Retinal projection device

Abstract

To expand an eye box.SOLUTION: A retinal projection device 1 comprises: a projector module 2 that includes a laser module 21 for emitting laser light, a collimation lens 22 for converting laser light into parallel beams, and a movable mirror 23 for performing scanning by the beams; a projection lens 3 for converging the beams emitted from the projector module 2 at a convergence position; an optical unit 4 located so as to overlap the convergence position and including a deflection element 41 for changing a traveling direction of the beams; an optical device 5 for converting the beams into parallel rays of light and irradiating a retina of a user with these parallel rays of light; and a controller 10 for adjusting the traveling direction of the beams by the deflection element 41 in accordance with a pupil of the user.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to retinal projection devices. [Background technology]

[0002] 2. Description of the Related Art Retinal projection devices that directly project an image onto a user's retina are known (see, for example, Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] US Patent Application Publication No. 2019 / 0361250 [Patent Document 2] Patent Publication No. 2021-5072 [Patent Document 3] International Publication No. 2019 / 146367 [Non-patent literature]

[0004] [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 Summary of the Invention [Problem to be solved by the invention]

[0005] In the retinal projection devices described in Patent Documents 1 to 3, there is a risk that the image cannot be correctly recognized when the user moves his / her eyes. In this technical field, it is desired to expand the movable range of the eyes (eye box) in which the entire image can be correctly recognized.

[0006] The present disclosure describes a retinal projection device with expandable eyebox. [Means for solving the problem]

[0007] A retinal projection device according to one aspect of the present disclosure includes a projector module including a laser module that emits laser light, a collimation lens that converts the laser light into a parallel beam, and a movable mirror for scanning with the beam, a projection lens that focuses the beam emitted from the projector module at a focusing position, an optical unit arranged to overlap the focusing position and including a deflection element that changes the direction of the beam, an optical device that converts the beam into parallel light and irradiates it onto a user's retina, and a controller that adjusts the direction of the beam by the deflection element according to the position of the user's pupil.

[0008] In this retinal projection device, an optical unit including a deflection element is arranged so as to overlap with the focal position, and the direction of the beam is adjusted by the deflection element according to the position of the user's pupil. With this configuration, even if the user moves his / her eye, the direction of the beam can be changed following the movement of the user's pupil. Since the deflection element is arranged near the focal position, spherical aberration caused by the change in the direction of the beam (deflection) is reduced. Therefore, the quality of the image formed on the retina is maintained, and the user can correctly recognize the image. As a result, the eyebox can be expanded.

[0009] In some embodiments, the retinal projection device may further include a first wave plate provided between the laser module and the deflection element, which converts linearly polarized light into circularly polarized light. The deflection element may include one or more second wave plates capable of switching between a state in which the polarization state of the circularly polarized light is preserved and a state in which the circularly polarized light is converted into circularly polarized light of the opposite polarity, depending on an applied voltage, and one or more Pancharatnam-Berry phase optical elements that convert the circularly polarized light into circularly polarized light of the opposite polarity and diffract the circularly polarized light in a diffraction direction depending on the polarity of the incident circularly polarized light. The one or more second wave plates and the one or more Pancharatnam-Berry phase optical elements may be arranged alternately one by one to form an array. According to this configuration, the polarity (polarization state) of the circularly polarized light passing through the second wave plate can be switched by switching the second wave plate between a state in which the polarization state of the circularly polarized light is preserved and a state in which the circularly polarized light is converted into circularly polarized light of the opposite polarity. The diffraction direction in the Pancharatnam-Berry phase optical element provided behind the second wave plate is determined depending on the polarity of the circularly polarized light. Therefore, the traveling direction of the beam can be changed by applying a voltage to the second wave plate.

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

[0011] In some embodiments, the one or more Pancharatnam-Berry phase elements may be formed using a liquid crystal polymer or a metasurface, which can facilitate the formation of the Pancharatnam-Berry phase elements.

[0012] In some embodiments, the second wave plate may include a pair of transparent electrodes and a liquid crystal layer provided 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 in the direction of the electric field. Therefore, in a state in which a voltage is applied between the pair of transparent electrodes, the second wave plate preserves the polarization state of the circularly polarized light passing through the second wave plate. In a state in which 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 orientation state. At this time, the second wave plate converts the circularly polarized light passing through the second wave plate into circularly polarized light of the opposite polarity. In this way, depending on the presence or absence of a voltage applied between the pair of transparent electrodes, it is possible to switch between a state in which the polarization state of the circularly polarized light is preserved and a state in which the circularly polarized light is converted into circularly polarized light of the opposite polarity.

[0013] In some embodiments, the retinal projection device may further include a wavefront correction unit that corrects aberrations in the wavefront of light rays that pass through the pupil among the light rays that constitute the beam, thereby improving the resolution at the center of the visual field.

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

[0015] In some embodiments, the retinal projection device may further include a focusing unit disposed between the optical unit and the optical device to focus the beam. In this case, the optical unit can be disposed at a position away from the optical device. Therefore, the degree of freedom of the arrangement of the optical unit can be improved.

[0016] In some embodiments, the laser module may emit 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, thereby realizing a full-color retinal projection device.

[0017] In some embodiments, the retinal projection device may further include a filter that passes circularly polarized light of a first polarity in red wavelengths and reflects circularly polarized light of a second polarity different from the first polarity, passes circularly polarized light of a second polarity in green wavelengths and reflects circularly polarized light of the first polarity, and passes circularly polarized light of a first polarity in blue wavelengths and reflects circularly polarized light of the second polarity. The optical device may be a holographic combiner. The optical device may include a first holographic diffractive layer that diffracts circularly polarized light of a first polarity in a first wavelength range including red wavelengths, a second holographic diffractive layer that diffracts circularly polarized light of a second polarity in a second wavelength range including green wavelengths, and a third holographic diffractive layer that diffracts circularly polarized light of a first polarity in a third wavelength range including blue wavelengths.

[0018] In order to expand the eyebox, it is necessary to widen the allowable range of the incidence angle of the beam entering the holographic combiner. If a broadband element with a large allowable range of incidence angle is used, the allowable range of wavelengths will be widened. In this case, stray light due to chromatic aberration may occur. In response to this, the filter extracts circularly polarized light of the first polarity from the light of the red wavelength, circularly polarized light of the second polarity from the light of the green wavelength, and circularly polarized light of the first polarity from the light of the blue wavelength. Since the first holographic diffraction layer diffracts circularly polarized light of the first polarity, even if the allowable range of wavelengths of the first holographic diffraction layer is widened, circularly polarized light of the second polarity having a green wavelength is difficult to diffract. Similarly, since the second holographic diffraction layer diffracts circularly polarized light of the second polarity, circularly polarized light of the first polarity having a red wavelength and circularly polarized light of the first polarity having a blue wavelength are difficult to diffract even if the allowable range of wavelengths of the second holographic diffraction layer is widened. Similarly, since the third holographic diffractive layer diffracts circularly polarized light of the first polarity, even if the wavelength tolerance range of the third holographic diffractive layer is expanded, circularly polarized light of the second polarity having green wavelengths is less likely to be diffracted, thereby reducing the possibility of stray light due to chromatic aberration.

[0019] In some embodiments, the first holographic diffractive layer may be comprised of a cholesteric liquid crystal polymer layer having a helical structure with a helical pitch corresponding to a red wavelength and a twist direction that reflects circularly polarized light of a first polarity. The second holographic diffractive layer may be comprised of a cholesteric liquid crystal polymer layer having a helical structure with a helical pitch corresponding to a green wavelength and a twist direction that reflects circularly polarized light of a second polarity. The third holographic diffractive layer may be comprised of a cholesteric liquid crystal polymer layer having a helical structure with a helical pitch corresponding to a blue wavelength and a twist direction that reflects circularly polarized light of a first polarity.

[0020] When the twist direction of the twist structure of the electric field vector with the light traveling direction as the axis at a certain time, which is generated by the rotation of the electric field vector of the circularly polarized light, coincides with the twist direction of the twist structure of the liquid crystal molecule orientation direction of the cholesteric liquid crystal polymer layer, and the incident light satisfies a certain condition, Bragg reflection occurs and the incident light is diffracted and reflected. On the other hand, if the above twist directions are opposite to each other, the incident light is transmitted without Bragg reflection. The first holographic diffraction layer is configured to reflect circularly polarized light of a red wavelength with a first polarity, the second holographic diffraction layer is configured to reflect circularly polarized light of a green wavelength with a second polarity, and the third holographic diffraction layer is configured to reflect circularly polarized light of a blue wavelength with a first polarity. Thus, the above functions of the optical device can be realized.

[0021] In some embodiments, the filter may include a first filter layer made of a first cholesteric liquid crystal polymer layer having a helical structure with a helical pitch corresponding to a red wavelength and a helical structure with a twist direction that reflects circularly polarized light of a second polarity, a second filter layer made of a second cholesteric liquid crystal polymer layer having a helical structure with a helical pitch corresponding to a green wavelength and a helical structure with a twist direction that reflects circularly polarized light of the first polarity, and a third filter layer made of a third cholesteric liquid crystal polymer layer having a helical structure with a helical pitch corresponding to a blue wavelength and a helical structure with a twist direction that reflects circularly polarized light of the second polarity.

