[0025] Figure 2 It is a rough representation Figure 1 A diagram of the structure of the deflection element is shown.

[0026] Figure 3 It is a rough representation Figure 2 Figure 2 shows the structure of the wave plate.

[0027] Figure 4 It is a rough representation Figure 2 Figure 2 shows the structure of the Pancharatnam-Berry phase optical element.

[0028] Figure 5 It is along Figure 4 Cross-sectional view of the V-V line.

[0029] Figure 6 It is used for Figure 2 A diagram illustrating the operation of the deflection element shown.

[0030] Figure 7 It is used for Figure 2 A diagram illustrating the operation of the deflection element shown.

[0031] Figure 8 It is used for Figure 2 A diagram illustrating the operation of the deflection element shown.

[0032] Fig. 9 It is used for Figure 2 A diagram illustrating the operation of the deflection element shown.

[0033] Fig.10 This is a diagram for explaining the change in the wave number vector due to deflection.

[0034] Fig.11 This is a diagram for explaining the case where the focus position differs depending on the axial direction.

[0035] Fig.12 It is a diagram showing a basic structure of a retinal projection device according to a modified example.

[0036] Fig.13 Yes means Figure 1 FIG. 1 is a diagram showing an application example of a retinal projection device.

[0037] Fig.14 Yes means Figure 1 FIG. 5 is a diagram showing another application example of the retinal projection device.

[0038] Fig.15 Yes means Figure 1 A diagram of yet another application example of the retinal projection device shown.

[0039] Fig.16 Yes means Figure 1 A diagram of yet another application example of the retinal projection device shown.

[0040] Fig.17 It is a rough representation Fig.16 A diagram of the structure of the deflection element is shown.

[0041] Fig.18 It is used for Fig.16 A diagram illustrating the operation of the deflection element shown.

[0042] Fig.19 Yes means Figure 1 A diagram of yet another application example of the retinal projection device shown.

[0043] Fig. 20 It is a rough representation Fig.19 Figure 2 shows the structure of the notch filter.

[0044] Fig.21 It is used for Fig.19 The diagram shows the principle of the notch filter.

[0045] Fig. 22 It is used for Fig.19 The diagram shows the principle of the notch filter.

[0046] Fig.23 It is used for Fig.19 A diagram illustrating the principle of a reflector shown.

[0047] Fig.24 It is used for Fig.19 A diagram illustrating the principle of a reflector shown. DETAILED DESCRIPTION

[0048] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, the same elements are marked with the same symbols in the description of the accompanying drawings, and repeated descriptions are omitted. In each figure, an XYZ coordinate system is sometimes shown. The Y-axis direction is a direction that intersects (e.g., is orthogonal to) the X-axis direction and the Z-axis direction. The Z-axis direction is a direction that intersects (e.g., is orthogonal to) the X-axis direction and the Y-axis direction.

[0049] Reference Figure 1 , a retinal projection device according to one embodiment is described. Figure 1 This is a diagram showing a basic structure of a retinal projection device according to one embodiment. Figure 1 The retinal projection device 1 shown is a device that directly projects (draws) an image onto the user's retina. The retinal projection device 1 is, for example, mounted on a near-eye wearable device. Examples of near-eye wearable devices include smart glasses such as AR (Augmented Reality) glasses, VR (Virtual Reality) glasses, and MR (Mixed Reality) glasses. The retinal projection device 1 includes a projector module 2, a projection lens 3, an optical unit 4, an optical device 5, and a controller 10.

[0050] The projector module 2 is a module that performs scanning using a light beam. The projector module 2 includes a laser module 21, a collimator lens 22, a movable mirror 23, and a wavelength plate 26 (first wavelength plate).

[0051] The laser module 21 emits laser light of a color and intensity corresponding to the pixel of the image projected onto the retina. As the laser module 21, for example, a full-color laser module is used. In this case, the laser module 21 includes a red laser diode, a green laser diode, a blue laser diode, and a combiner that combines the laser light emitted from each laser diode into one laser light. As the combiner, for example, a planar lightwave circuit (PLC) is used. The laser module 21 emits a laser light obtained by combining a red laser light having a red wavelength, a green laser light having a green wavelength, and a blue laser light having a blue wavelength.

[0052] The collimator lens 22 is an optical element that converts the laser light emitted from the laser module 21 into a parallel light beam. The movable mirror 23 is a component for performing scanning based on the light beam converted by the collimator lens 22. The movable mirror 23 is provided in the emission direction of the light beam converted by the collimator lens 22. As the movable mirror 23, for example, a MEMS (Micro Electro Mechanical Systems) mirror is used.

[0053] The wavelength plate 26 is an optical element that converts linear polarization into circular polarization. Since the laser module 21 generally emits linear polarization, it is necessary to convert the linear polarization into circular polarization until the light reaches the Pancharatnam-Berry phase optical element 44 (described below) in the optical unit 4. Therefore, the wavelength plate 26 is arranged between the laser module 21 and the optical unit 4. The wavelength plate 26 can also be arranged, for example, immediately after the collimating lens 22. In the case where an element based on the action under linear polarization is provided between the laser module 21 and the optical unit 4, the wavelength plate 26 is provided at a later stage than the element based on the action under linear polarization. As the wavelength plate 26, a true 1 / 4 wavelength plate is used in consideration of wavelength dispersion, etc., but a 1 / 4+N (N is a natural number) wavelength plate can also be used.

[0054] Furthermore, the projector module 2 further includes a laser driver (not shown) that drives the laser module 21 , and a mirror driver (not shown) that drives the movable mirror 23 .

[0055] The projection lens 3 is an optical element that focuses the light beam emitted from the projector module 2 at a focus position P. The focus position P refers to the position where the light beam is focused on a cross section including the central axis of the light beam. When the light beam is focused on one point, the focus position P is an intermediate imaging plane. Here, for the sake of simplicity, the case where the focus position P is an intermediate imaging plane is exemplified.

[0056] The optical unit 4 is a unit for changing the traveling direction of the light beam according to the position of the pupil PP of the user. The position of the pupil PP is the position of the pupil PP in the eyeball E, and can also be expressed as the direction of the pupil PP or the direction of the line of sight. The optical unit 4 is configured to overlap with the focus position P. The optical unit 4 includes a deflection element 41. The deflection element 41 is an optical element that changes the traveling direction of the light beam. The details of the deflection element 41 will be described later.

[0057] The optical device 5 is an optical element that converts the light beam into parallel light and irradiates the light beam to the user's retina. The optical device 5 can be an eyepiece or a combiner.

[0058] The controller 10 is a device that performs unified control of the retinal projection device 1. The controller 10 adjusts the traveling direction of the light beam based on the deflection element 41 according to the position of the user's pupil PP. The controller 10 adjusts the traveling direction of the light beam by, for example, changing the voltage applied to the deflection element 41. The retinal projection device 1 may also include a detection unit (not shown) that detects the position of the pupil PP. Figure 1 , position EP1 and position EP2 are exemplified as the position of the pupil PP.

[0059] Next, refer to Figure 2 to Figure 5 , the details of the deflection element 41 are described. Figure 2 It is a rough representation Figure 1 A diagram of the structure of the deflection element is shown. Figure 3 It is a rough representation Figure 2 Figure 2 shows the structure of the wave plate. Figure 4 It is a rough representation Figure 2 The diagram shows the structure of the Pancharatnam-Berry phase optical element (hereinafter sometimes referred to as "PBOE"). Figure 5 It is along Figure 4 Cross-sectional view of the V-V line.

[0060] like Figure 2 As shown, the deflection element 41 is a transmissive deflection element, and includes one or more wavelength plates 43 (second wavelength plates) and one or more PBOEs 44. The number of wavelength plates 43 included in the deflection element 41 is the same as the number of PBOEs 44 included in the deflection element 41.

[0061] The wavelength plate 43 is an optical element that can switch between a state of preserving (maintaining) the polarization state (polarity) of the circularly polarized light passing through the wavelength plate 43 and a state of converting the circularly polarized light passing through the wavelength plate 43 into circularly polarized light of opposite polarity, according to a voltage applied to the wavelength plate 43. The wavelength plate 43 has, for example, a rectangular plate shape. Figure 3 As shown, the wavelength plate 43 includes a transparent substrate 431 , a transparent substrate 432 , a transparent electrode 433 , a transparent electrode 434 , an alignment layer 435 , an alignment layer 436 , and a liquid crystal layer 437 .

[0062] The transparent substrate 431 and the transparent substrate 432 are substrates having visible light transmittance for transmitting visible light, respectively. The transparent substrate 431 and the transparent substrate 432 are made of constituent materials with small birefringence. Examples of constituent materials of the transparent substrate 431 and the transparent substrate 432 include SiO2, optical glass, and glass substrates for liquid crystal displays. The transparent substrate 431 and the transparent substrate 432 are separated from each other in the Z-axis direction and are arranged substantially in parallel. The transparent substrate 431 has a surface 431a and a surface 431b that intersect the Z-axis direction (here, orthogonal). The transparent substrate 432 has a surface 432a and a surface 432b that intersect the Z-axis direction (here, orthogonal). The surface 431a and the surface 432a face each other in the Z-axis direction. The surface 431b is the surface on the opposite side of the surface 431a. The surface 432b is the surface on the opposite side of the surface 432a.

[0063] The transparent electrode 433 and the transparent electrode 434 (a pair of transparent electrodes) are electrodes that are conductive and have visible light transmittance for transmitting visible light. As an example of the constituent material of the transparent electrode 433 and the transparent electrode 434, ITO can be cited. The transparent electrode 433 and the transparent electrode 434 face each other in the Z-axis direction with the liquid crystal layer 437 between them. The transparent electrode 433 is provided on the surface 431a. The transparent electrode 434 is provided on the surface 432a. A voltage is applied to the transparent electrode 433 and the transparent electrode 434.

[0064] The alignment layer 435 and the alignment layer 436 are layers for controlling the arrangement state (alignment) of the liquid crystal molecules Lm1 included in the liquid crystal layer 437. The alignment layer 435 is provided on the surface of the transparent electrode 433 facing the transparent electrode 434. The alignment layer 436 is provided on the surface of the transparent electrode 434 facing the transparent electrode 433.

[0065] The liquid crystal layer 437 is provided between the alignment layer 435 and the alignment layer 436. In other words, the liquid crystal layer 437 is provided between the transparent electrode 433 and the transparent electrode 434. Nematic liquid crystal can be cited as an example of a constituent material of the liquid crystal layer 437. The optical characteristics of the liquid crystal layer 437 change by controlling the alignment of the liquid crystal molecules Lm1 according to the electric field applied to the liquid crystal layer 437.

[0066] In the wavelength plate 43, the light beam is incident on the transparent substrate 431 from the surface 431b, passes through the transparent substrate 431, the transparent electrode 433, the alignment layer 435, the liquid crystal layer 437, the alignment layer 436, the transparent electrode 434, and the transparent substrate 432 in sequence, and is emitted from the surface 432b.

[0067] Since the liquid crystal material is in contact with the alignment layer 435 and the alignment layer 436, the liquid crystal molecule Lm1 is in an in-plane alignment state when no voltage is applied between the transparent electrode 433 and the transparent electrode 434 (voltage non-applied state). That is, the slow axis of the liquid crystal molecule Lm1 is substantially parallel to the plane of the alignment layer 435 and the alignment layer 436 in contact with the liquid crystal layer 437. At this time, the length (thickness) of the liquid crystal layer 437 in the Z-axis direction is adjusted so that the wavelength plate 43 functions as a 1 / 2 wavelength plate (that is, the circularly polarized light passing through the wavelength plate 43 is converted into circularly polarized light of the opposite polarity).

[0068] By applying a voltage between the transparent electrode 433 and the transparent electrode 434, an electric field in the Z-axis direction is generated in the liquid crystal layer 437, and the liquid crystal molecules Lm1 are aligned in the Z-axis direction. That is, the slow axis of the liquid crystal molecule Lm1 is substantially perpendicular to the planes of the alignment layer 435 and the alignment layer 436 in contact with the liquid crystal layer 437. Therefore, in a state where a voltage is applied between the transparent electrode 433 and the transparent electrode 434 (voltage applied state), the wavelength plate 43 retains the polarization state of the circularly polarized light passing through the wavelength plate 43.

[0069] The PBOE 44 is an optical element that converts circularly polarized light passing through the PBOE 44 into circularly polarized light of opposite polarity and diffracts the circularly polarized light in a diffraction direction corresponding to the polarity of the circularly polarized light incident on the PBOE 44. The PBOE 44 has, for example, a rectangular plate shape. Figure 4 and Figure 5 As shown, the PBOE 44 includes a transparent substrate 441, an alignment layer 442, and a liquid crystal layer 443 (liquid crystal polymer).

[0070] The transparent substrate 441 is a substrate having visible light transmittance through which visible light is transmitted. The transparent substrate 441 is composed of a constituent material having small birefringence as well as surface precision. Examples of constituent materials of the transparent substrate 441 include SiO2, optical glass, and a glass substrate for a liquid crystal display. The transparent substrate 441 has a surface 441a and a surface 441b intersecting (orthogonal in this case) the Z-axis direction.

[0071] The orientation layer 442 is a layer for controlling the arrangement state (orientation) of the liquid crystal molecules Lm2 included in the liquid crystal layer 443. The orientation layer 442 is provided on the surface 441a. Examples of the constituent material of the orientation layer 442 include materials whose molecular orientation changes by irradiation with polarized light.

[0072] The liquid crystal layer 443 is provided on the alignment layer 442. Examples of the constituent material of the liquid crystal layer 443 include nematic liquid crystal and cholesteric liquid crystal. The liquid crystal layer 443 is composed of a liquid crystal polymer obtained by aligning liquid crystal molecules using liquid crystal molecules capable of photopolymerization and then polymerizing them. Details of the manufacturing method of the PBOE 44 will be described later.

[0073] The plurality of liquid crystal molecules Lm2 included in the liquid crystal layer 443 are arranged three-dimensionally in the X-axis direction, the Y-axis direction, and the Z-axis direction. In the X-axis direction, for example, the plurality of liquid crystal molecules Lm2 are arranged in such a manner that the angle (orientation angle) formed by the lag axis of the liquid crystal molecule Lm2 and the X-axis direction gradually increases or decreases. Specifically, in the X-axis direction, within a range equivalent to the period T of the diffraction grating, the plurality of liquid crystal molecules Lm2 are arranged in such a manner that the orientation angle gradually increases from 0 degrees to 180 degrees. In the Y-axis direction and the Z-axis direction, the plurality of liquid crystal molecules Lm2 are arranged in such a manner that the orientation angles of the liquid crystal molecules Lm2 are the same. Since the phase changes by -360 degrees, i.e., 1 wavelength, due to a rotation of the orientation angle of 180 degrees, the rotation of the orientation angle by 180 degrees is equivalent to the amount of 1 period T of the diffraction grating.

[0074] Through the above structure, PBOE44 acts as a diffraction grating that diffracts circularly polarized light at a constant diffraction angle. For example, circularly polarized light is incident on the transparent substrate 441 from the surface 441b, and passes through the transparent substrate 441, the orientation layer 442 and the liquid crystal layer 443 in sequence. At this time, the circularly polarized light gradually changes to circularly polarized light of the opposite polarity through the birefringence of the liquid crystal molecule Lm2 contained in the liquid crystal layer 443. At this time, the relative phase of the circularly polarized light of the opposite polarity relative to the incident circularly polarized light changes according to the orientation angle of the liquid crystal molecule Lm2, and the amount of change is equal to -2 times the amount of change in the orientation angle of the liquid crystal molecule Lm2 (where the rotation direction of the electric field vector of the incident circularly polarized light is considered to be positive). However, the orientation angle and the phase angle are considered in radians. As a result, the circularly polarized light of the opposite polarity can have a phase difference that depends on the passing position. That is, because the slope of the wavefront can be generated, PBOE44 acts as a diffraction grating. In addition, the diffraction directions of left circularly polarized light (circularly polarized light of the first polarity) and right circularly polarized light (circularly polarized light of the second polarity) are opposite. When the deflector 41 includes a plurality of PBOEs 44, the diffraction angles by the PBOEs 44 may be different from each other.

[0075] The length (thickness) of the liquid crystal layer 443 in the Z-axis direction is set so that the phase difference caused by the birefringence of the liquid crystal is 180 degrees, that is, the PBOE44 acts as a 1 / 2 wavelength plate whose lag axis changes in the in-plane direction. As a result, the diffraction efficiency reaches nearly 100%. In this case, zero-order (straight light) is almost not generated. In the PBOE44, higher-order diffracted light of the second order or more is not generated.

[0076] The array body 42 is formed by arranging the wavelength plates 43 and the PBOE 44 alternately one by one in the Z-axis direction. The array body 42 has two ends in the Z-axis direction, namely, a first end 42a and a second end 42b. The wavelength plate 43 is arranged at the first end 42a, and the PBOE 44 is arranged at the second end 42b. When the deflection element 41 is arranged near the intermediate imaging plane, the PBOE 44 near the intermediate imaging plane among the PBOE 44 included in the deflection element 41 can also be configured to have the function of a field lens.

[0077] Next, refer to Figure 6 to Figure 9 , the beam steering (beam deflection) performed by the deflection element 41 is described. Figure 6 to Figure 9 It is used for Figure 2 Here, for the sake of convenience, the deflection element 41 includes two wavelength plates 43 and two PBOEs 44, and the left circularly polarized light beam Bin is incident on the deflection element 41. With respect to the incident direction of the light beam Bin, the left side (at Figure 6 to Figure 9 The diffraction angle (in the center is the upper side of the paper) is set to a positive value.

[0078] In the following description, it is assumed that the diffraction angle of PBOE44 does not depend on the incident angle to PBOE44. This assumption is established as a good approximation when the diffraction angle of PBOE44 is small. In fact, in PBOE44, the in-plane direction component of the wave number vector of the incident light due to diffraction changes with the inherent wave number vector of the in-plane direction determined by the orientation pattern of the liquid crystal layer 443 of PBOE44, and this change does not depend on the incident angle. Therefore, the additivity of the diffraction of PBOE44 mentioned above is not strictly about the angle, but actually about the change amount of the in-plane direction component of the wave number vector of the circularly polarized light caused by diffraction.

[0079] exist Figure 6 In the example shown, both wavelength plates 43 are set to a voltage applied state. In this case, if the light beam Bin is incident on the first wavelength plate 43, the left circularly polarized light beam B1 is emitted from the first wavelength plate 43 and is incident on the first PBOE 44. Then, the right circularly polarized light beam B2 is diffracted in the diffraction direction corresponding to the left circularly polarized light (in Figure 6 In the figure, the diffraction angle θ1 (which is on the upper side of the paper) is emitted from the first PBOE 44 and enters the second wavelength plate 43.

[0080] Then, the right circularly polarized light beam B3 is emitted from the second wave plate 43 and enters the second PBOE 44. Then, the left circularly polarized light beam Bout is diffracted in the direction corresponding to the right circularly polarized light (in Figure 6In the example, the diffraction angle θ2 is greater than the diffraction angle θ1.

[0081] exist Figure 7 In the example shown, the first wavelength plate 43 is set to a voltage non-applied state, and the second wavelength plate 43 is set to a voltage applied state. In this case, if the light beam Bin is incident on the first wavelength plate 43, the light beam B1 of right circular polarization is emitted from the first wavelength plate 43 and is incident on the first PBOE 44. Then, the light beam B2 of left circular polarization is diffracted in the diffraction direction corresponding to the right circular polarization (in Figure 7 In the figure, the diffraction angle θ1 (below the paper) is emitted from the first PBOE 44 and enters the second wavelength plate 43.

[0082] Then, the left circularly polarized light beam B3 is emitted from the second wave plate 43 and enters the second PBOE 44. Then, the right circularly polarized light beam Bout is diffracted in the direction corresponding to the left circularly polarized light (in Figure 7 In the figure, the light beam Bout is emitted from the second PBOE 44 at a diffraction angle θ2 (upper side of the paper). Therefore, the light beam Bout is emitted at a diffraction angle (θ2-θ1) relative to the incident direction of the light beam Bin.

[0083] exist Figure 8 In the example shown, the first wavelength plate 43 is set to a voltage applied state, and the second wavelength plate 43 is set to a voltage non-applied state. In this case, if the light beam Bin is incident on the first wavelength plate 43, the left circularly polarized light beam B1 is emitted from the first wavelength plate 43 and is incident on the first PBOE 44. Then, the right circularly polarized light beam B2 is diffracted in the diffraction direction corresponding to the left circularly polarized light (in Figure 8 In the figure, the diffraction angle θ1 (which is on the upper side of the paper) is emitted from the first PBOE 44 and enters the second wavelength plate 43.

[0084] Then, the left circularly polarized light beam B3 is emitted from the second wave plate 43 and is incident on the second PBOE 44. Then, the right circularly polarized light beam Bout is emitted from the second PBOE 44 at a diffraction angle θ2 corresponding to the diffraction direction of the left circularly polarized light. Therefore, the light beam Bout is emitted at a diffraction angle (θ1+θ2) relative to the incident direction of the light beam Bin.

[0085] exist Fig. 9In the example shown, both wavelength plates 43 are set to a voltage non-applied state. In this case, if the light beam Bin is incident on the first wavelength plate 43, the light beam B1 of right circular polarization is emitted from the first wavelength plate 43 and is incident on the first PBOE 44. Then, the light beam B2 of left circular polarization is diffracted in the diffraction direction corresponding to the right circular polarization (in Fig. 9 In the figure, the diffraction angle θ1 (below the paper) is emitted from the first PBOE 44 and enters the second wavelength plate 43.

[0086] Then, the right circularly polarized light beam B3 is emitted from the second wave plate 43 and enters the second PBOE 44. Then, the left circularly polarized light beam Bout is emitted from the second PBOE 44 at a diffraction angle θ2 corresponding to the diffraction direction of the right circularly polarized light. Therefore, the light beam Bout is emitted at a diffraction angle (-θ1-θ2) relative to the incident direction of the light beam Bin.