[0022] When the twist direction of the twist structure of the electric field vector with the light traveling direction as the axis at a certain time, which is generated by the rotation of the electric field vector of the circularly polarized light, coincides with the twist direction of the twist structure of the liquid crystal molecule orientation direction of the cholesteric liquid crystal polymer layer, and the incident light satisfies a certain condition, Bragg reflection occurs and the incident light is diffracted and reflected. On the other hand, if the above twist directions are opposite to each other, the incident light is transmitted without Bragg reflection. 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, it is possible to extract circularly polarized light of the first polarity of red wavelength, circularly polarized light of the second polarity of green wavelength, and circularly polarized light of the first polarity of blue wavelength, and the above function of the filter can be realized. Effect of the Invention

[0023] According to the aspects and embodiments of the present disclosure, the eyebox can be expanded. [Brief description of the drawings]

[0024] [Figure 1] FIG. 1 is a diagram showing the basic configuration of a retinal projection device according to an embodiment. [Diagram 2] FIG. 2 is a diagram illustrating a schematic configuration of the deflection element shown in FIG. [Diagram 3] FIG. 3 is a diagram illustrating a schematic configuration of the wave plate shown in FIG. [Figure 4] FIG. 4 is a diagram illustrating a schematic configuration of the Pancharatnam-Berry phase optical element shown in FIG. [Diagram 5] FIG. 5 is a cross-sectional view taken along line VV in FIG. [Figure 6] FIG. 6 is a diagram for explaining the operation of the deflection element shown in FIG. [Figure 7] FIG. 7 is a diagram for explaining the operation of the deflection element shown in FIG. [Figure 8] FIG. 8 is a diagram for explaining the operation of the deflection element shown in FIG. [Figure 9] FIG. 9 is a diagram for explaining the operation of the deflection element shown in FIG. [Figure 10] FIG. 10 is a diagram for explaining a change in wave vector due to deflection. [Figure 11] FIG. 11 is a diagram for explaining a case where the focusing position differs depending on the axial direction. [Figure 12] FIG. 12 is a diagram showing the basic configuration of a retinal projection device according to a modified example. [Figure 13] FIG. 13 is a diagram showing an application example of the retinal projection device shown in FIG. [Figure 14] FIG. 14 is a diagram showing another application example of the retinal projection device shown in FIG. [Figure 15] FIG. 15 is a diagram showing yet another application example of the retinal projection device shown in FIG. [Figure 16] FIG. 16 is a diagram showing yet another application example of the retinal projection device shown in FIG. [Figure 17] FIG. 17 is a diagram illustrating a schematic configuration of the deflection element shown in FIG. [Figure 18] FIG. 18 is a diagram for explaining the operation of the deflection element shown in FIG. [Figure 19] FIG. 19 is a diagram showing yet another application example of the retinal projection device shown in FIG. [Figure 20] FIG. 20 is a diagram illustrating a schematic configuration of the notch filter illustrated in FIG. [Figure 21] FIG. 21 is a diagram for explaining the principle of the notch filter shown in FIG. [Figure 22] FIG. 22 is a diagram for explaining the principle of the notch filter shown in FIG. [Figure 23] FIG. 23 is a diagram for explaining the principle of the reflector shown in FIG. [Figure 24] FIG. 24 is a diagram for explaining the principle of the reflector shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the drawings. In the description of the drawings, the same elements are given the same reference numerals, and duplicated descriptions are omitted. An XYZ coordinate system may be shown in each drawing. The Y-axis direction is a direction that intersects (for example, perpendicular to) the X-axis direction and the Z-axis direction. The Z-axis direction is a direction that intersects (for example, perpendicular to) the X-axis direction and the Y-axis direction.

[0026] A retinal projection device according to an embodiment will be described with reference to FIG. 1. FIG. 1 is a diagram showing a basic configuration of a retinal projection device according to an embodiment. The retinal projection device 1 shown in FIG. 1 is a device that directly projects (draws) an image onto a user's retina. The retinal projection device 1 is mounted on, for example, 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.

[0027] The projector module 2 is a module that performs scanning with a beam, and includes a laser module 21, a collimation lens 22, a movable mirror 23, and a wave plate 26 (first wave plate).

[0028] The laser module 21 emits laser light of a color and intensity corresponding to the pixels of an image projected onto the retina. For example, a full-color laser module is used as the laser module 21. In this case, the laser module 21 includes a red laser diode, a green laser diode, a blue laser diode, and a multiplexer that multiplexes the laser light emitted from each laser diode into one laser light. For example, a planar lightwave circuit (PLC) is used as the multiplexer. The laser module 21 emits laser light obtained by multiplexing 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.

[0029] The collimation lens 22 is an optical element that converts the laser light emitted from the laser module 21 into a parallel beam. The movable mirror 23 is a member for performing scanning with the beam converted by the collimation lens 22. The movable mirror 23 is provided in the emission direction of the beam converted by the collimation lens 22. As the movable mirror 23, for example, a MEMS (Micro Electro Mechanical Systems) mirror is used.

[0030] The wave plate 26 is an optical element that converts linearly polarized light into circularly polarized light. Since the laser module 21 generally emits linearly polarized light, it is necessary to convert the linearly polarized light into circularly polarized light before the light reaches a Pancharatnam-Berry phase optical element 44 (described later) in the optical unit 4. For this reason, the wave plate 26 is disposed between the laser module 21 and the optical unit 4. The wave plate 26 may be disposed immediately after the collimation lens 22, for example. When an element that is assumed to operate with linearly polarized light is disposed between the laser module 21 and the optical unit 4, the wave plate 26 is disposed in a stage subsequent to the element that is assumed to operate with linearly polarized light. As the wave plate 26, a true ¼ wave plate is used in consideration of wavelength dispersion, etc., but a ¼+N (N is a natural number) wave plate may also be used.

[0031] 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 .

[0032] The projection lens 3 is an optical element that focuses the beam emitted from the projector module 2 at a focusing position P. The focusing position P is the position where the beam focuses in a cross section including the central axis of the beam. When the beam focuses to one point, the focusing position P is an intermediate imaging plane. For the sake of simplicity, a case where the focusing position P is an intermediate imaging plane will be illustrated here.

[0033] The optical unit 4 is a unit for changing the traveling direction of the 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 may also be expressed as the direction of the pupil PP or the direction of the line of sight. The optical unit 4 is disposed so as to overlap with the focal 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 beam. The deflection element 41 will be described in detail later.

[0034] The optical device 5 is an optical element that converts the beam into parallel light and irradiates the light on the user's retina. The optical device 5 may be an eyepiece or a combiner.

[0035] The controller 10 is a device that performs overall control of the retinal projection device 1. The controller 10 adjusts the traveling direction of the beam by the deflection element 41 according to the position of the user's pupil PP. For example, the controller 10 adjusts the traveling direction of the beam by changing the voltage applied to the deflection element 41. The retinal projection device 1 may further include a detection unit (not shown) that detects the position of the pupil PP. In FIG. 1, positions EP1 and EP2 are illustrated as examples of the position of the pupil PP.

[0036] Next, the deflection element 41 will be described in detail with reference to Figs. 2 to 5. Fig. 2 is a diagram that shows a schematic configuration of the deflection element shown in Fig. 1. Fig. 3 is a diagram that shows a schematic configuration of the wave plate shown in Fig. 2. Fig. 4 is a diagram that shows a schematic configuration of the Pancharatnam-Berry phase optical element (hereinafter, sometimes referred to as "PBOE") shown in Fig. 2. Fig. 5 is a cross-sectional view taken along line VV in Fig. 4.

[0037] 2, the deflection element 41 is a transmissive deflection element and includes one or more wave plates 43 (second wave plates) and one or more PBOEs 44. The number of wave plates 43 included in the deflection element 41 is the same as the number of PBOEs 44 included in the deflection element 41.

[0038] Wave plate 43 is an optical element that can switch between a state in which the polarization state (polarity) of circularly polarized light passing through wave plate 43 is preserved (maintained) and a state in which the circularly polarized light passing through wave plate 43 is converted into circularly polarized light of the opposite polarity, depending on a voltage applied to wave plate 43. Wave plate 43 has, for example, a rectangular plate shape. As shown in FIG. 3, wave plate 43 includes transparent substrate 431, transparent substrate 432, transparent electrode 433, transparent electrode 434, alignment layer 435, alignment layer 436, and liquid crystal layer 437.

[0039] Each of the transparent substrate 431 and the transparent substrate 432 is a substrate having visible light transmissivity that transmits visible light. The transparent substrate 431 and the transparent substrate 432 are made of a material having a small birefringence. Examples of materials for the transparent substrate 431 and the transparent substrate 432 include SiO2, optical glass, and a glass substrate for liquid crystal displays. The transparent substrate 431 and the transparent substrate 432 are disposed substantially parallel to each other and spaced apart from each other in the Z-axis direction. The transparent substrate 431 has a surface 431a and a surface 431b that intersect (here, perpendicular to) the Z-axis direction. The transparent substrate 432 has a surface 432a and a surface 432b that intersect (here, perpendicular to) the Z-axis direction. The surface 431a and the surface 432a face each other in the Z-axis direction. The surface 431b is the surface opposite to the surface 431a. The surface 432b is the surface opposite to the surface 432a.

[0040] Each of the transparent electrode 433 and the transparent electrode 434 (a pair of transparent electrodes) is an electrode that is conductive and has visible light transmissivity that transmits visible light. An example of a constituent material of the transparent electrode 433 and the transparent electrode 434 is ITO. The transparent electrode 433 and the transparent electrode 434 face each other in the Z-axis direction with the liquid crystal layer 437 interposed therebetween. 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.

[0041] The alignment layer 435 and the alignment layer 436 are layers for controlling the arrangement (alignment) of the liquid crystal molecules Lm1 contained 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.

[0042] 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. An example of a material constituting the liquid crystal layer 437 is a nematic liquid crystal. The alignment of the liquid crystal molecules Lm1 is controlled in response to an electric field applied to the liquid crystal layer 437, and the optical characteristics of the liquid crystal layer 437 change.

[0043] In the wave plate 43, the beam enters the transparent substrate 431 from 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 that order, and exits from surface 432b.

[0044] Since the liquid crystal material is in contact with the alignment layers 435 and 436, the liquid crystal molecules Lm1 are in an in-plane alignment state when no voltage is applied between the transparent electrodes 433 and 434 (voltage non-applied state). That is, the slow axis of the liquid crystal molecules Lm1 is substantially parallel to the plane of the alignment layers 435 and 436 with which the liquid crystal layer 437 is in contact. At this time, the length (thickness) in the Z-axis direction of the liquid crystal layer 437 is adjusted so that the wave plate 43 functions as a half wave plate (that is, it converts circularly polarized light passing through the wave plate 43 into circularly polarized light of the opposite polarity).