[0087] In this way, by switching the state of each wavelength plate 43 between the voltage applied state and the voltage non-applied state, the traveling direction of the light beam passing through the deflection element 41 is changed. The traveling direction of the light beam passing through the deflection element 41 can be switched to two or more directions depending on the number n of the sets of wavelength plates 43 and PBOEs 44 included in the optical unit 4. n The direction of travel of the group.

[0088] Next, refer to Fig.10 , the effects of the retinal projection device 1 are described. Fig.10 This is a diagram used to explain the change in the wave number vector caused by deflection. Fig.10 As shown in FIG. 1 , if the deflection is performed at a position separated from the focus position P, the focus at the (imaginary) focus point generated when the deflected light beam is extended forward and backward along the traveling axis is incomplete, and spherical aberration occurs. This is because the optical system configured in the subsequent stage is designed to eventually convert the light diverging from the focus point into parallel light. If the focusing is incomplete, the conversion into parallel light is also incomplete. Here, it is expressed as "spherical aberration". On the other hand, if the deflection is performed at the focus position P, the spherical aberration is reduced.

[0089] In the retinal projection device 1 described above, the optical unit 4 including the deflection element 41 is arranged in a manner overlapping with the focus position P, and the traveling direction of the light beam based on the deflection element 41 is adjusted according to the position of the user's pupil PP. According to this structure, even if the user moves his eyes, the traveling direction of the light beam can be changed to follow the movement of the user's pupil PP. Since the deflection element 41 is arranged near the focus position P, the spherical aberration caused by changing the traveling direction (deflection) of the light beam is reduced. Therefore, since the quality of the image on the retina is maintained, the user can correctly recognize the image. As a result, the eye box can be expanded.

[0090] By switching the wavelength plate 43 between a state in which the polarization state of the circularly polarized light is preserved (voltage non-applied state) and a state in which the circularly polarized light is converted into circularly polarized light of opposite polarity (voltage applied state), the polarity (polarization state) of the circularly polarized light passing through the wavelength plate 43 can be switched. The diffraction direction in the PBOE 44 provided at the subsequent stage of the wavelength plate 43 is determined according to the polarity of the circularly polarized light. Therefore, by applying a voltage to each wavelength plate 43, the traveling direction of the light beam can be selected from the number of traveling directions corresponding to the number n of the sets of the wavelength plates 43 and the PBOE 44 included in the optical unit 4.

[0091] In the wavelength plate 43, a liquid crystal layer 437 is provided between a transparent substrate 431 and a transparent substrate 432. According to this structure, by applying a voltage between the transparent substrate 431 and the transparent substrate 432, an electric field is generated in the liquid crystal layer 437, and the liquid crystal molecules Lm1 included in the liquid crystal layer 437 are oriented in the direction of the electric field. Therefore, in a state where a voltage is applied between the transparent substrate 431 and the transparent substrate 432, the wavelength plate 43 preserves the polarization state of the circularly polarized light passing through the wavelength plate 43. In a state where a voltage is not applied between the transparent substrate 431 and the transparent substrate 432, the liquid crystal molecules Lm1 included in the liquid crystal layer 437 are in an in-plane orientation state. At this time, the wavelength plate 43 converts the circularly polarized light passing through the wavelength plate 43 into circularly polarized light of the opposite polarity. In this way, the state of preserving the polarization state of the circularly polarized light and the state of converting the circularly polarized light into circularly polarized light of the opposite polarity can be switched according to the presence or absence of the voltage applied between the transparent substrate 431 and the transparent substrate 432.

[0092] The PBOE 44 is made of a liquid crystal polymer. By using a liquid crystal polymer, the PBOE 44 can be easily formed.

[0093] The projector module 2 emits laser light obtained by combining red laser light, green laser light, and blue laser light, thereby realizing a full-color retinal projection device 1 .

[0094] exist Figure 6 to Figure 9 In the example shown, each PBOE 44 is capable of diffracting circularly polarized light in the X-axis direction. According to this structure, it is possible to follow the change of the viewpoint in the X-axis direction. In order to follow the change of the viewpoint in the Y-axis direction, the deflection element 41 may also include a PBOE 44 capable of diffracting circularly polarized light in the Y-axis direction. The deflection element 41 may also include a PBOE 44 capable of diffracting circularly polarized light in the X-axis direction and a PBOE 44 capable of diffracting circularly polarized light in the Y-axis direction. In this case, two-dimensional beam steering is achieved on the XY plane.

[0095] like Fig.11As shown in FIG. 1 , when a Kepler optical system having different magnifications in the X-axis direction and the Y-axis direction is used as the projection lens 3, no intermediate imaging plane is formed. In this case, the focus position Px where the light beam is focused in the X-axis direction is separated from the focus position Py where the light beam is focused in the Y-axis direction. The focus position Px has a linear shape extending in the Y-axis direction. The focus position Py has a linear shape extending in the X-axis direction.

[0096] The farther the position of the deflection element 41 is from the focusing position, the greater the aberration of the wavefront caused by the deflection. Therefore, the deflection element 41 capable of diffracting circularly polarized light in the X-axis direction may also be set at the focusing position Px, and the deflection element 41 capable of diffracting circularly polarized light in the Y-axis direction may also be set at the focusing position Py. In other words, the optical unit 4 may also include a deflection element 41 that is set at the focusing position Px and capable of diffracting circularly polarized light in the X-axis direction, and a deflection element 41 that is set at the focusing position Py and capable of diffracting circularly polarized light in the Y-axis direction. According to this structure, the position of the deflection element 41 that can diffract circularly polarized light in the X-axis direction is close to the focusing position Px, and the position of the deflection element 41 that can diffract circularly polarized light in the Y-axis direction is close to the focusing position Py. Therefore, the aberration of the wavefront caused by the deflection can be suppressed, so the cost required for correcting the aberration can be reduced.

[0097] Next, refer to Fig.12 , a structure capable of following changes in the viewpoint in the Z-axis direction (front-back direction) is described. Fig.12 FIG. 2 is a diagram showing the basic structure of a retinal projection device according to a modified example. Fig.12 As shown, the retinal projection device 1 of the modified example is different from the retinal projection device 1 of the above-described embodiment mainly in that the optical unit 4 further includes a deflection element 45 .

[0098] The deflector 45 mainly differs from the deflector 41 in that it includes a PBOE 44 functioning as a meniscus lens instead of a PBOE 44 functioning as a diffraction grating that diffracts at a constant diffraction angle. As a method for determining the alignment of the liquid crystal molecules Lm2 for realizing such a PBOE 44, for example, the following method is used.

[0099] In general, the lens function corresponds to the phase shift amount before and after the light passes through each in-plane position. On the other hand, in PBOE44, the polarity of the circularly polarized light is reversed due to the transmission of the light, and thus the rotation direction of the electric field vector is reversed. Specifically, the electric field vector obtained by acquiring an image for an axis perpendicular to the slow axis of the electric field vector of the incident circularly polarized light determined according to the orientation direction of the liquid crystal molecule Lm2 becomes the electric field vector of the circularly polarized light of the opposite polarity converted by PBOE44. Therefore, the change in the in-plane direction of the phase shift amount before and after the light passes through each of the above-mentioned in-plane positions is consistent with -2 times the rotation amount of the orientation azimuth of the liquid crystal molecule Lm2 in the in-plane direction (the polarity of the rotation direction sets the rotation direction of the electric field vector of the incident circularly polarized light to positive.). Therefore, by arbitrarily determining the orientation direction of the liquid crystal molecule Lm2 at a certain point, the orientation direction of the liquid crystal molecule Lm2 at other points must be determined by the required lens function. Based on this concept, for example, the PBOE that functions as a convex lens when the incident light is right circularly polarized light is designed by setting the alignment azimuth of the liquid crystal molecules Lm2 to rotate clockwise from the center toward the periphery when viewed from the incident surface.

[0100] The PBOE 44 functions as a convex lens for right circularly polarized light and as a concave lens for left circularly polarized light. The plurality of PBOEs 44 included in the deflection element 45 are configured to have different focal lengths, and can correspond to the positions of a plurality of viewpoints in the Z-axis direction. Fig.12 , position EP3 and position EP4 are exemplified as the position of the pupil PP.

[0101] In the modified example, the retinal projection device 1 has the same structure as the retinal projection device 1 of the above embodiment, and achieves the same effect as the retinal projection device 1 of the above embodiment. In the modified example, the retinal projection device 1 can also follow the change of the viewpoint in the Z-axis direction because the optical unit 4 includes the deflection element 45. That is, even if the distance between the optical device 5 and the user's pupil PP changes, the field of view can be ensured. For example, when the retinal projection device 1 is applied to a near-eye display such as smart glasses, the installation deviation of the near-eye display can be allowed.

[0102] Next, refer to Fig.13 , an application example of the retinal projection device is described. Fig.13 Yes means Figure 1 FIG. 1 is a diagram showing an application example of a retinal projection device. Fig.13 The retinal projection device 1A shown can be applied to near-eye displays such as smart glasses. Fig.13 In the figure, the controller 10 is omitted.

[0103] In the retinal projection device 1A, the optical device 5 is a combiner. The optical device 5 includes a transparent substrate 51 and a reflector 52. The transparent substrate 51 is a substrate having visible light transmittance that transmits visible light. Examples of the constituent material of the transparent substrate 51 include SiO2, optical glass, and optical plastic. The transparent substrate 51 has a surface 51a facing the eyeball E of the user who installs the near-eye display. The transparent substrate 51 can also be a lens of smart glasses. The reflector 52 is provided on the surface 51a and functions as a semi-transparent concave mirror. The reflector 52 is a reflective diffraction grating layer such as a polarization-dependent volume diffraction grating (Polarization Volume Grating: PVG).

[0104] The projector module 2 further includes a wavefront correction lens 24 (wavefront correction unit). The wavefront correction lens 24 is a lens that corrects the aberration of the wavefront of the light rays (corresponding to the light rays at the center of the field of view) passing through the pupil PP among the light rays constituting the light beam. The wavefront correction lens 24 corrects the aberration three or more times, for example. The wavefront correction lens 24 is disposed between the collimating lens 22 and the movable mirror 23. The wavefront correction lens 24 is disposed, for example, in front of the movable mirror 23. The wavefront correction lens 24 is composed of a liquid crystal lens.

[0105] In the wavefront correction lens 24, the area through which the light ray Rc1 passes and the area through which the light ray Rc2 passes are close to each other. The light ray Rc1 is a light ray corresponding to the center of the visual field when the pupil PP is located at the position EP1. The light ray Rc2 is a light ray corresponding to the center of the visual field when the pupil PP is located at the position EP2. Therefore, the wavefront correction lens 24 adaptively corrects the aberration of the wavefront according to the position of the pupil PP. Specifically, the controller 10 (refer to Figure 1 ) The wavefront correction lens 24 is controlled according to the position of the user's pupil PP so that the wavefront error of the light beam that constitutes the pixels on the line of sight, that is, in the direction of the gaze point, among the light beams passing through the pupil PP is minimized.