[0045] When a voltage is applied between the transparent electrodes 433 and 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 molecules Lm1 is substantially perpendicular to the surfaces of the alignment layers 435 and 436 with which the liquid crystal layer 437 is in contact. Therefore, in a state in which a voltage is applied between the transparent electrodes 433 and 434 (voltage applied state), the wave plate 43 preserves the polarization state of the circularly polarized light passing through the wave plate 43.

[0046] The PBOE 44 is an optical element that converts circularly polarized light passing through the PBOE 44 into circularly polarized light of the opposite polarity, and diffracts the circularly polarized light in a diffraction direction according to the polarity of the circularly polarized light incident on the PBOE 44. The PBOE 44 has, for example, a rectangular plate shape. As shown in Figures 4 and 5, the PBOE 44 includes a transparent substrate 441, an alignment layer 442, and a liquid crystal layer 443 (liquid crystal polymer).

[0047] The transparent substrate 441 is a substrate having visible light transmissivity that transmits visible light. The transparent substrate 441 is made of a material having low birefringence as well as surface accuracy. Examples of materials for the transparent substrate 441 include SiO2, optical glass, and glass substrates for liquid crystal displays. The transparent substrate 441 has a surface 441a and a surface 441b that intersect (here, perpendicular to) the Z-axis direction.

[0048] The alignment layer 442 is a layer for controlling the arrangement (alignment) of the liquid crystal molecules Lm2 contained in the liquid crystal layer 443. The alignment layer 442 is provided on the surface 441a. An example of a constituent material of the alignment layer 442 is a material whose molecular alignment changes when irradiated with polarized light.

[0049] The liquid crystal layer 443 is provided on the alignment layer 442. Examples of materials for the liquid crystal layer 443 include nematic liquid crystal and cholesteric liquid crystal. The liquid crystal layer 443 is made of a liquid crystal polymer obtained by aligning liquid crystal molecules using photopolymerizable liquid crystal molecules and then polymerizing the liquid crystal molecules. The method for producing the PBOE 44 will be described in detail later.

[0050] The liquid crystal molecules Lm2 included in the liquid crystal layer 443 are three-dimensionally arranged in the X-axis direction, the Y-axis direction, and the Z-axis direction. In the X-axis direction, for example, the liquid crystal molecules Lm2 are arranged so that the angle (orientation angle) between the slow axis of the liquid crystal molecule Lm2 and the X-axis direction gradually increases or decreases. Specifically, in the X-axis direction, the liquid crystal molecules Lm2 are arranged so that the orientation angle gradually increases from 0 degrees to 180 degrees within a range corresponding to the period T of the diffraction grating. In the Y-axis direction and the Z-axis direction, the liquid crystal molecules Lm2 are arranged so that the orientation angles of the liquid crystal molecules Lm2 are the same. Since the phase changes by -360 degrees, that is, one wavelength, with a rotation of the orientation angle of 180 degrees, the rotation of the orientation angle of 180 degrees corresponds to one period T of the diffraction grating.

[0051] With the above configuration, the PBOE 44 functions as a diffraction grating that diffracts circularly polarized light at a certain 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 alignment layer 442, and the liquid crystal layer 443 in this order. At this time, the circularly polarized light is gradually changed to circularly polarized light of the opposite polarity due to the birefringence of the liquid crystal molecules Lm2 contained in the liquid crystal layer 443. The relative phase of the circularly polarized light of the opposite polarity to the incident circularly polarized light at that time changes depending on the alignment angle of the liquid crystal molecules Lm2, and the amount of change is equal to -2 times the amount of change in the alignment angle of the liquid crystal molecules Lm2 (where the rotation direction of the electric field vector of the incident circularly polarized light is considered to be positive). However, the alignment angle and phase angle are considered in radians. This allows the circularly polarized light of the opposite polarity to have a phase difference that depends on the passing position. In other words, since it is possible to generate a tilt in the wavefront, the PBOE 44 functions as a diffraction grating. The diffraction directions of left-handed circularly polarized light (circularly polarized light of a first polarity) and right-handed circularly polarized light (circularly polarized light of a second polarity) are opposite. When the deflection element 41 includes a plurality of PBOEs 44, the diffraction angles of the PBOEs 44 may be different from one another.

[0052] The length (thickness) of the liquid crystal layer 443 in the Z-axis direction is set so that the phase difference due to the birefringence of the liquid crystal is 180 degrees, that is, the PBOE 44 functions as a half-wave plate whose slow axis changes in the in-plane direction. This allows the diffraction efficiency to reach nearly 100%. In this case, there is almost no zero-order (straight light). The PBOE 44 does not generate second-order or higher-order diffracted light either.

[0053] Wave plates 43 and PBOEs 44 are alternately arranged one by one in the Z-axis direction to form an array 42. The array 42 has a first end 42a and a second end 42b which are opposite ends in the Z-axis direction. A wave plate 43 is arranged at the first end 42a, and a PBOE 44 is arranged at the second end 42b. When the deflection element 41 is arranged near the intermediate image plane, among the PBOEs 44 included in the deflection element 41, the PBOE 44 closest to the intermediate image plane may be configured to have a function as a field lens.

[0054] Next, beam steering (beam deflection) by the deflection element 41 will be described with reference to Fig. 6 to Fig. 9. Fig. 6 to Fig. 9 are diagrams for explaining the operation of the deflection element shown in Fig. 2. For convenience of explanation, a case will be illustrated in which the deflection element 41 includes two wave plates 43 and two PBOEs 44, and a left-handed circularly polarized beam Bin is incident on the deflection element 41. The diffraction angle on the left side (upper side of the paper in Fig. 6 to Fig. 9) with respect to the incident direction of the beam Bin is set to a positive value.

[0055] In the following explanation, it is assumed that the diffraction angle of PBOE44 does not depend on the angle of incidence on PBOE44. This assumption is valid as a good approximation when the diffraction angle of PBOE44 is small. In reality, in PBOE44, the in-plane component of the wave vector of incident light changes due to diffraction by an intrinsic wave vector in 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 angle of incidence. Therefore, the additivity of the diffraction of PBOE44 described above does not strictly apply to the angle, but actually applies to the change in the in-plane component of the wave vector of circularly polarized light due to diffraction.

[0056] 6, both of the two wave plates 43 are set to a voltage applied state. In this case, when the beam Bin is incident on the first wave plate 43, the left-handed circularly polarized beam B1 is emitted from the first wave plate 43 and incident on the first PBOE 44. Then, the right-handed circularly polarized beam B2 is emitted from the first PBOE 44 at a diffraction angle θ1 in the diffraction direction corresponding to the left-handed circularly polarized light (the upper side of the paper in FIG. 6) and incident on the second wave plate 43.

[0057] Then, right-handed circularly polarized beam B3 is emitted from the second wave plate 43 and enters the second PBOE 44. Then, left-handed circularly polarized beam Bout is emitted from the second PBOE 44 at a diffraction angle θ2 in the diffraction direction (lower side of the paper in FIG. 6) according to the right-handed circularly polarized light. Therefore, beam Bout is emitted at a diffraction angle (θ1-θ2) with respect to the incident direction of beam Bin. Note that in this example, diffraction angle θ2 is larger than diffraction angle θ1.

[0058] 7, the first wave plate 43 is set to a voltage-unapplied state, and the second wave plate 43 is set to a voltage-applied state. In this case, when the beam Bin is incident on the first wave plate 43, a right-handed circularly polarized beam B1 is emitted from the first wave plate 43 and incident on the first PBOE 44. Then, a left-handed circularly polarized beam B2 is emitted from the first PBOE 44 at a diffraction angle θ1 in the diffraction direction corresponding to the right-handed circularly polarized light (the lower side of the paper in FIG. 7) and incident on the second wave plate 43.

[0059] Then, left-handed circularly polarized beam B3 is emitted from the second wave plate 43 and enters the second PBOE 44. Then, right-handed circularly polarized beam Bout is emitted from the second PBOE 44 at a diffraction angle θ2 in the diffraction direction (upper side of the paper in FIG. 7) according to the left-handed circularly polarized light. Therefore, beam Bout is emitted at a diffraction angle (θ2-θ1) with respect to the incident direction of beam Bin.

[0060] 8, the first wave plate 43 is set to a voltage applied state, and the second wave plate 43 is set to a voltage not applied state. In this case, when the beam Bin is incident on the first wave plate 43, a left-handed circularly polarized beam B1 is emitted from the first wave plate 43 and incident on the first PBOE 44. Then, a right-handed circularly polarized beam B2 is emitted from the first PBOE 44 at a diffraction angle θ1 in the diffraction direction corresponding to the left-handed circularly polarized light (the upper side of the paper in FIG. 8) and incident on the second wave plate 43.

[0061] Then, left-handed circularly polarized beam B3 is emitted from the second wave plate 43 and enters the second PBOE 44. Then, right-handed circularly polarized beam Bout is emitted from the second PBOE 44 at a diffraction angle θ2 in the diffraction direction according to the left-handed circularly polarized light. Therefore, beam Bout is emitted at a diffraction angle (θ1+θ2) with respect to the incident direction of beam Bin.

[0062] 9, both of the two wave plates 43 are set to a voltage non-applied state. In this case, when the beam Bin is incident on the first wave plate 43, a right-handed circularly polarized beam B1 is emitted from the first wave plate 43 and incident on the first PBOE 44. Then, a left-handed circularly polarized beam B2 is emitted from the first PBOE 44 at a diffraction angle θ1 in the diffraction direction corresponding to the right-handed circularly polarized light (the lower side of the paper in FIG. 9) and incident on the second wave plate 43.

[0063] Then, right-handed circularly polarized beam B3 is emitted from the second wave plate 43 and enters the second PBOE 44. Then, left-handed circularly polarized beam Bout is emitted from the second PBOE 44 at a diffraction angle θ2 in the diffraction direction according to the right-handed circularly polarized light. Therefore, beam Bout is emitted at a diffraction angle (-θ1-θ2) with respect to the incident direction of beam Bin.

[0064] In this way, the traveling direction of the beam passing through the deflection element 41 is changed by switching the state of each wave plate 43 between a voltage applied state and a voltage non-applied state. The traveling direction of the beam passing through the deflection element 41 is determined by the number n of pairs of wave plates 43 and PBOEs 44 included in the optical unit 4, and is expressed as follows: n The direction of travel can be switched as follows.

[0065] Next, the effect of the retinal projection device 1 will be described with reference to FIG. 10. FIG. 10 is a diagram for explaining the change in wave vector due to deflection. As shown in FIG. 10, when deflection is performed at a position away from the focusing position P, focusing at a (virtual) focusing point generated when the deflected beam is extended forward and backward in the traveling axis direction becomes incomplete, and spherical aberration occurs. This is because the optical system arranged at the subsequent stage is designed to finally convert the light diverging from the focusing point into parallel light, and if the focusing is incomplete, the conversion to parallel light is also incomplete. Here, this is expressed as "spherical aberration". On the other hand, when deflection is performed at the focusing position P, the spherical aberration is reduced.

[0066] In the retinal projection device 1 described above, the optical unit 4 including the deflection element 41 is arranged so as to overlap with the focal position P, and the beam direction by the deflection element 41 is adjusted according to the position of the user's pupil PP. With this configuration, even if the user moves his / her eyes, the beam direction can be changed following the movement of the user's pupil PP. Since the deflection element 41 is arranged near the focal position P, spherical aberration caused by the change in the beam direction (deflection) is reduced. Therefore, the quality of the image formed on the retina is maintained, and the user can correctly recognize the image. As a result, the eyebox can be expanded.

[0067] The polarity (polarization state) of the circularly polarized light passing through the wave plate 43 can be switched by switching the wave plate 43 between a state in which the polarization state of the circularly polarized light is preserved (voltage not applied state) and a state in which the circularly polarized light is converted into circularly polarized light of the opposite polarity (voltage applied state). The diffraction direction in the PBOE 44 provided after the wave plate 43 is determined according to the polarity of the circularly polarized light. Therefore, depending on the voltage applied to each wave plate 43, it becomes possible to select the traveling direction of the beam from among the number of traveling directions according to the number n of pairs of wave plates 43 and PBOE 44 included in the optical unit 4.

[0068] In the wave plate 43, a liquid crystal layer 437 is provided between the transparent substrate 431 and the transparent substrate 432. According to this configuration, 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 in which a voltage is applied between the transparent substrate 431 and the transparent substrate 432, the wave plate 43 preserves the polarization state of the circularly polarized light passing through the wave plate 43. In a state in which no voltage is 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 wave plate 43 converts the circularly polarized light passing through the wave plate 43 into circularly polarized light of the opposite polarity. In this way, depending on the presence or absence of a voltage applied between the transparent substrate 431 and the transparent substrate 432, it is possible to switch between a state in which the polarization state of the circularly polarized light is preserved and a state in which the circularly polarized light is converted into circularly polarized light of the opposite polarity.

[0069] The PBOE 44 is made of a liquid crystal polymer, which makes it easy to form the PBOE 44.

[0070] The projector module 2 emits a laser beam obtained by multiplexing a red laser beam, a green laser beam, and a blue laser beam, thereby realizing a full-color retinal projection device 1.

[0071] In the examples shown in Figs. 6 to 9, each PBOE 44 is diffractable in the X-axis direction. This configuration makes it possible to follow a change in the viewpoint in the X-axis direction. In order to follow a change in the viewpoint in the Y-axis direction, the deflection element 41 may include a PBOE 44 that is diffractable in the Y-axis direction. The deflection element 41 may include a PBOE 44 that is diffractable in the X-axis direction and a PBOE 44 that is diffractable in the Y-axis direction. In this case, two-dimensional beam steering in the XY plane is realized.

[0072] 11, when a Keplerian optical system in which the magnification in the X-axis direction is different from the magnification in the Y-axis direction is used as the projection lens 3, no intermediate image plane is formed. In this case, the focusing position Px where the beam focuses in the X-axis direction is separated from the focusing position Py where the beam focuses in the Y-axis direction. The focusing positions Px form a linear set extending in the Y-axis direction. The focusing positions Py form a linear set extending in the X-axis direction.

[0073] The farther the position of the deflection element 41 is from the focusing position, the larger the aberration of the wavefront due to the deflection becomes. Therefore, the deflection element 41 capable of diffraction in the X-axis direction may be provided at the focusing position Px, and the deflection element 41 capable of diffraction in the Y-axis direction may be provided at the focusing position Py. In other words, the optical unit 4 may include a deflection element 41 provided at the focusing position Px and capable of diffraction in the X-axis direction, and a deflection element 41 provided at the focusing position Py and capable of diffraction in the Y-axis direction. According to this configuration, the position of the deflection element 41 capable of diffraction in the X-axis direction is brought closer to the focusing position Px, and the position of the deflection element 41 capable of diffraction in the Y-axis direction is brought closer to the focusing position Py. Therefore, the aberration of the wavefront due to the deflection can be suppressed, and the cost required for correcting the aberration can be reduced.

[0074] Next, a configuration capable of tracking changes in the viewpoint in the Z-axis direction (front-back direction) will be described with reference to Fig. 12. Fig. 12 is a diagram showing the basic configuration of a retinal projection device according to a modified example. As shown in Fig. 12, the retinal projection device 1 according to the modified example is mainly different from the retinal projection device 1 of the above embodiment in that the optical unit 4 further includes a deflection element 45.

[0075] Deflection element 45 differs from deflection element 41 mainly in that it includes a PBOE 44 functioning as a concave-convex lens instead of the PBOE 44 functioning as a diffraction grating that diffracts light at a constant diffraction angle. As a method for determining the orientation of liquid crystal molecule Lm2 to realize such a PBOE 44, for example, the following method is used.

[0076] Generally, the lens function corresponds to the amount of phase shift before and after the passage of a light beam at each in-plane position. On the other hand, in PBOE44, the polarity of the circularly polarized light is inverted by the transmission of the light beam, and the direction of rotation of the electric field vector is inverted. Specifically, the electric field vector obtained by reflecting the electric field vector of the incident circularly polarized light with respect to an axis perpendicular to the slow axis determined by 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 amount of phase shift before and after the passage of the light beam at each in-plane position corresponds to -2 times the amount of rotation of the orientation azimuth angle of the liquid crystal molecule Lm2 in the in-plane direction (the polarity of the rotation direction is positive in the rotation direction of the electric field vector of the incident circularly polarized light). 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 is inevitably determined by the required lens function. According to this concept, for example, a PBOE that functions as a convex lens when the incident light is right-circularly polarized is designed by arranging the liquid crystal molecule Lm2 so that the orientation azimuth angle rotates to the right as one moves from the center to the periphery when viewed from the incident surface.

[0077] For example, the PBOE 44 functions as a convex lens for right-handed circularly polarized light and a concave lens for left-handed circularly polarized light. The multiple PBOEs 44 included in the deflection element 45 are configured to have different focal lengths, making it possible to accommodate multiple viewpoint positions in the Z-axis direction. In FIG. 12, positions EP3 and EP4 are illustrated as examples of the positions of the pupil PP.

[0078] The retinal projection device 1 according to the modified example also has the same effects as the retinal projection device 1 according to the above embodiment with respect to the configuration common to the retinal projection device 1 according to the above embodiment. In the retinal projection device 1 according to the modified example, the optical unit 4 includes a deflection element 45, so that it is possible to follow a change in the viewpoint in the Z-axis direction. In other words, even if the distance between the optical device 5 and the user's pupil PP varies, the field of view can be secured. For example, when the retinal projection device 1 is applied to a near-eye display such as smart glasses, it is possible to tolerate a deviation in the wearing position of the near-eye display.

[0079] Next, an application example of the retinal projection device will be described with reference to Fig. 13. Fig. 13 is a diagram showing an application example of the retinal projection device shown in Fig. 1. The retinal projection device 1A shown in Fig. 13 can be applied to a near-eye display such as smart glasses. Note that in Fig. 13, the controller 10 is omitted.

[0080] 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 transmissivity that transmits visible light. Examples of materials constituting the transparent substrate 51 include SiO2, optical glass, and optical plastic. The transparent substrate 51 has a surface 51a facing the eyeball E of a user wearing the near-eye display. The transparent substrate 51 may 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, for example, a reflective diffraction grating layer such as a polarization-dependent volume grating (PVG).

[0081] The projector module 2 further includes a wavefront correction lens 24 (wavefront correction unit). The wavefront correction lens 24 is a lens that corrects wavefront aberration of light rays (light rays corresponding to the center of the field of view) that pass through the pupil PP among the light rays that make up the beam. The wavefront correction lens 24 corrects, for example, third-order or higher aberrations. The wavefront correction lens 24 is provided between the collimation lens 22 and the movable mirror 23. The wavefront correction lens 24 is provided, for example, in front of the movable mirror 23. The wavefront correction lens 24 is composed of a liquid crystal lens.

[0082] In the wavefront compensation 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 that corresponds to the center of the visual field when the pupil PP is located at position EP1. The light ray Rc2 is a light ray that corresponds to the center of the visual field when the pupil PP is located at position EP2. Therefore, the wavefront compensation lens 24 adaptively corrects the wavefront aberration according to the position of the pupil PP. Specifically, the controller 10 (see FIG. 1) controls the wavefront compensation lens 24 according to the position of the user's pupil PP so that the wavefront error of the beam that constitutes a pixel on the line of sight, i.e., in the direction of the gaze point, among the beams that pass through the pupil PP, is minimized.