[0106] The optical unit 4 further includes a field lens 46. The field lens 46 is a lens that changes the traveling direction of the light beam near the focus of the light beam. The field lens 46 is provided at the second end 42b (output end) of the array body 42. Specifically, the field lens 46 is provided to cover the PBOE 44 at the second end 42b.

[0107] The retinal projection device 1A further includes a wavelength plate 9 (first wavelength plate) to replace the wavelength plate 26. The wavelength plate 9 is an optical element that converts linear polarization into circular polarization. The wavelength plate 9 is arranged between the laser module 21 and the optical unit 4. In the case where an element based on the action under linear polarization is provided between the laser module 21 and the optical unit 4, the wavelength plate 9 is arranged at a later stage than the element based on the action under linear polarization. As the wavelength plate 9, a true 1 / 4 wavelength plate is used in consideration of wavelength dispersion, etc., but a 1 / 4+N (N is a natural number) wavelength plate may also be used.

[0108] The retinal projection device 1A further includes a relay lens 6 (focusing unit) and a wavefront correction lens 7 (wavefront correction unit). The relay lens 6 is a lens that focuses the light beam emitted from the optical unit 4. The relay lens 6 is provided between the optical unit 4 and the optical device 5. The relay lens 6 is composed of a lens group that functions as a convex lens or a convex lens.

[0109] The wavefront correction lens 7 is a lens that mainly corrects the viewing angle dependency of the focus of the light beam, that is, the viewing angle dependency of the visibility in the retina, and the change caused by the switching of the deflection element 41. The wavefront correction lens 7 is arranged between the projection lens 3 and the optical unit 4. The wavefront correction lens 7 is arranged, for example, immediately after the projection lens 3. The wavefront correction lens 7 may also be arranged before the projection lens 3. The wavefront correction lens 7 is composed of a liquid crystal lens.

[0110] exist Fig.13 In the example shown, the wavefront aberration of each of the light beam Rc1 and the light beam Rc2 is corrected. In addition, the wavefront correction lens 7 is configured to correct the wavefront aberration adaptively according to the position of the pupil PP, similarly to the wavefront correction lens 24.

[0111] In the retinal projection device 1A, the same effect as that of the retinal projection device 1 is achieved for the structure common to the retinal projection device 1. The retinal projection device 1A further includes a wavefront correction lens 7 and a wavefront correction lens 24. Therefore, the resolution at the center of the field of view can be improved. The wavefront correction lens 7 and the wavefront correction lens 24 are composed of liquid crystal lenses. By using liquid crystal lenses, the wavefront correction lens 7 and the wavefront correction lens 24 can be easily realized. In the case of using liquid crystal lenses, many liquid crystal lenses act on linear polarized light, not circularly polarized light, and therefore, a wavelength plate that converts linear polarized light into circularly polarized light is configured between the liquid crystal lens and the optical unit 4.

[0112] The wavefront correction lens 7 mainly corrects the change caused by the switch of the deflection element 41 in the visual angle dependence of the focus of the light beam, that is, the visual angle dependence of the visibility in the retina. The function of the wavefront correction lens 7 is to correct the change of the image forming position on the retina (in front of or behind the retina) depending on the incident angle to the pupil PP, which is caused by the change of the aberration of the optical system of the retinal projection device 1A due to the switch of the deflection element 41, or by the aberration of the naked eye. In particular, the wavefront correction lens 7 can cope with the situation that the focus of the naked eye is easily shifted to the back side of the retina at the periphery of the visual field relative to the center of the visual field due to myopia of the type of elongated eye axis. This correction can also be performed using a fixed function lens like a conventional progressive diopter glasses, but if the line of sight moves up, down, left, and right, the correction becomes inappropriate, so the correction effect is not obvious. On the other hand, the wavefront correction lens 7 can be corrected in accordance with the movement of the line of sight by using a variable lens such as a liquid crystal lens.

[0113] A variable wavefront correction lens 24 is provided between the collimating lens 22 and the movable mirror 23. Fig.13 As shown, it is possible to effectively correct the third or more aberrations caused by the light beam obliquely incident on the optical element such as the combiner 5. The aberration depends on the angle and position of the light beam, but the wavefront correction function of the wavefront correction lens 24 can also be set so that the light beam at the angle and position consistent with the line of sight when incident on the pupil PP is optimally corrected. In this case, since the resolution is low outside a very narrow range around the line of sight of the naked eye, practical problems arise. Therefore, the controller 10 detects the position and angle of the pupil PP, controls the light beam to reach the position of the pupil PP through the deflection performed by the optical unit 4, and controls the resolution of the center of the visual field of the naked eye to be kept high through the wavefront correction lens 24.

[0114] The retinal projection device 1A includes a wavefront correction lens 7 and a wavefront correction lens 24, and the wavefront correction lens 7 and the wavefront correction lens 24 share functions. In addition, the controller 10 controls the wavefront correction lens 24 to perform the best correction on the light beam of the pixel at the center of the visual field of the naked eye, that is, forming the focus point on the retina. If the wavefront correction lens 24 can operate at a frequency that can follow the operating frequency of the movable mirror 23, the wavefront correction can be completely performed on all the light beams, and the focus adjustment of each light beam can also be performed. In this case, the wavefront correction lens 24 can also include the function of the wavefront correction lens 7, so the wavefront correction lens 7 can be omitted.

[0115] If the spatial separation of light beams with different viewing angles is well maintained at the position of the wavefront correction lens 7, the wavefront correction lens 7 may be disposed before or after the relay lens 6 at the subsequent stage of the deflection element 41. In this case, an element (wave plate) that converts the circularly polarized light from the deflection element 41 into appropriate linearly polarized light is disposed at the preceding stage. In the case where the wavefront correction lens 7 is disposed at the subsequent stage of the deflection element 41, the wavelength plate 9 may be disposed between the wavefront correction lens 24 and the optical unit 4, or may be disposed after the collimating lens 22.

[0116] The focal point FP of the optical device 5 is located in front of the optical device 5. Therefore, when the relay lens 6 is not provided, the optical unit 4 needs to be arranged at the focal point FP. In this case, the optical unit 4 may block the user's field of view. In contrast, in the retinal projection device 1A, the relay lens 6 is provided between the optical unit 4 and the optical device 5. With this structure, the optical unit 4 can be arranged at a position separated from the optical device 5. Therefore, the degree of freedom of arrangement of the optical unit 4 can be increased, and the user's field of view can be ensured.

[0117] Next, refer to Fig.14 , another application example of the retinal projection device is described. Fig.14 Yes means Figure 1 FIG. 5 is a diagram showing another application example of the retinal projection device. Fig.14 The retinal projection device 1B shown is different from the retinal projection device 1A mainly in that the reflector 52 is a concave mirror instead of a reflective diffraction grating layer, the wavefront correction lens 7 is not included, and the projector module 2 includes a wavelength plate 26 instead of a wavelength plate 9. The retinal projection device 1B can be applied to near-eye displays such as smart glasses. In addition, Fig.14 In the figure, the controller 10 is omitted.

[0118] In the retinal projection device 1B, the same effect as that of the retinal projection device 1A is achieved with respect to the common structure with the retinal projection device 1A. In the retinal projection device 1B, the reflector 52 is a concave mirror. Compared with the holographic combiner, the concave mirror causes less focus change caused by the switching of the deflection element 41. In the retinal projection device 1B, the projector module 2 includes a wavefront correction lens 24. Because the wavefront correction lens 24 adaptively corrects the aberration of the wavefront according to the position of the pupil PP, the resolution at the center of the field of view can be further improved. The wavefront correction lens 24 is composed of a liquid crystal lens. By using a liquid crystal lens, the wavefront correction lens 24 can be easily realized.

[0119] Next, refer to Fig.15 , another application example of the retinal projection device is described. Fig.15 Yes means Figure 1A diagram of yet another application example of the retinal projection device shown. Fig.15 The retinal projection device 1C shown in the figure is different from the retinal projection device 1B mainly in that the projector module 2 includes a reflective wavefront correction element 25 (wavefront correction unit) instead of the wavefront correction lens 24. The retinal projection device 1C can be applied to near-eye displays such as smart glasses. Fig.15 In the figure, the controller 10 is omitted.

[0120] The wavefront correction element 25 is an optical element that corrects the aberration of the wavefront of the light beam that passes through the pupil PP (equivalent to the light beam at the center of the field of view) among the light beams constituting the light beam. The wavefront correction element 25 corrects the aberration three or more times, for example. The wavefront correction element 25 reflects the light beam emitted from the collimating lens 22 and irradiates it to the movable mirror 23. The wavefront correction element 25 is, for example, composed of a variable shape mirror. As examples of variable shape mirrors, a MEMS type variable shape mirror and a piezoelectric element type variable shape mirror can be cited. The wavefront correction element 25 can also be composed of LCOS.

[0121] In the retinal projection device 1C, the same effect as that of the retinal projection device 1B is achieved with respect to the common structure with the retinal projection device 1B. In the retinal projection device 1C, the projector module 2 includes a wavefront correction element 25. Since the wavefront correction element 25 adaptively corrects the aberration of the wavefront according to the position of the pupil PP, the resolution at the center of the field of view can be further improved. The wavefront correction element 25 is composed of a variable shape mirror or LCOS. By using a variable shape mirror or LCOS, the wavefront correction element 25 can be easily realized.

[0122] Next, refer to Figure 16 to Figure 18 , another application example of the retinal projection device is described. Fig.16 Yes means Figure 1 A diagram of yet another application example of the retinal projection device shown. Fig.17 It is a rough representation Fig.16 A diagram of the structure of the deflection element is shown. Fig.18 It is used for Fig.16 A diagram illustrating the operation of the deflection element shown. Fig.16 The retinal projection device 1D shown in the figure mainly differs from the retinal projection device 1A in that it includes an optical unit 4A instead of the optical unit 4 and further includes a beam splitter 8. The retinal projection device 1D can be applied to near-eye displays such as smart glasses. Fig.16 In the figure, the controller 10 is omitted.

[0123] The beam splitter 8 is provided between the projection lens 3 and the optical unit 4A. The beam splitter 8 is, for example, a half-mirror beam splitter. The beam splitter 8 transmits the light beam emitted from the projection lens 3 and reflects the light beam emitted from the optical unit 4A.

[0124] The optical unit 4A mainly differs from the optical unit 4 in that it includes a deflection element 41A instead of the deflection element 41 and in the arrangement of a field lens 46. The field lens 46 is provided at the first end 42a. Specifically, the field lens 46 is provided to cover the wavelength plate 43 located at the first end 42a. The deflection element 41A is a reflective deflection element.

[0125] like Fig.17 As shown, the deflection element 41A is different from the deflection element 41 mainly in that it also includes a reflector 47. The reflector 47 is an optical element that reflects the circularly polarized light while preserving (maintaining) the polarity of the circularly polarized light. The reflector 47 is called an HPM (Handedness Preserving Mirror). The reflector 47 is arranged at the second end 42b (one end) of the arrangement body 42. Specifically, the reflector 47 overlaps with the PBOE 44 located at the second end 42b. As an example of the reflector 47, a PPAM (Polarization Preserving Anisotropic Mirror) can be cited. The PPAM is formed by alternately stacking a plurality of films having an in-plane birefringence and a thickness of approximately 1 / 4 wavelength so that the slow axes are orthogonal to each other. The reflector 47 can also be formed by overlapping a 1 / 4 wavelength plate with the mirror surface of a conventional mirror.