[0083] The optical unit 4 further includes a field lens 46. The field lens 46 is a lens that changes the traveling direction of a light ray near the focal point of the beam. The field lens 46 is provided at the second end 42b (output end) of the array 42. Specifically, the field lens 46 is provided so as to cover the PBOE 44 located at the second end 42b.

[0084] The retinal projection device 1A further includes a wave plate 9 (first wave plate) instead of the wave plate 26. The wave plate 9 is an optical element that converts linearly polarized light into circularly polarized light. The wave plate 9 is disposed between the laser module 21 and the optical unit 4. When an element that is premised on operating with linearly polarized light is disposed between the laser module 21 and the optical unit 4, the wave plate 9 is disposed after the element that is premised on operating with linearly polarized light. As the wave plate 9, a true ¼ wave plate is used in consideration of wavelength dispersion, etc., but a ¼+N (N is a natural number) wave plate may also be used.

[0085] The retinal projection device 1A further includes a relay lens 6 (focusing section) and a wavefront correction lens 7 (wavefront correction section). The relay lens 6 is a lens that focuses the 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 convex lens or a group of lenses that function as a convex lens.

[0086] The wavefront correction lens 7 is a lens that mainly corrects the field angle dependency of the focus of the beam, i.e., the field angle dependency of the diopter on the retina, fluctuations caused by switching of the deflection element 41. The wavefront correction lens 7 is provided between the projection lens 3 and the optical unit 4. The wavefront correction lens 7 is provided, for example, immediately after the projection lens 3. The wavefront correction lens 7 may be provided immediately before the projection lens 3. The wavefront correction lens 7 is formed of a liquid crystal lens.

[0087] 13, the wavefront aberration of each of the light rays Rc1 and Rc2 is corrected. Note that, like the wavefront compensation lens 24, the wavefront compensation lens 7 is configured to adaptively correct the wavefront aberration according to the position of the pupil PP.

[0088] The retinal projection device 1A also achieves the same effects as the retinal projection device 1 with respect to the configuration 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 visual field can be improved. The wavefront correction lens 7 and the wavefront correction lens 24 are made of a liquid crystal lens. The wavefront correction lens 7 and the wavefront correction lens 24 can be easily realized by using a liquid crystal lens. When a liquid crystal lens is used, since most liquid crystal lenses function for linearly polarized light rather than circularly polarized light, a waveplate that converts linearly polarized light into circularly polarized light is placed between the liquid crystal lens and the optical unit 4.

[0089] The wavefront correction lens 7 mainly corrects the variation due to the switching of the deflection element 41 in the field angle dependency of the focus of the beam, that is, the field angle dependency of the diopter on the retina. The role of the wavefront correction lens 7 is to correct the change in the image formation position on the retina (whether in front of or behind the retina) depending on the angle of incidence on the pupil PP. This variation occurs due to the variation in the aberration of the optical system of the retina projection device 1 due to the switching of the deflection element 41, or due to the aberration of the naked eye. In particular, the wavefront correction lens 7 can deal with the type of myopia in which the eye axis is elongated, in which the focus of the naked eye is likely to shift to the rear of the retina at the periphery of the field of view compared to the center of the field of view. This correction can be made with fixed function lenses such as ordinary progressive power glasses, but the correction is not appropriate when the line of sight moves up, down, left, or right, so the effect of the correction is small. On the other hand, the wavefront correction lens 7 can make correction in response to the movement of the line of sight by using a variable lens such as a liquid crystal lens.

[0090] A variable wavefront compensation lens 24 is provided between the collimation lens 22 and the movable mirror 23. As a result, as shown in FIG. 13, third-order or higher aberrations caused by the beam being obliquely incident on an optical element such as the combiner 5 can be effectively compensated for. Although the aberrations depend on the angle and position of the beam, the wavefront compensation function of the wavefront compensation lens 24 may be set so as to provide the best compensation for the beam at an angle and position that coincides with the line of sight when it is incident on the pupil PP. In this case, no practical problem occurs because the resolution of the naked eye is low except for a very narrow range around the line of sight. To this end, the controller 10 detects the position and angle of the pupil PP, and controls the beam to reach the position of the pupil PP by deflection by the optical unit 4, and controls the wavefront compensation lens 24 to maintain high resolution at the center of the visual field of the naked eye.

[0091] The retina projection device 1 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. Furthermore, the controller 10 controls the wavefront correction lens 24 so that the best correction is applied to the beam that forms the pixel at the center of the visual field of the naked eye, i.e., the gaze 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, it is possible to completely apply wavefront correction to all beams, and focus adjustment can also be performed for each beam. In this case, the wavefront correction lens 24 can also include the function of the wavefront correction lens 7, so that the wavefront correction lens 7 can be omitted.

[0092] As long as the spatial separation of beams with different angles of view is well maintained at the position of the wavefront compensation lens 7, the wavefront compensation lens 7 may be provided downstream of the deflection element 41, immediately before or immediately after the relay lens 6. In this case, an element (wave plate) that converts the circularly polarized light from the deflection element 41 into appropriate linearly polarized light is provided upstream. When the wavefront compensation lens 7 is provided downstream of the deflection element 41, the waveplate 9 may be provided between the wavefront compensation lens 24 and the optical unit 4, or may be provided immediately after the collimation lens 22.

[0093] The focal point FP of the optical device 5 is located in front of the optical device 5. Therefore, if the relay lens 6 is not provided, the optical unit 4 needs to be disposed at the focal point FP. In this case, there is a risk that the optical unit 4 will block the user's field of vision. 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 configuration, the optical unit 4 can be disposed at a position away from the optical device 5. Therefore, the degree of freedom in the arrangement of the optical unit 4 can be improved, and the user's field of vision can be ensured.

[0094] Next, another application example of the retinal projection device will be described with reference to FIG. 14. FIG. 14 is a diagram showing another application example of the retinal projection device shown in FIG. 1. The retinal projection device 1B shown in FIG. 14 is mainly different from the retinal projection device 1A in that the reflector 52 is a concave mirror instead of a reflective diffraction grating layer, that it does not include a wavefront correction lens 7, and that the projector module 2 includes a wave plate 26 instead of the wave plate 9. The retinal projection device 1B can be applied to near-eye displays such as smart glasses. Note that the controller 10 is not shown in FIG. 14.

[0095] In the retinal projection device 1B, the same effects as those of the retinal projection device 1A can be achieved with respect to the configuration common to the retinal projection device 1A. In the retinal projection device 1B, the reflector 52 is a concave mirror. A concave mirror causes less focus fluctuation due to switching of the deflection element 41 than a holographic combiner. In the retinal projection device 1B, the projector module 2 includes a wavefront correction lens 24. The wavefront correction lens 24 adaptively corrects wavefront aberration according to the position of the pupil PP, thereby further improving the resolution at the center of the visual field. The wavefront correction lens 24 is made of a liquid crystal lens. The wavefront correction lens 24 can be easily realized by using a liquid crystal lens.

[0096] Next, with reference to FIG. 15, a further application example of the retinal projection device will be described. FIG. 15 is a diagram showing a further application example of the retinal projection device shown in FIG. 1. The retinal projection device 1C shown in FIG. 15 differs from the retinal projection device 1B mainly in that the projector module 2 includes a reflective wavefront compensation element 25 (wavefront compensation unit) instead of the wavefront compensation lens 24. The retinal projection device 1C can be applied to near-eye displays such as smart glasses. Note that the controller 10 is omitted from FIG. 15.

[0097] The wavefront compensation element 25 is an optical element that compensates for wavefront aberration of a ray (a ray corresponding to the center of the visual field) that passes through the pupil PP among the rays that constitute the beam. The wavefront compensation element 25 compensates for, for example, third-order or higher aberration. The wavefront compensation element 25 reflects the beam emitted from the collimation lens 22 and irradiates it on the movable mirror 23. The wavefront compensation element 25 is, for example, composed of a deformable mirror. Examples of the deformable mirror include a MEMS type deformable mirror and a piezoelectric element type deformable mirror. The wavefront compensation element 25 may be composed of an LCOS.

[0098] In the retinal projection device 1C, the configuration common to retinal projection device 1B achieves the same effects as in retinal projection device 1B. In retinal projection device 1C, projector module 2 includes a wavefront compensation element 25. Wavefront compensation element 25 adaptively compensates for wavefront aberration according to the position of pupil PP, thereby further improving the resolution at the center of the visual field. Wavefront compensation element 25 is composed of a deformable mirror or LCOS. By using a deformable mirror or LCOS, wavefront compensation element 25 can be easily realized.

[0099] Next, with reference to Figs. 16 to 18, another application example of the retinal projection device will be described. Fig. 16 is a diagram showing another application example of the retinal projection device shown in Fig. 1. Fig. 17 is a diagram showing a schematic configuration of the deflection element shown in Fig. 16. Fig. 18 is a diagram for explaining the operation of the deflection element shown in Fig. 16. The retinal projection device 1D shown in Fig. 16 is mainly different 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 a near-eye display such as smart glasses. Note that the controller 10 is omitted from Fig. 16.

[0100] 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 beam emitted from the projection lens 3 and reflects the beam emitted from the optical unit 4A.

[0101] The optical unit 4A differs from the optical unit 4 mainly in that it includes a deflection element 41A instead of the deflection element 41, and in the arrangement of the field lens 46. The field lens 46 is provided at the first end 42a. Specifically, the field lens 46 is provided so as to cover the wave plate 43 located at the first end 42a. The deflection element 41A is a reflective deflection element.

[0102] As shown in FIG. 17, the deflection element 41A is mainly different from the deflection element 41 in that it further includes a reflector 47. The reflector 47 is an optical element that reflects circularly polarized light while preserving (maintaining) the polarity of the circularly polarized light. The reflector 47 is called a Handedness Preserving Mirror (HPM). The reflector 47 is provided at the second end 42b (one end) of the array 42. Specifically, the reflector 47 is superimposed on the PBOE 44 located at the second end 42b. An example of the reflector 47 is a Polarization Preserving Anisotropic Mirror (PPAM). The PPAM is formed by alternately laminating a plurality of films having in-plane birefringence and a thickness of approximately ¼ wavelength with their slow axes perpendicular to each other. The reflector 47 may be formed by superimposing a ¼ wavelength plate on the mirror surface of a normal mirror.