[0126] Reference Fig.18 , the beam steering (beam deflection) performed by the deflection element 41A is described. Here, for the sake of convenience, the deflection element 41A includes two wavelength plates 43 and two PBOEs 44, and the right circularly polarized light beam Bin is incident on the deflection element 41A. Fig.18 In the example shown, both of the two wave plates 43 are set to the voltage applied state.

[0127] In this case, if the light beam Bin is incident on the first wavelength plate 43, the light beam B1 of right circular polarization is emitted from the first wavelength plate 43 and is incident on the first PBOE 44. Then, the light beam B2 of left circular polarization is diffracted in the direction corresponding to the right circular polarization (in Fig.18 The diffraction angle θ1 of the left circular polarized light is emitted from the first PBOE 44 and enters the second wavelength plate 43. Then, the left circular polarized light beam B3 is emitted from the second wavelength plate 43 and enters the second PBOE 44. Then, the right circular polarized light beam B4 is diffracted in the direction corresponding to the left circular polarized light (in Fig.18 In the figure, the diffraction angle θ2 (on the lower side of the paper) is emitted from the second PBOE44.

[0128] Then, the light beam B4 is reflected by the reflector 47 while maintaining the polarization state, and is emitted from the reflector 47 as the light beam B5 and enters the second PBOE 44. Then, the light beam B6 of the left circular polarization is diffracted in the direction corresponding to the right circular polarization (in Fig.18 The diffraction angle θ2 of the left circular polarized light is emitted from the second PBOE 44 and enters the second wavelength plate 43. Then, the left circular polarized light beam B7 is emitted from the second wavelength plate 43 and enters the first PBOE 44. Then, the right circular polarized light beam B8 is diffracted in the direction corresponding to the left circular polarized light (in Fig.18 The light beam Bout of right circularly polarized light is emitted from the first PBOE 44 at a diffraction angle θ1 (in the figure, the diffraction angle θ1 is on the upper side of the paper), and enters the first wave plate 43. Then, the light beam Bout of right circularly polarized light is emitted from the first wave plate 43.

[0129] Therefore, the light beam Bout is emitted at a diffraction angle (2×θ1-2×θ2) in a direction that is the reverse of the incident direction of the light beam Bin. In addition, in this example, the diffraction angle θ1 is greater than the diffraction angle θ2. In this way, in the deflection element 41A, the light beam passes through the same PBOE 44 twice. Therefore, the change in the wave number vector based on the deflection element 41A becomes twice the change in the wave number vector based on the deflection element 41.

[0130] In the above description, it is assumed that the diffraction angle of PBOE44 does not depend on the incident angle to PBOE44. This assumption is established as a good approximation when the diffraction angle of PBOE44 is small. In fact, in PBOE44, the in-plane direction component of the wave number vector of the incident light due to diffraction changes with the inherent wave number vector of the in-plane direction determined by the orientation pattern of the liquid crystal layer 443 of PBOE44, and this change does not depend on the incident angle. Therefore, the additivity of the diffraction of PBOE44 mentioned above is not strictly about the angle, but actually about the change in the in-plane direction component of the wave number vector of the circularly polarized light caused by diffraction. That is, to be precise, in the above-mentioned reflective deflection element 41A, the change in the in-plane direction component of the wave number vector is doubled.

[0131] In the retinal projection device 1D, the light beam emitted from the projection lens 3 passes through the beam splitter 8 and enters the optical unit 4A, where it is deflected. Then, the light beam emitted from the optical unit 4A is reflected by the beam splitter 8 and enters the optical device 5 via the relay lens 6 .

[0132] When the deflector 41A is arranged near the intermediate imaging plane, the PBOE 44 near the intermediate imaging plane among the PBOEs 44 included in the deflector 41A may be configured to function as a field lens. In this case, the optical unit 4A may not include the field lens 46 .

[0133] In the retinal projection device 1D, regarding the common structure with the retinal projection device 1A, the same effect as that of the retinal projection device 1A is achieved. In the case where a reflector that reverses the circularly polarized light is provided at the second end 42b, the deflection obtained when the light beam passes through the array body 42 from the first end 42a toward the second end 42b is offset by the deflection obtained when the light beam passes through the array body 42 from the second end 42b toward the first end 42a. On the other hand, in the retinal projection device 1D, a reflector 47 that reflects the circularly polarized light while preserving the polarity of the circularly polarized light is provided at the second end 42b of the array body 42.

[0134] According to this structure, the light beam that has passed through the array body 42 from the first end 42a toward the second end 42b is reflected by the reflector 47 in a state where the polarization state is preserved, and passes through the array body 42 again from the second end 42b toward the first end 42a. In the deflection element 41A, since the light beam in the same polarization state passes through the same PBOE 44 twice, the change amount of the in-plane direction component of the wave number vector based on the deflection element 41A becomes twice the change amount of the in-plane direction component of the wave number vector based on the deflection element 41.

[0135] Next, refer to Fig.19 and Fig. 20 , another application example of the retinal projection device is described. Fig.19 Yes means Figure 1 A diagram of yet another application example of the retinal projection device shown. Fig. 20 It roughly indicates Fig.19 Figure 2 shows the structure of the notch filter. Fig.19 The retinal projection device 1E shown in the figure mainly differs from the retinal projection device 1A in that it includes an optical device 5A instead of the optical device 5, and further includes an extinction filter 11, a wavelength plate 12, and a notch filter 13. The retinal projection device 1E can be applied to near-eye displays such as smart glasses. Fig.19 In the figure, the controller 10 is omitted.

[0136] The extinction filter 11 is a filter for attenuating the light reflected by the notch filter 13. The stray light can be reduced by the extinction filter 11. The wavelength plate 12 is an optical element that converts the polarization state of the light beam emitted from the optical unit 4 from circular polarization to linear polarization. The wavelength plate 12 is, for example, a 1 / 4 wavelength plate. An absorption type linear polarizer may be used instead of the wavelength plate 12.

[0137] The notch filter 13 is a circularly polarized light dependent notch filter, and is a filter for removing unnecessary circularly polarized light components from light of a red wavelength (hereinafter, sometimes referred to as "red light Lr"), light of a green wavelength (hereinafter, sometimes referred to as "green light Lg"), and light of a blue wavelength (hereinafter, sometimes referred to as "blue light Lb"), and extracting desired circularly polarized light components. The notch filter 13 has the following functions: passing left circularly polarized light in the red light Lr and reflecting right circularly polarized light, passing right circularly polarized light in the green light Lg and reflecting left circularly polarized light, and passing left circularly polarized light in the blue light Lb and reflecting right circularly polarized light.

[0138] like Fig. 20 As shown, the notch filter 13 includes a transparent substrate 31, a filter layer 32 (third filter layer), a filter layer 33 (second filter layer), and a filter layer 34 (first filter layer).

[0139] The transparent substrate 31 is a substrate having visible light transmittance through which visible light is transmitted. The transparent substrate 31 is made of a constituent material with low birefringence. Examples of constituent materials of the transparent substrate 31 include SiO2, optical glass, and a glass substrate for a liquid crystal display. The transparent substrate 31 has a surface 31a and a surface 31b. The surface 31b is a surface on the opposite side of the surface 31a.

[0140] The filter layer 32 is a layer that reflects right circular polarized light from the blue light Lb, removes the right circular polarized light, and extracts the left circular polarized light. The filter layer 32 is arranged on the surface 31a. The filter layer 32 is a cholesteric liquid crystal polymer layer, which is PVG. The cholesteric liquid crystal polymer layer of the filter layer 32 has a spiral structure, and the spiral structure has a spiral pitch corresponding to the blue wavelength, and the spiral structure is twisted in the twisting direction of the reflected right circular polarized light. It is expected that the direction of the spiral axis is parallel to the direction of the light of the center of the light beam that comes to the center of the visual field and the center of the pupil PP when the line of sight is facing the front. In addition, the "direction of the spiral axis" refers to the direction in which the spiral axis extends, and in the following description, it is referred to as the "direction of the spiral axis". The "twisting direction" indicates the direction of the twist in the sense of whether it is a right-hand thread or a left-hand thread.

[0141] The filter layer 33 is a layer that reflects the left circularly polarized light from the green light Lg, removes the left circularly polarized light, and extracts the right circularly polarized light. The filter layer 33 is provided on the filter layer 32. The filter layer 33 is a cholesteric liquid crystal polymer layer, which is PVG. The cholesteric liquid crystal polymer layer of the filter layer 33 has a helical structure having a helical pitch corresponding to the wavelength of green, and the helical structure is twisted in the twisting direction of the reflected left circularly polarized light.

[0142] The filter layer 34 is a layer that reflects right circularly polarized light from the red light Lr, removes the right circularly polarized light, and extracts left circularly polarized light. The filter layer 34 is provided on the filter layer 33. The filter layer 34 is a cholesteric liquid crystal polymer layer, which is PVG. The cholesteric liquid crystal polymer layer of the filter layer 34 has a helical pitch, which has a helical pitch corresponding to the wavelength of red, and the helical pitch is twisted in the twisting direction of the reflected right circularly polarized light.

[0143] The optical device 5A is a holographic combiner. In the present embodiment, the optical device 5A has the following functions: scattering left circularly polarized light in a wavelength range including red wavelengths (first wavelength range), scattering right circularly polarized light in a wavelength range including green wavelengths (second wavelength range), and scattering left circularly polarized light in a wavelength range including blue wavelengths (third wavelength range). The optical device 5A is different from the optical device 5 mainly in that the reflector 53 is included instead of the reflector 52.

[0144] The reflector 53 is provided on the surface 51a and functions as a semi-transparent concave mirror similarly to the reflector 52. The reflector 53 includes a hologram diffraction layer 54 (third hologram diffraction layer), a hologram diffraction layer 55 (second hologram diffraction layer), and a hologram diffraction layer 56 (first hologram diffraction layer).

[0145] The holographic diffraction layer 54 is a reflective diffraction grating layer that scatters (reflects) left circularly polarized light in a wavelength range including a blue wavelength. The holographic diffraction layer 54 does not scatter right circularly polarized light in the above wavelength range. The holographic diffraction layer 54 is composed of a cholesteric liquid crystal polymer layer having a helical structure having a helical pitch corresponding to the blue wavelength and twisted in a twisting direction for reflecting left circularly polarized light.

[0146] The holographic diffraction layer 55 is a reflective diffraction grating layer that scatters (reflects) right circularly polarized light in a wavelength range including a green wavelength. The holographic diffraction layer 55 is stacked on the holographic diffraction layer 54. The holographic diffraction layer 55 does not scatter left circularly polarized light in the above wavelength range. The holographic diffraction layer 55 is composed of a cholesteric liquid crystal polymer layer having a helical structure having a helical pitch corresponding to the green wavelength and twisted in a twisting direction for reflecting right circularly polarized light.