[0103] Beam steering (beam deflection) by the deflection element 41A will be described with reference to Fig. 18. For convenience of explanation, a case will be illustrated in which the deflection element 41A includes two wave plates 43 and two PBOEs 44, and a right-handed circularly polarized beam Bin is incident on the deflection element 41A. In the example shown in Fig. 18, both of the two wave plates 43 are set to a voltage applied state.

[0104] In this case, when beam Bin is incident on the first wave plate 43, right-handed circularly polarized beam B1 is emitted from the first wave plate 43 and enters the first PBOE 44. Then, left-handed circularly polarized beam B2 is emitted from the first PBOE 44 at a diffraction angle θ1 in the diffraction direction corresponding to the right-handed circularly polarized light (upper side of the paper in FIG. 18) and enters the second wave plate 43. Then, left-handed circularly polarized beam B3 is emitted from the second wave plate 43 and enters the second PBOE 44. Then, right-handed circularly polarized beam B4 is emitted from the second PBOE 44 at a diffraction angle θ2 in the diffraction direction corresponding to the left-handed circularly polarized light (lower side of the paper in FIG. 18).

[0105] Then, the beam B4 is reflected by the reflector 47 while maintaining its polarization state, and is emitted from the reflector 47 as a beam B5 and enters the second PBOE 44. Then, the left-handed circularly polarized beam B6 is emitted from the second PBOE 44 at a diffraction angle θ2 in the diffraction direction (the lower side of the paper in FIG. 18) according to the right-handed circularly polarized light, and enters the second wave plate 43. Then, the left-handed circularly polarized beam B7 is emitted from the second wave plate 43 and enters the first PBOE 44. Then, the right-handed circularly polarized beam B8 is emitted from the first PBOE 44 at a diffraction angle θ1 in the diffraction direction (the upper side of the paper in FIG. 18) according to the left-handed circularly polarized light, and enters the first wave plate 43. Then, the right-handed circularly polarized beam Bout is emitted from the first wave plate 43.

[0106] Therefore, beam Bout is emitted in a direction opposite to the incident direction of beam Bin at a diffraction angle of (2×θ1−2×θ2). In this example, diffraction angle θ1 is larger than diffraction angle θ2. Thus, in deflection element 41A, the beam passes through the same PBOE 44 twice. Therefore, the amount of change in the wave vector caused by deflection element 41A is twice the amount of change in the wave vector caused by deflection element 41.

[0107] In the above explanation, it is assumed that the diffraction angle of PBOE44 does not depend on the angle of incidence to PBOE44. This assumption is valid as a good approximation when the diffraction angle of PBOE44 is small. In reality, in PBOE44, the in-plane component of the wave vector of the incident light changes by an intrinsic wave vector in the in-plane direction determined by the orientation pattern of the liquid crystal layer 443 of PBOE44 due to diffraction, and this change does not depend on the angle of incidence. Therefore, the additivity of the diffraction of PBOE44 described above does not strictly apply to the angle, but actually applies to the change in the in-plane component of the wave vector of the circularly polarized light due to diffraction. In other words, to be precise, in the above reflective deflection element 41A, the change in the in-plane component of the wave vector is doubled.

[0108] In the retina projection device 1D, the beam emitted from the projection lens 3 passes through the beam splitter 8 and enters the optical unit 4A, where it is deflected. The beam emitted from the optical unit 4A is then reflected by the beam splitter 8 and enters the optical device 5 via the relay lens 6.

[0109] When the deflection element 41A is disposed near the intermediate image plane, the PBOE 44 included in the deflection element 41A that is closer to the intermediate image plane may be configured to have a field lens function. In this case, the optical unit 4A does not need to include the field lens 46.

[0110] In the retinal projection device 1D, the same effects as those of the retinal projection device 1A can be achieved with respect to the components common to the retinal projection device 1A. If a reflector that inverts the circularly polarized light is provided at the second end 42b, the deflection obtained when the beam passes through the array 42 from the first end 42a to the second end 42b is offset by the deflection obtained when the beam passes through the array 42 from the second end 42b to 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 42.

[0111] With this configuration, a beam that has passed through array 42 from first end 42a to second end 42b is reflected by reflector 47 while preserving its polarization state, and passes through array 42 again from second end 42b to first end 42a. In deflection element 41A, a beam with the same polarization state passes through the same PBOE 44 twice, so that the amount of change in the in-plane component of the wave vector caused by deflection element 41A is twice the amount of change in the in-plane component of the wave vector caused by deflection element 41.

[0112] Next, with reference to Figs. 19 and 20, another application example of the retinal projection device will be described. Fig. 19 is a diagram showing another application example of the retinal projection device shown in Fig. 1. Fig. 20 is a diagram showing a schematic configuration of a notch filter shown in Fig. 19. The retinal projection device 1E shown in Fig. 19 is mainly different from the retinal projection device 1A in that it includes an optical device 5A instead of the optical device 5, and further includes a neutral density filter 11, a wave plate 12, and a notch filter 13. The retinal projection device 1E can be applied to near-eye displays such as smart glasses. Note that the controller 10 is omitted from Fig. 19.

[0113] The neutral density filter 11 is a filter for attenuating the light reflected by the notch filter 13. Stray light can be reduced by the neutral density filter 11. The wave plate 12 is an optical element that converts the polarization state of the beam output from the optical unit 4 from circularly polarized light to linearly polarized light. The wave plate 12 is, for example, a quarter wave plate. Instead of the wave plate 12, an absorptive linear polarizer may be used.

[0114] The notch filter 13 is a circular polarization dependent notch filter, and is a filter for removing unnecessary circularly polarized components from each of red wavelength light (hereinafter sometimes referred to as "red light Lr"), green wavelength light (hereinafter sometimes referred to as "green light Lg"), and blue wavelength light (hereinafter sometimes referred to as "blue light Lb"), and extracting desired circularly polarized components. The notch filter 13 has a function of passing left circularly polarized light of the red light Lr and reflecting right circularly polarized light, passing right circularly polarized light of the green light Lg and reflecting left circularly polarized light, and passing left circularly polarized light of the blue light Lb and reflecting right circularly polarized light.

[0115] As shown in FIG. 20, 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).

[0116] The transparent substrate 31 is a substrate having visible light transmissivity that transmits visible light. The transparent substrate 31 is made of a material having small birefringence. Examples of materials for the transparent substrate 31 include SiO2, optical glass, and glass substrates for liquid crystal displays. The transparent substrate 31 has a surface 31a and a surface 31b. The surface 31b is the surface opposite to the surface 31a.

[0117] The filter layer 32 is a layer that reflects right-handed circularly polarized light from the blue light Lb to remove right-handed circularly polarized light and extract left-handed circularly polarized light. The filter layer 32 is provided on the surface 31a. The filter layer 32 is a cholesteric liquid crystal polymer layer, and is PVG. The cholesteric liquid crystal polymer layer of the filter layer 32 has a helical pitch corresponding to the blue wavelength and has a helical structure in a twisted direction that reflects right-handed circularly polarized light. It is desirable that the direction of the helical axis is parallel to the direction of the central ray of the beam that arrives at the center of the field of view and the center of the pupil PP when the line of sight is directed forward. Note that the "direction of the helical axis" means the direction in which the helical axis extends, and will be referred to as the "helical axis direction" in the following description. The "twist direction" refers to the direction of twist in the sense of whether it is a right-handed screw or a left-handed screw.

[0118] The filter layer 33 is a layer that reflects left-handed circularly polarized light from the green light Lg to remove the left-handed circularly polarized light and extracts the right-handed 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 and is made of PVG. The cholesteric liquid crystal polymer layer of the filter layer 33 has a helical pitch corresponding to the green wavelength and has a helical structure with a twist direction that reflects left-handed circularly polarized light.

[0119] The filter layer 34 is a layer that reflects right-handed circularly polarized light from the red light Lr to remove the right-handed circularly polarized light and extract the left-handed 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 and is made of PVG. The cholesteric liquid crystal polymer layer of the filter layer 34 has a helical pitch corresponding to the red wavelength and has a helical structure with a twist direction that reflects right-handed circularly polarized light.

[0120] The optical device 5A is a holographic combiner. In this embodiment, the optical device 5A has a function of scattering left-handed circularly polarized light in a wavelength range (first wavelength range) including red wavelengths, scattering right-handed circularly polarized light in a wavelength range (second wavelength range) including green wavelengths, and scattering left-handed circularly polarized light in a wavelength range (third wavelength range) including blue wavelengths. The optical device 5A is mainly different from the optical device 5 in that it includes a reflector 53 instead of the reflector 52.

[0121] Similar to the reflector 52, the reflector 53 is provided on the surface 51a and functions as a semi-transparent concave mirror. The reflector 53 includes a holographic diffraction layer 54 (a third holographic diffraction layer), a holographic diffraction layer 55 (a second holographic diffraction layer), and a holographic diffraction layer 56 (a first holographic diffraction layer).

[0122] The holographic diffraction layer 54 is a reflective diffraction grating layer that scatters (reflects) left-handed circularly polarized light in a wavelength range that includes blue wavelengths. The holographic diffraction layer 54 does not scatter right-handed circularly polarized light in the above wavelength range. The holographic diffraction layer 54 is composed of a cholesteric liquid crystal polymer layer that has a helical pitch corresponding to blue wavelengths and a helical structure with a twist direction that reflects left-handed circularly polarized light.

[0123] The holographic diffraction layer 55 is a reflective diffraction grating layer that scatters (reflects) right-handed circularly polarized light in a wavelength range including the green wavelength. The holographic diffraction layer 55 is laminated on the holographic diffraction layer 54. The holographic diffraction layer 55 does not scatter left-handed 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 pitch corresponding to the green wavelength and a helical structure in a twisted direction that reflects right-handed circularly polarized light.