[0147] The holographic diffraction layer 56 is a reflective diffraction grating layer that scatters (reflects) left circularly polarized light in a wavelength range including a red wavelength. The holographic diffraction layer 56 does not scatter right circularly polarized light in the above wavelength range. The holographic diffraction layer 56 is composed of a cholesteric liquid crystal polymer layer having a helical structure having a helical pitch corresponding to the red wavelength and twisted in a twisting direction for reflecting left circularly polarized light.

[0148] The holographic diffraction layer 54, the holographic diffraction layer 55, and the holographic diffraction layer 56 are sequentially stacked on the surface 51a. Specifically, the holographic diffraction layer 54 is provided on the surface 51a. The holographic diffraction layer 55 is stacked on the holographic diffraction layer 54. The holographic diffraction layer 56 is stacked on the holographic diffraction layer 55. In addition, the stacking order of the holographic diffraction layer 54, the holographic diffraction layer 55, and the holographic diffraction layer 56 can also be switched arbitrarily.

[0149] Here, refer to Fig.21 and Fig. 22 , the cholesteric liquid crystal polymer layer in the notch filter 13 is described in detail. Fig.21 It is a diagram of Ewald spheres of various colors in the wave number space of light observed on a cross section including the wave number vector of the helical axis direction of the cholesteric liquid crystal polymer layer and the wave number vector of the center of the light beam that becomes the center of the field of view in the incident light. Ewald sphere ESr is the Ewald sphere of red light. Ewald sphere ESg is the Ewald sphere of green light. Ewald sphere ESb is the Ewald sphere of blue light. Here, the helical axis direction AX of the cholesteric liquid crystal polymer layer is perpendicular to the film surface.

[0150] By adjusting the composition of each cholesteric liquid crystal polymer layer (the type and amount of the chiral dopant, and the birefringence of the liquid crystal monomer, etc.), the helical pitch of each cholesteric liquid crystal polymer layer and the birefringence of the liquid crystal are appropriately set, thereby, the optical band gap of each cholesteric polymer liquid crystal layer can be set to a desired value. Here, as an example, the wavelength of red light is set to 620nm, the wavelength of green light is set to 520nm, and the wavelength of blue light is set to 450nm for explanation.

[0151] The optical band gap width W is calculated by using the half pitch P / 2 and the extraordinary refractive index n of the liquid crystal of the cholesteric liquid crystal polymer layer. e , ordinary refractive index n o and the effective refractive index n eff , approximated by formula (1). The half pitch P / 2 is the length of the liquid crystal molecule's orientation direction rotated 180 degrees along the helical axis of the cholesteric liquid crystal polymer layer, which is half the helical pitch. The effective refractive index n eff The approximation is made by taking the volume average refractive index of the cholesteric liquid crystal polymer layer. The optical band gap width W is the refractive index n eff The size of the optical band gap in the wavenumber space.

[0152] [Mathematical formula 1]

[0153]

[0154] Using half pitch P / 2, wavelength λ of incident light, and effective refractive index n effThe Bragg condition is expressed by formula (2) where the incident angle θ is the angle between the helical axis and the wave number vector of the incident light. Here, the magnitude of the wave number vector of the incident light in the cholesteric liquid crystal polymer layer is n eff × 2π / λ. The direction of the wave number vector of the incident light is set to the traveling direction of the incident light.

[0155] [Mathematical formula 2]

[0156]

[0157] If the half pitch P of the cholesteric liquid crystal polymer layer is used for red light R / 2, abnormal refractive index n Re , ordinary refractive index n Ro and the effective refractive index n Reff , then the optical band gap width Wr of the optical band gap BGr of the cholesteric liquid crystal polymer layer for red light is expressed by formula (3).

[0158] [Mathematical formula 3]

[0159]

[0160] Similarly, if the half pitch P of the cholesteric liquid crystal polymer layer is used for green light G / 2, abnormal refractive index n Ge , ordinary refractive index n Go and the effective refractive index n Geff , then the optical band gap width Wg of the optical band gap BGg of the cholesteric liquid crystal polymer layer for green light is expressed by formula (4).

[0161] [Formula 4]

[0162]

[0163] Similarly, if the half pitch P of the cholesteric liquid crystal polymer layer used for blue light is B / 2, abnormal refractive index n Be , ordinary refractive index n Bo and the effective refractive index n Beff , then the optical band gap width Wb of the optical band gap BGb of the cholesteric liquid crystal polymer layer for blue light is expressed by formula (5).

[0164] [Mathematical formula 5]

[0165]

[0166] When Bragg reflection occurs in each cholesteric liquid crystal polymer layer, the wave number vector of the light changes to the Bragg wave number vector of each cholesteric liquid crystal polymer layer to become outgoing light. For example, the wave number vector Vir of the incident light of red light and the Bragg wave number vector Vwr of the cholesteric liquid crystal polymer layer for red light are synthesized to obtain the wave number vector Vor of the outgoing light of red light.

[0167] The magnitude of the Bragg wave number vector Vwr of the cholesteric liquid crystal polymer layer for red light is 4π / P R , and its direction is parallel to the helical axis direction AX. The magnitude of the Bragg wave number vector Vwg of the cholesteric liquid crystal polymer layer for green light is 4π / P G , and its direction is parallel to the helical axis direction AX. The magnitude of the Bragg wave number vector Vwb of the cholesteric liquid crystal polymer layer for blue light is 4π / P B , whose direction is parallel to the helical axis direction AX. For each combination of wavelength and cholesteric liquid crystal polymer layer, the number of absolute values ​​of the incident angle that satisfies the exact Bragg condition is 1 or 0.

[0168] However, the cholesteric liquid crystal polymer layer has a finite optical band gap width which is not 0. Accordingly, for the combination of incident angle and wavelength that satisfies the Bragg condition, Fig.21 Light in the region of the wave number space with a limited thickness shown in FIG. 1 (which is referred to as "light within the optical band gap") also causes Bragg reflection. On the other hand, according to the principle of wave number uncertainty, even if the material of the cholesteric liquid crystal polymer layer is narrow in the optical band gap width, if the film thickness of the cholesteric liquid crystal polymer layer is reduced, the uncertainty of the wave number can be increased and the region causing Bragg reflection can be expanded. However, in this case, the reflectivity of the Bragg reflection decreases, and the light passing through the cholesteric liquid crystal polymer layer increases. This method cannot be used for the notch filter 13, but can be used for a holographic combiner, etc., and is effective when it is desired to increase the transmittance.

[0169] That is, in the wave number space, incident light in a range where the optical band gap width relaxes the Bragg condition causes Bragg reflection. Fig.21 The reason why Bragg reflection occurs in a certain range of incident angles is shown in FIG. The change amount Dv of the wave number vector at this time is different from the Bragg wave number vector relative to the incident light that does not satisfy the Bragg condition, but is along the spiral axis direction AX when the spiral axis direction AX is perpendicular to the film surface of the cholesteric liquid crystal polymer layer. On the other hand, this is not the case when the spiral axis direction AX is inclined relative to the film surface of the cholesteric liquid crystal polymer layer.

[0170] like Fig. 22As shown, using the magnitude of the Bragg wave number vector 4π / P of the cholesteric liquid crystal polymer layer and the inclination angle α of the helical axis, the magnitude of the in-plane direction component of the Bragg wave number vector is represented by 4π×sinα / P. For example, the in-plane direction component VCr based on the Bragg wave number vector Vwr is represented by 4π×sinα / P R The wave number vector of the emitted light is determined so that the in-plane direction component of the Bragg wave number vector becomes the in-plane direction component of the variation of the wave number vector.

[0171] The effective refractive index n is calculated by the law of conservation of energy and by taking the volume average refractive index value of the cholesteric liquid crystal polymer layer as described above. eff By approximation, it can be approximated to the effective refractive index n eff It has nothing to do with the direction of the wave number vector. Therefore, the condition that the end points of the wave number vectors of the incident light and the outgoing light are located on the Ewald sphere can be added, and based on this condition and the condition of the in-plane directional component of the change in the wave number vector, the wave number vector of the outgoing light can be uniquely determined relative to the incident light.

[0172] In terms of the relationship between the wave number vector of the outgoing light and the wave number vector of the incident light, the magnitude of the wave number vector is actually the same as that of the surface relief diffraction grating of 4π×sinα / P. The above relationship is different from the surface relief diffraction grating in that only light within the optical band gap is diffracted, higher-order unnecessary diffraction is not easily generated, and only circularly polarized light of one polarity is diffracted.

[0173] The cholesteric liquid crystal produced for light of a long wavelength causes Bragg reflection with respect to light of a shorter wavelength only within a range of incident angles greater than the assumed long wavelength light. For example, within the incident angle range Rrg, the cholesteric liquid crystal polymer layer for red light causes Bragg reflection of green light. Within the incident angle range Rrb, the cholesteric liquid crystal polymer layer for red light causes Bragg reflection of blue light. Within the incident angle range Rgb, the cholesteric liquid crystal polymer layer for green light causes Bragg reflection of blue light. However, if the incident angle range designed so that the light of a shorter wavelength causes Bragg reflection does not overlap with the incident angle range Rf, it can be seen that there is no problem. The incident angle range Rf is the range of incident angles that acts as a notch filter with respect to all wavelengths of red light, green light, and blue light.

[0174] Here, the estimated incident angle range Rf is the incident angle in the cholesteric liquid crystal polymer layer which always has an effective refractive index of 1 or more, rather than the incident angle from the atmosphere. Light is incident on the cholesteric liquid crystal polymer layer from the atmosphere with refraction caused by the effective refractive index. Therefore, it can be seen that by using a cholesteric liquid crystal polymer having a large effective refractive index, a wider incident angle range from the atmosphere can be obtained.

[0175] In order to obtain a large incident angle range Rf of the notch filter 13, the helical axis direction AX of the cholesteric liquid crystal polymer layer is set so that the helical axis direction AX and the direction of the incident wave number vector when the light (light beam) at the center of the field of view reaches the center of the eye box and the light beam at the center of the light beam is incident on the notch filter 13 are as parallel as possible. In addition, on the basis of satisfying this condition, the setting angle of the notch filter 13 and the helical axis direction AX may be set so that the helical axis is perpendicular to the film surface.

[0176] Next, refer to Fig.23 and Fig.24 , the cholesteric liquid crystal polymer layer in the reflector 53 is described in detail. Fig.23 It is a diagram of the wave number space of light and the Ewald sphere of blue light and red light observed on a cross section including the wave number vector of the helical axis direction of the cholesteric liquid crystal polymer and the wave number vector of the center of the light beam that becomes the center of the field of view in the incident light. Here, the helical axis direction AX of the cholesteric liquid crystal polymer layer is inclined at an angle α relative to the film surface. In addition, Fig.23 and Fig.24 In the figure, for convenience of explanation, the same reference numerals are given to the elements corresponding to the cholesteric liquid crystal polymer layer of the notch filter 13, and repeated explanations are omitted.