[0124] The holographic diffraction layer 56 is a reflective diffraction grating layer that scatters (reflects) left-handed circularly polarized light in a wavelength range that includes red wavelengths. The holographic diffraction layer 56 does not scatter right-handed circularly polarized light in the above wavelength range. The holographic diffraction layer 56 is composed of a cholesteric liquid crystal polymer layer that has a helical pitch corresponding to red wavelengths and a helical structure with a twist direction that reflects left-handed circularly polarized light.

[0125] The holographic diffraction layer 54, the holographic diffraction layer 55, and the holographic diffraction layer 56 are laminated in this order on the surface 51a. Specifically, the holographic diffraction layer 54 is provided on the surface 51a. The holographic diffraction layer 55 is laminated on the holographic diffraction layer 54. The holographic diffraction layer 56 is laminated on the holographic diffraction layer 55. The lamination order of the holographic diffraction layer 54, the holographic diffraction layer 55, and the holographic diffraction layer 56 may be arbitrarily changed.

[0126] Here, the cholesteric liquid crystal polymer layer in the notch filter 13 will be described in detail with reference to Fig. 21 and Fig. 22. Fig. 21 is a diagram showing the Ewald spheres of each color in the wave number space of light, viewed in a cross section including the wave number vector in the direction of the helical axis of the cholesteric liquid crystal polymer layer and the wave number vector of the center of the beam that is the center of the field of view of the incident light. The Ewald sphere ESr is the Ewald sphere of red light. The Ewald sphere ESg is the Ewald sphere of green light. The 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.

[0127] By adjusting the composition of each cholesteric liquid crystal polymer layer (the type and amount of 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 can be appropriately set, so that the optical band gap of each cholesteric polymer liquid crystal layer can be set to a desired value. As an example, the wavelength of red light is 620 nm, the wavelength of green light is 520 nm, and the wavelength of blue light is 450 nm.

[0128] The optical band gap width W is determined by the half pitch P / 2 and the extraordinary refractive index n of the liquid crystal in the cholesteric liquid crystal polymer layer. e , ordinary refractive index n o and the effective refractive index n eff The half pitch P / 2 is the length by which the alignment direction of the liquid crystal molecules rotates 180 degrees along the helical axis of the cholesteric liquid crystal polymer layer, and is half the helical pitch. The effective refractive index n eff is approximated by the volume-averaged refractive index of the cholesteric liquid crystal polymer layer. The optical band gap width W is the refractive index n eff is the size of the optical band gap in wavenumber space.

number

[0129] Half pitch P / 2, wavelength of incident light λ, effective refractive index n effUsing the angle of incidence θ, the Bragg condition is expressed by equation (2). The angle of incidence θ is the angle between the helical axis and the wave vector of the incident light. Here, the magnitude of the wave vector of the incident light in the cholesteric liquid crystal polymer layer is n eff × 2π / λ. The direction of the wave vector of the incident light is the propagation direction of the incident light.

number

[0130] Half-pitch P of cholesteric liquid crystal polymer layer for red light R / 2, extraordinary refractive index n Re , ordinary refractive index n Ro and the effective refractive index n Reff Using the formula (3), 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 the formula (3).

number

[0131] Similarly, the half pitch P of the cholesteric liquid crystal polymer layer for green light G / 2, extraordinary refractive index n Ge , ordinary refractive index n Go and the effective refractive index n Geff Using the formula (4), 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 the formula (4).

number

[0132] Similarly, the half pitch P of the cholesteric liquid crystal polymer layer for blue light B / 2, extraordinary refractive index n Be , ordinary refractive index n Bo and the effective refractive index n Beff Using the formula (5), the optical band gap width Wb of the optical band gap BGb of the blue light cholesteric liquid crystal polymer layer is expressed by the formula (5).

number

[0133] When each cholesteric liquid crystal polymer layer causes Bragg reflection, the wave vector of the light changes by the Bragg wave vector of each cholesteric liquid crystal polymer layer to become the outgoing light. For example, by combining the wave vector Vir of the incoming red light and the Bragg wave vector Vwr of the cholesteric liquid crystal polymer layer for red light, the wave vector Vor of the outgoing red light is obtained.

[0134] The magnitude of the Bragg wave vector Vwr of a cholesteric liquid crystal polymer layer for red light is 4π / P R The direction of the helical axis AX is parallel to the helical axis direction. The magnitude of the Bragg wave vector Vwg of the green light cholesteric liquid crystal polymer layer is 4π / P G The direction of the helical axis AX is parallel to the helical axis direction. The magnitude of the Bragg wave vector Vwb of the blue light cholesteric liquid crystal polymer layer is 4π / P B The direction of the helical axis AX is parallel to the helical axis AX. The number of absolute values ​​of the incident angles that satisfy the exact Bragg condition is 1 or 0 for each combination of wavelength and cholesteric liquid crystal polymer layer.

[0135] However, the cholesteric liquid crystal polymer layer has a finite optical band gap width that is not 0. Accordingly, Bragg reflection also occurs for light in a wave number space region having a finite thickness shown in FIG. 21 near the combination of the incident angle and wavelength that satisfies the Bragg condition (this is called "light in the optical band gap"). On the other hand, according to the principle of wave number uncertainty, even if the cholesteric liquid crystal polymer layer material has a narrow optical band gap width, the wave number uncertainty can be increased and the region where Bragg reflection occurs can be expanded by reducing the film thickness of the cholesteric liquid crystal polymer layer. However, in this case, the reflectance of the Bragg reflection decreases and the light transmitted through the cholesteric liquid crystal polymer layer increases. This method cannot be used for the notch filter 13, but it can be used for a holographic combiner, etc., and is effective when you want to increase the transmittance.

[0136] In other words, incident light in the wave number space within a range where the Bragg condition is relaxed by the optical band gap width causes Bragg reflection. This is the reason why Bragg reflection occurs within a certain range of incident angles, as shown in Figure 21. The change in wave number vector Dv at this time is different from the Bragg wave number vector for incident light that does not satisfy the Bragg condition, but is aligned with the helical axis direction AX when the helical 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 helical axis direction AX is inclined to the film surface of the cholesteric liquid crystal polymer layer.

[0137] 22, the magnitude of the in-plane component of the Bragg wave vector of the cholesteric liquid crystal polymer layer is expressed as 4π×sinα / P using the magnitude 4π / P of the Bragg wave vector and the tilt angle α of the helical axis. For example, the in-plane component VCr of the Bragg wave vector Vwr is expressed as 4π×sinα / P R The wave vector of the emitted light is determined so that the in-plane component of this Bragg wave vector becomes the in-plane component of the change in the wave vector.

[0138] As mentioned above, the law of conservation of energy and the effective refractive index n effis approximated by the volume average refractive index value of the cholesteric liquid crystal polymer layer, and the effective refractive index n eff can be approximated as being independent of the direction of the wave vector. Therefore, it is possible to impose a condition that the end points of the wave vectors of the incident light and the outgoing light are located on the Ewald sphere, and the wave vector of the outgoing light is uniquely determined with respect to the incident light from this condition and the condition of the in-plane direction component of the change in the wave vector.

[0139] This relationship between the wave vector of the incident light and the wave vector of the outgoing light is actually the same as that of a surface relief type diffraction grating, where the magnitude of the wave vector is 4π×sinα / P. The differences between this relationship and a surface relief type diffraction grating are that only light within the optical band gap is diffracted, excess higher-order diffraction is unlikely to occur, and diffraction occurs only for circularly polarized light of one polarity.

[0140] A cholesteric liquid crystal made for light with a long wavelength will only cause Bragg reflection for light with a shorter wavelength in a range of incident angles larger than that for light with a longer wavelength. For example, in the incident angle range Rrg, the cholesteric liquid crystal polymer layer for red light will Bragg reflect green light. In the incident angle range Rrb, the cholesteric liquid crystal polymer layer for red light will Bragg reflect blue light. In the incident angle range Rgb, the cholesteric liquid crystal polymer layer for green light will Bragg reflect blue light. However, it can be seen that there is no problem if the incident angle range in which the shorter wavelength light causes Bragg reflection is designed not to overlap with the incident angle range Rf. The incident angle range Rf is the range of incident angles in which the filter functions as a notch filter for all wavelengths of red, green, and blue light.

[0141] Here, the estimated incidence angle range Rf is the incidence angle within a cholesteric liquid crystal polymer layer having an effective refractive index of 1 or more, and is not the incidence angle from the atmosphere. When light enters a cholesteric liquid crystal polymer layer from the atmosphere, it is refracted according to the effective refractive index. Therefore, it can be seen that the incidence angle range from the atmosphere can be made larger by using a cholesteric liquid crystal polymer with a large effective refractive index.

[0142] In order to widen the incidence 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 is as parallel as possible to the direction of the incident wave vector when the central ray of the beam at the center of the field of view reaches the center of the eyebox and enters the notch filter 13. Furthermore, after satisfying this condition, the installation angle and the helical axis direction AX of the notch filter 13 may be set so that the helical axis is perpendicular to the film surface.

[0143] Next, the cholesteric liquid crystal polymer layer in the reflector 53 will be described in detail with reference to Fig. 23 and Fig. 24. Fig. 23 is a diagram showing the wave number space of light and the Ewald spheres of blue light and red light in a cross section including the wave number vector in the helical axis direction of the cholesteric liquid crystal polymer and the wave number vector of the center of the beam that is the center of the field of view among the incident light. Here, the helical axis direction AX of the cholesteric liquid crystal polymer layer is inclined at an angle α with respect to the film surface. In Fig. 23 and Fig. 24, for convenience of explanation, the elements corresponding to the cholesteric liquid crystal polymer layer of the notch filter 13 are given the same reference numerals and duplicate explanations are omitted.