[0177] Since red light and blue light of circularly polarized light of the same polarity are incident on the reflector 53, it is necessary to consider the wave number space of the red light and the blue light in which wavelength selectivity becomes a problem. As described above, the cholesteric liquid crystal produced for light of long wavelength causes Bragg reflection only in the range where the incident angle is larger than the assumed light of the above-mentioned long wavelength with respect to light of shorter wavelength. For example, within the incident angle range Rrb, the cholesteric liquid crystal polymer layer for red light performs Bragg reflection on blue light. However, if it is designed so that the incident angle range Rrb does not overlap with the incident angle range Rg1, it can be seen that there is no problem. The incident angle range Rg1 is the range of the incident angle that functions as a diffraction grating relative to the wavelength of the red light and the blue light.

[0178] Here, the estimated incident angle range Rg1 is the incident angle in the cholesteric liquid crystal polymer layer which always has an effective refractive index of 1 or more, rather than the incident angle from the atmosphere. Light is incident on the cholesteric liquid crystal polymer layer from the atmosphere with refraction caused by the effective refractive index. Therefore, it can be seen that by using a cholesteric liquid crystal polymer having a large effective refractive index, a larger incident angle range from the atmosphere can be obtained.

[0179] Since green light is circularly polarized light of a different polarity than red and blue light, wavelength selectivity is not an issue. Therefore, green light can be considered independently of red and blue light. Fig.24 As shown, the optical band gap width Wg of the cholesteric liquid crystal polymer layer for green light can also be expanded as much as possible.

[0180] In a holographic combiner, in order to realize the function of a concave mirror, it is necessary to change the required inclination α of the spiral axis and the in-plane direction of the inclination according to the location. The inclination α of the spiral axis and the in-plane direction of the inclination can be controlled by the orientation pattern of the optical orientation layer. In order to obtain a larger viewing angle, the spiral pitch can also be changed according to the location. For example, by utilizing the temperature dependence of the spiral pitch of the cholesteric liquid crystal and imparting an in-plane temperature distribution in the state before the cholesteric liquid crystal polymer layer is cured, the spiral pitch can be changed according to the location. It is also possible to use an inkjet method when applying the liquid crystal and change the chiral dopant concentration according to the location, thereby changing the spiral pitch according to the location. The change in the spiral pitch corresponds to the change in the magnitude of the Bragg wave number vector.

[0181] Furthermore, when the liquid crystal is applied by using an inkjet method, the composition of the liquid crystal monomer is changed for each cholesteric liquid crystal polymer layer and depending on the location, thereby controlling the magnitude of the birefringence of the liquid crystal monomer (here, the difference between the inverse of the ordinary refractive index and the inverse of the extraordinary refractive index). Thus, the width of the optical band gap can be controlled for each cholesteric liquid crystal polymer layer and depending on the location. Sometimes, it is necessary to control the optical band gap in conjunction with the control of the helical pitch.

[0182] When the incident angle with respect to the helical axis and the inclination α of the helical axis are substantially equal, light is vertically emitted from the hologram combiner. In this case, the incident angle with respect to the plane is approximately 2α.

[0183] It is desired that the diffraction angles of the three colors of light are consistent and chromatic aberration disappears. When the inclination α of the helical axis of the cholesteric liquid crystal polymer layer for red light constituting the hologram diffraction layer 56 is satisfied, R and the effective refractive index n Reff , the inclination α of the helical axis of the cholesteric liquid crystal polymer layer for green light constituting the holographic diffraction layer 55 G and the effective refractive index n Geff, the inclination α of the helical axis of the cholesteric liquid crystal polymer layer for blue light constituting the holographic diffraction layer 54 B and the effective refractive index n Beff , wavelength of red light λ R , wavelength of green light λ G , and the wavelength of blue light λ B In the case of the formula (6), the diffraction angles of the three colors of light are consistent.

[0184] [Mathematical formula 6]

[0185]

[0186] Since the diffraction angle of light when it emerges in the atmosphere is taken as an issue, the effective refractive index does not enter into formula (6). R and spiral pitch P R The exposure pattern of the photo-alignment layer of the cholesteric liquid crystal polymer layer is directly determined by red light. G and spiral pitch P G The slope α is directly determined by the exposure pattern of the photo-alignment layer of the cholesteric liquid crystal polymer layer for green light. B and spiral pitch P B The exposure pattern of the photo-alignment layer of the cholesteric liquid crystal polymer layer for blue light is directly determined. Therefore, chromatic aberration can be easily eliminated.

[0187] In the retinal projection device 1E, the same effect as that of the retinal projection device 1A is achieved with respect to the common structure with the retinal projection device 1A. In order to expand the eye box, it is necessary to expand the permissible range of the incident angle of the light beam incident on the optical unit 5A. If a broadband element with a large permissible range of the incident angle is used, the permissible range of the wavelength is expanded. Since the red wavelength and the green wavelength are close, and the green wavelength and the blue wavelength are close, if the permissible range of the wavelength is expanded, stray light caused by chromatic aberration may be generated. In contrast, in the retinal projection device 1E, the notch filter 13 extracts the left circularly polarized light in the red light Lr, extracts the right circularly polarized light in the green light Lg, and extracts the left circularly polarized light in the blue light Lb.

[0188] Since the hologram diffraction layer 54 reflects (scatters) left circularly polarized light, even if the permissible wavelength range of the hologram diffraction layer 54 is expanded, it is not easy to reflect the right circularly polarized light of the green light Lg. Similarly, since the hologram diffraction layer 55 reflects right circularly polarized light, even if the permissible wavelength range of the hologram diffraction layer 55 is expanded, it is not easy to reflect the left circularly polarized light of the red light Lr and the left circularly polarized light of the blue light Lb. Similarly, since the hologram diffraction layer 56 reflects left circularly polarized light, even if the permissible wavelength range of the hologram diffraction layer 56 is expanded, it is not easy to reflect the right circularly polarized light of the green light Lg. Since the red wavelength and the blue wavelength are separated, the hologram diffraction layers 54 and 56 can maintain wavelength selectivity. Therefore, the left circularly polarized light of the red light Lr is not easily reflected by the hologram diffraction layer 54, and the left circularly polarized light of the blue light Lb is not easily reflected by the hologram diffraction layer 56. Therefore, the possibility of generating stray light caused by chromatic aberration can be reduced.

[0189] If the torsion direction of the torsion structure of the electric field vector generated by the rotation of the electric field vector of the circularly polarized light at a certain moment and with the traveling direction of the light as the axis is consistent with the torsion direction of the torsion structure of the orientation direction of the liquid crystal molecules of the cholesteric liquid crystal polymer layer, and the incident light satisfies a certain condition, Bragg reflection is caused and the incident light is diffracted and reflected. On the other hand, if the above-mentioned torsion directions are opposite to each other, Bragg reflection is not caused and the incident light is transmitted. As described above, by adjusting the helical pitch (to be precise, the product of the helical pitch and the effective refractive index of the cholesteric liquid crystal polymer layer) of the helical structure composed of the liquid crystal molecules of the cholesteric liquid crystal polymer layer, the helical axis direction, the effective refractive index, the torsion direction, the extraordinary refractive index and the ordinary refractive index of each layer obtained by slicing the cholesteric liquid crystal polymer layer with a plane perpendicular to the helical axis, circularly polarized light of a desired polarization state of a desired wavelength is reflected.

[0190] In the retinal projection device 1E, the filter layer 32 is configured to reflect right circularly polarized light from the blue light Lb, the filter layer 33 is configured to reflect left circularly polarized light from the green light Lg, and the filter layer 34 is configured to reflect right circularly polarized light from the red light Lr. Therefore, the left circularly polarized light of the red light Lr, the right circularly polarized light of the green light Lg, and the left circularly polarized light of the blue light Lb can be extracted, and the function of the notch filter 13 can be realized.

[0191] The hologram diffraction layer 54 is configured to reflect the left circularly polarized light of the blue light Lb, the hologram diffraction layer 55 is configured to reflect the right circularly polarized light of the green light Lg, and the hologram diffraction layer 56 is configured to reflect the left circularly polarized light of the red light Lr. Therefore, the function of the reflector 53 can be realized.

[0192] In addition, the notch filter 13 may be configured to allow right circularly polarized light in the red light Lr to pass through and reflect left circularly polarized light, allow left circularly polarized light in the green light Lg to pass through and reflect right circularly polarized light, and allow right circularly polarized light in the blue light Lb to pass through and reflect left circularly polarized light. In this case, the optical device 5A is configured to scatter (reflect) right circularly polarized light in a wavelength range including red wavelengths, scatter (reflect) left circularly polarized light in a wavelength range including green wavelengths, and scatter (reflect) right circularly polarized light in a wavelength range including blue wavelengths.

[0193] Next, the manufacturing method of the cholesteric liquid crystal polymer layer (PVG) and PBOE is described. As an example of an azo dye used in the orientation layer, brilliant yellow (CAS RN: 3051-11-4, product code: B0783 Brilliant Yellow: Brilliant Yellow 3051-11-4, Tokyo Chemical Industry Co., Ltd.) can be cited. The solution obtained by dissolving brilliant yellow (BY) in dimethylformamide (DMF) is evenly applied to the transparent substrate 31 by spin coating and dried on a flat electric furnace. The brilliant yellow molecules are oriented by exposing the film thus obtained to the interference electric field of the desired circularly polarized light. Thus, an orientation layer is formed.

[0194] In the case of manufacturing PVG, a solution obtained by dissolving a reactive liquid crystal unit containing a chiral dopant and a photopolymerization initiator in a solvent such as toluene is applied to the alignment layer, and then the solvent is evaporated to form a thin film. In the case of manufacturing PBOE, the same as above is performed, but no chiral dopant is added. Thereafter, if the coordination of the liquid crystal is stable, the thin film is cured using UV light. In the case where the thickness of the thin film obtained by applying the solution once is insufficient, the above-mentioned coating and curing are repeated until an appropriate thickness is obtained. In the case of PBOE, the thickness is controlled to function as a half-wavelength plate.

[0195] In the exposure of the orientation layer, for example, an exposure device described in non-patent document 1 (Jianghao Xiong, Shin-Tson Wu, "Planar liquid crystal polarization optics for augmented reality and virtual reality: from fundamentals to applications", eLight1, Article number: 3, 2021) is used. In addition, as an example of a right-handed chiral dopant, R5011 (CAS NO.944537-61-5Chiral Dopant R5011, Daken Chemical Limited) can be cited. As an example of a left-handed chiral dopant, S5011 (CAS NO.693227-30-4Chiral Dopant S5011|Daken Chemical Limited) can be cited. As an example of a reactive liquid crystal unit, reactive liquid crystal unit RM257 (CAS RN: 174063-87-7, product code: B5356, Tokyo Chemical Industry Co., Ltd.) can be cited. By doping with a chiral dopant, a helical structure in a direction perpendicular to the plane can be easily realized. The periodicity can be controlled by adjusting the twisting force and concentration of the helix of the chiral dopant.

[0196] As a method of stacking a plurality of PVGs, there is the following method. After forming one PVG on the transparent substrate 31, an intermediate layer is applied on the liquid crystal layer of the PVG so that the influence of the orientation of the liquid crystal layer does not affect it. Then, the next PVG is formed on the intermediate layer. As another method of stacking a plurality of PVGs, after forming the PVG on another substrate, the PVGs may be stacked by sequentially repeating transfer based on bonding and peeling on the same transparent substrate 31.

[0197] In addition, the retinal projection device of the present invention is not limited to the above-mentioned embodiment.

[0198] PBOE44 can also be composed of metasurfaces.

[0199] The deflection element 41 can change the direction of travel of the light beam. The deflection element 41 can also be a reflector (mirror), for example. The deflection element 41 can also change the direction of travel of the light beam by controlling the wavefront using a spatial light modulator (SLM). Specifically, the deflection element 41 can also be a variable diffraction grating formed by a liquid crystal SLM.

[0200] (Note)

[0201] [Project 1]

[0202] A retinal projection device, wherein:

[0203] have:

[0204] A projector module including a laser module for emitting laser light, a collimating lens for converting the laser light into a parallel light beam, and a movable mirror for performing scanning using the light beam;

[0205] A projection lens that focuses the light beam emitted from the projector module at a focusing position;

[0206] an optical unit, which is arranged to overlap with the focus position and includes a deflection element for changing the traveling direction of the light beam;

[0207] An optical device, which converts the light beam into parallel light and irradiates the light beam toward the user's retina;

[0208] A controller that adjusts the traveling direction of the light beam based on the deflection element according to the position of the pupil of the user.

[0209] [Project 2]

[0210] The retinal projection device according to item 1, wherein:

[0211] It also includes: a first wave plate, which is disposed between the laser module and the deflection element and converts the linear polarization light into circular polarization light,

[0212] The above-mentioned deflection element has:

[0213] one or more second wavelength plates capable of switching between a state of preserving the polarization state of circularly polarized light and a state of converting the circularly polarized light into circularly polarized light of opposite polarity according to an applied voltage;

[0214] one or more Pancharatnam-Berry phase optical elements that convert circularly polarized light into circularly polarized light of opposite polarity and diffract the circularly polarized light in a diffraction direction corresponding to the polarity of the incident circularly polarized light,

[0215] The one or more second wave plates and the one or more Pancharatnam-Berry phase optical elements are alternately arranged one by one to form an array.

[0216] [Item 3]

[0217] The retinal projection device according to item 2, wherein:

[0218] The deflection element further includes a reflector for reflecting the circularly polarized light while preserving the polarity of the circularly polarized light.

[0219] The reflector is arranged at one end of the array body.

[0220] [Item 4]

[0221] The retinal projection device according to item 2 or item 3, wherein:

[0222] The one or more Pancharatnam-Berry phase optical elements are composed of liquid crystal polymers or metasurfaces.

[0223] [Item 5]

[0224] The retinal projection device according to any one of items 2 to 4, wherein:

[0225] The second wave plate includes a pair of transparent electrodes and a liquid crystal layer provided between the pair of transparent electrodes.

[0226] [Item 6]

[0227] The retinal projection device according to any one of items 1 to 5, wherein:

[0228] The invention further includes a wavefront correction unit for correcting aberration of a wavefront of light rays that pass through the pupil among the light rays constituting the light beam.

[0229] [Item 7]

[0230] The retinal projection device according to item 6, wherein:

[0231] The wavefront correction unit is composed of any one of LCOS, a liquid crystal lens, and a variable shape mirror.

[0232] [Item 8]

[0233] The retinal projection device according to any one of items 1 to 7, wherein:

[0234] The optical device further includes a focusing unit disposed between the optical unit and the optical device and focusing the light beam.

[0235] [Item 9]

[0236] The retinal projection device according to any one of items 1 to 8, wherein:

[0237] The laser module emits the laser light obtained by combining red laser light having a red wavelength, green laser light having a green wavelength, and blue laser light having a blue wavelength.

[0238] [Item 10]

[0239] The retinal projection device according to item 9, wherein:

[0240] The invention further comprises: a filter that allows the circularly polarized light of the first polarity in the light of the red wavelength to pass through and reflects the circularly polarized light of the second polarity different from the first polarity, allows the circularly polarized light of the second polarity in the light of the green wavelength to pass through and reflects the circularly polarized light of the first polarity, and allows the circularly polarized light of the first polarity in the light of the blue wavelength to pass through and reflects the circularly polarized light of the second polarity,

[0241] The above optical device is a holographic combiner,

[0242] The above optical device has:

[0243] a first holographic diffraction layer that diffracts the circularly polarized light of the first polarity in the first wavelength range including the red wavelength;

[0244] a second holographic diffraction layer that diffracts the circularly polarized light of the second polarity in a second wavelength range including the green wavelength;

[0245] The third holographic diffraction layer diffracts the circularly polarized light of the first polarity in a third wavelength range including the blue wavelength.

[0246] [Item 11]

[0247] The retinal projection device according to item 10, wherein:

[0248] The first holographic diffraction layer is composed of a cholesteric liquid crystal polymer layer having a helical structure, the helical structure having a helical pitch corresponding to the red wavelength and twisted in a twisting direction for reflecting the circularly polarized light of the first polarity,

[0249] The second holographic diffraction layer is composed of a cholesteric liquid crystal polymer layer having a helical structure, the helical structure having a helical pitch corresponding to the green wavelength and twisted in a twisting direction for reflecting the circularly polarized light of the second polarity,

[0250] The third holographic diffraction layer is composed of a cholesteric liquid crystal polymer layer having a helical structure, the helical structure having a helical pitch corresponding to the blue wavelength and twisted in a twisting direction for reflecting the circularly polarized light of the first polarity.

[0251] [Item 12]

[0252] The retinal projection device according to item 10 or item 11, wherein:

[0253] The above filter has:

[0254] A first filter layer, which is composed of a first cholesteric liquid crystal polymer layer having a helical structure, the helical structure having a helical pitch corresponding to the red wavelength and twisted in a twisting direction for reflecting the circularly polarized light of the second polarity;

[0255] A second filter layer, which is composed of a second cholesteric liquid crystal polymer layer having a helical structure, the helical structure having a helical pitch corresponding to the green wavelength and twisted in a twisting direction for reflecting the circularly polarized light of the first polarity;

[0256] The third filter layer is composed of a third cholesteric liquid crystal polymer layer having a helical structure having a helical pitch corresponding to the blue wavelength and twisted in a twisting direction for reflecting the circularly polarized light of the second polarity.

Claims

1. A retinal projection device, wherein: have: A projector module including a laser module for emitting laser light, a collimating lens for converting the laser light into a parallel light beam, and a movable mirror for performing scanning using the light beam; a projection lens that focuses the light beam emitted from the projector module at a focusing position; an optical unit, which is arranged to overlap with the focus position and includes a deflection element for changing the traveling direction of the light beam; An optical device that converts the light beam into parallel light and irradiates it toward the user's retina; and A controller adjusts the traveling direction of the light beam based on the deflection element according to the position of the user's pupil.

2. The retinal projection device according to claim 1, wherein: It also includes: a first wave plate, which is disposed between the laser module and the deflection element and converts the linear polarization light into circular polarization light, The deflection element comprises: one or more second wavelength plates capable of switching between a state of preserving the polarization state of circularly polarized light and a state of converting the circularly polarized light into circularly polarized light of opposite polarity according to an applied voltage; one or more Pancharatnam-Berry phase optical elements that convert circularly polarized light into circularly polarized light of opposite polarity and diffract the circularly polarized light in a diffraction direction corresponding to the polarity of the incident circularly polarized light, The one or more second wavelength plates and the one or more Pancharatnam-Berry phase optical elements are alternately arranged one by one to form an array.

3. The retinal projection device according to claim 2, wherein: The deflection element further includes a reflector that reflects the circularly polarized light while preserving the polarity of the circularly polarized light. The reflector is arranged at one end of the array body.

4. A retinal projection device according to claim 2 or 3, wherein: The one or more Pancharatnam-Berry phase optical elements are composed of liquid crystal polymers or metasurfaces.

5. The retinal projection device according to any one of claims 2 to 4, wherein: The second wave plate includes a pair of transparent electrodes and a liquid crystal layer provided between the pair of transparent electrodes.

6. The retinal projection device according to any one of claims 1 to 5, wherein: The invention further includes a wavefront correction unit that corrects aberration of a wavefront of light that passes through the pupil among the light rays constituting the light beam.

7. The retinal projection device according to claim 6, wherein: The wavefront correction unit is composed of any one of LCOS, a liquid crystal lens, and a variable shape mirror.

8. The retinal projection device according to any one of claims 1 to 7, wherein: The optical device further includes a focusing unit disposed between the optical unit and the optical device and focusing the light beam.

9. The retinal projection device according to any one of claims 1 to 8, wherein: The laser module emits the laser light obtained by combining red laser light having a red wavelength, green laser light having a green wavelength, and blue laser light having a blue wavelength.

10. The retinal projection device according to claim 9, wherein: The invention further comprises: a filter that allows circularly polarized light of a first polarity in the light of the red wavelength to pass through and reflects circularly polarized light of a second polarity different from the first polarity, allows circularly polarized light of the second polarity in the light of the green wavelength to pass through and reflects the circularly polarized light of the first polarity, and allows circularly polarized light of the first polarity in the light of the blue wavelength to pass through and reflects the circularly polarized light of the second polarity, The optical device is a holographic combiner, The optical device comprises: a first holographic diffraction layer that diffracts the circularly polarized light of the first polarity in a first wavelength range including the red wavelength; a second holographic diffraction layer that diffracts the second-polarity circularly polarized light in a second wavelength range including the green wavelength; and A third holographic diffraction layer diffracts the circularly polarized light of the first polarity in a third wavelength range including the blue wavelength.

11. The retinal projection device according to claim 10, wherein: The first holographic diffraction layer is composed of a cholesteric liquid crystal polymer layer having a helical structure, the helical structure having a helical pitch corresponding to the red wavelength and twisted in a twisting direction for reflecting the circularly polarized light of the first polarity, The second holographic diffraction layer is composed of a cholesteric liquid crystal polymer layer having a helical structure, the helical structure having a helical pitch corresponding to the green wavelength and twisted in a twisting direction for reflecting the circularly polarized light of the second polarity, The third holographic diffraction layer is composed of a cholesteric liquid crystal polymer layer having a helical structure, the helical structure having a helical pitch corresponding to the blue wavelength and being twisted in a twisting direction for reflecting the circularly polarized light of the first polarity.

12. A retinal projection device according to claim 10 or 11, wherein: The filter has: a first filter layer composed of a first cholesteric liquid crystal polymer layer having a helical structure having a helical pitch corresponding to the red wavelength and twisted in a twisting direction for reflecting the second polarity circularly polarized light; a second filter layer composed of a second cholesteric liquid crystal polymer layer having a helical structure having a helical pitch corresponding to the green wavelength and twisted in a twisting direction for reflecting the circularly polarized light of the first polarity; and The third filter layer is composed of a third cholesteric liquid crystal polymer layer having a helical structure having a helical pitch corresponding to the blue wavelength and twisted in a twisting direction for reflecting the second polarity circularly polarized light.

Images