[0144] Since the reflector 53 is incident with circularly polarized red and blue light of the same polarity, it is necessary to consider the wave number space for red and blue light, where wavelength selectivity is an issue. As described above, a cholesteric liquid crystal made for light with a long wavelength causes Bragg reflection for light with a shorter wavelength only in a range of incident angles larger than the assumed range of incident angles for the above-mentioned long wavelength light. For example, in the incident angle range Rrb, the cholesteric liquid crystal polymer layer for red light Bragg reflects blue light. However, it can be seen that there is no problem if the incident angle range Rrb is designed so that it does not overlap with the incident angle range Rg1. The incident angle range Rg1 is the range of incident angles that functions as a diffraction grating for the wavelengths of red and blue light.

[0145] Here, the estimated incident angle range Rg1 is the incident angle within a cholesteric liquid crystal polymer layer having an effective refractive index of 1 or more, and is not the incident angle from the atmosphere. When light enters a cholesteric liquid crystal polymer layer from the atmosphere, it is refracted according to the effective refractive index. Therefore, it can be seen that the range of incident angles from the atmosphere can be made larger by using a cholesteric liquid crystal polymer with a large effective refractive index.

[0146] Since the green light is circularly polarized with a different polarity from the red and blue lights, wavelength selectivity is not an issue. Therefore, the green light can be considered independently of the red and blue lights. As shown in FIG. 24, the optical band gap width Wg of the cholesteric liquid crystal polymer layer for the green light may be widened as much as possible.

[0147] In the holographic combiner, in order to realize the function of a concave mirror, it is necessary to change the required tilt α of the helical axis and the in-plane direction of the tilt depending on the location. The tilt α of the helical axis and the in-plane direction of the tilt can be controlled by the alignment pattern of the photoalignment layer. In order to obtain a wider viewing angle, the helical pitch may be changed depending on the location. For example, by utilizing the temperature dependence of the helical pitch of the cholesteric liquid crystal, the helical pitch can be changed depending on the location by applying an in-plane temperature distribution in the pre-solidified state of the cholesteric liquid crystal polymer layer. The helical pitch may be changed depending on the location by changing the chiral dopant concentration depending on the location using an inkjet method when applying the liquid crystal. The change in the helical pitch corresponds to the change in the magnitude of the Bragg wave vector.

[0148] Furthermore, by changing the composition of the liquid crystal monomer for each cholesteric liquid crystal polymer layer and depending on the location using an inkjet method when applying the liquid crystal, the magnitude of birefringence of the liquid crystal monomer (here, the difference between the reciprocal of the ordinary refractive index and the reciprocal of the extraordinary refractive index) can be controlled. This allows the width of the optical band gap to be controlled for each cholesteric liquid crystal polymer layer and depending on the location. Control of the optical band gap may be required in conjunction with control of the helical pitch.

[0149] When the angle of incidence with respect to the helical axis and the tilt α of the helical axis are substantially equal, the light exits the holographic combiner perpendicularly, with an in-plane angle of incidence of approximately 2α.

[0150] It is desirable that the diffraction angles of the three colors of light are uniform and chromatic aberration is eliminated. The inclination α of the helical axis of the cholesteric liquid crystal polymer layer for red light constituting the holographic diffraction layer 56 is 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, the wavelength of red light λ R , the wavelength of green light λ G , and the wavelength λ of blue light B When equation (6) expressed using the formula (6) is satisfied, the diffraction angles of the three colors of light are aligned.

number

[0151] Since we are concerned with the diffraction angle when light enters the atmosphere, the effective refractive index does not enter into equation (6). R and helical pitch P R is directly determined by the exposure pattern of the photo-alignment layer of the cholesteric liquid crystal polymer layer for red light. G and helical pitch P G is directly determined by the exposure pattern of the photo-alignment layer of the cholesteric liquid crystal polymer layer for green light. B and helical pitch P B is directly determined by the exposure pattern of the photo-alignment layer of the blue cholesteric liquid crystal polymer layer. Therefore, the elimination of chromatic aberration can be easily achieved.

[0152] In the retinal projection device 1E, the same effect as that of the retinal projection device 1A can be achieved with respect to the configuration common to the retinal projection device 1A. In order to expand the eyebox, it is necessary to widen the allowable range of the incident angle of the beam incident on the optical device 5A. If a broadband element with a large allowable range of the incident angle is used, the allowable range of the wavelength is widened. Since the red wavelength and the green wavelength are close to each other, and the green wavelength and the blue wavelength are close to each other, if the allowable range of the wavelength is widened, stray light due to chromatic aberration may occur. In contrast, in the retinal projection device 1E, the notch filter 13 extracts the left circularly polarized light of the red light Lr, extracts the right circularly polarized light of the green light Lg, and extracts the left circularly polarized light of the blue light Lb.

[0153] Since the holographic diffraction layer 54 reflects (scatters) left circularly polarized light, even if the wavelength tolerance range of the holographic diffraction layer 54 is expanded, the right circularly polarized light of the green light Lg is not easily reflected. Similarly, since the holographic diffraction layer 55 reflects right circularly polarized light, even if the wavelength tolerance range of the holographic diffraction layer 55 is expanded, the left circularly polarized light of the red light Lr and the left circularly polarized light of the blue light Lb are not easily reflected. Similarly, since the holographic diffraction layer 56 reflects left circularly polarized light, even if the wavelength tolerance range of the holographic diffraction layer 56 is expanded, the right circularly polarized light of the green light Lg is not easily scattered. Since the red wavelength and the blue wavelength are separated, the holographic 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 holographic diffraction layer 54, and the left circularly polarized light of the blue light Lb is not easily reflected by the holographic diffraction layer 56. Therefore, the possibility of stray light due to chromatic aberration can be reduced.

[0154] When the twist direction of the twist structure of the electric field vector with the light traveling direction as the axis at a certain time, which is generated by the rotation of the electric field vector of the circularly polarized light, coincides with the twist direction of the twist structure of the liquid crystal molecules of the cholesteric liquid crystal polymer layer, and the incident light satisfies a certain condition, Bragg reflection occurs and the incident light is diffracted and reflected. On the other hand, if the above twist directions are opposite to each other, the incident light is transmitted without Bragg reflection. As described above, by adjusting the helical pitch (more precisely, the product of the helical pitch and the effective refractive index of the cholesteric liquid crystal polymer layer) of the helical structure formed by the liquid crystal molecules of the cholesteric liquid crystal polymer layer, the helical axis direction, the effective refractive index, the twist direction, and the extraordinary and ordinary refractive indices of each layer obtained by slicing the cholesteric liquid crystal polymer layer on a plane perpendicular to the helical axis, circularly polarized light of a desired wavelength and a desired polarization state is reflected.

[0155] In the retinal projection device 1E, the filter layer 32 is configured to reflect right-handed circularly polarized light from the blue light Lb, the filter layer 33 is configured to reflect left-handed circularly polarized light from the green light Lg, and the filter layer 34 is configured to reflect right-handed circularly polarized light from the red light Lr. Therefore, it is possible to extract the left-handed circularly polarized light of the red light Lr, the right-handed circularly polarized light of the green light Lg, and the left-handed circularly polarized light of the blue light Lb, thereby realizing the function of the notch filter 13.

[0156] The holographic diffraction layer 54 is configured to reflect the left circularly polarized light of the blue light Lb, the holographic diffraction layer 55 is configured to reflect the right circularly polarized light of the green light Lg, and the holographic diffraction layer 56 is configured to reflect the left circularly polarized light of the red light Lr. Thus, the function of the reflector 53 can be realized.

[0157] The notch filter 13 may be configured to pass right-handed circularly polarized light of the red light Lr and reflect left-handed circularly polarized light, pass left-handed circularly polarized light of the green light Lg and reflect right-handed circularly polarized light, and pass right-handed circularly polarized light of the blue light Lb and reflect left-handed circularly polarized light. In this case, the optical device 5A is configured to scatter (reflect) right-handed circularly polarized light in a wavelength range including red wavelengths, scatter (reflect) left-handed circularly polarized light in a wavelength range including green wavelengths, and scatter (reflect) right-handed circularly polarized light in a wavelength range including blue wavelengths.

[0158] Next, the manufacturing method of the cholesteric liquid crystal polymer layer (PVG) and PBOE will be described. An example of an azo dye used in the alignment layer is Brilliant Yellow (CAS RN: 3051-11-4, product code: B0783 Brilliant Yellow: Brilliant Yellow 3051-11-4, Tokyo Chemical Industry Co., Ltd.). A solution obtained by dissolving Brilliant Yellow (BY) in dimethylformamide (DMF) is uniformly applied on a transparent substrate 31 by spin coating and dried on a hot plate. The thin film thus obtained is exposed to an interference electric field between desired circularly polarized light, so that the brilliant yellow molecules are aligned. This forms an alignment layer.

[0159] In the case of producing PVG, a solution obtained by dissolving a reactive mesogen containing a chiral dopant and a photopolymerization initiator in a solvent such as toluene is applied onto the alignment layer, and then the solvent is evaporated to form a thin film. In the case of producing PBOE, the process is the same as above, but no chiral dopant is added. After that, when the liquid crystal alignment is stabilized, the thin film is cured using UV light. If the thickness of the thin film obtained by one application of the solution is insufficient, the above application and curing are repeated until the appropriate thickness is obtained. In the case of PBOE, the thickness is controlled to function as a half-wave plate.

[0160] For example, an exposure apparatus described in Non-Patent Document 1 is used for exposing the alignment layer. An example of a right-handed chiral dopant is R5011 (CAS NO. 944537-61-5 Chiral Dopant R5011, Daken Chemical Limited). An example of a left-handed chiral dopant is S5011 (CAS NO. 693227-30-4 Chiral Dopant S5011|Daken Chemical Limited). An example of a reactive mesogen is reactive mesogen RM257 (CAS RN: 174063-87-7, product code: B5356, Tokyo Chemical Industry Co., Ltd.). By doping with a chiral dopant, a helical structure perpendicular to the surface can be easily realized. The periodicity can be controlled by adjusting the twisting power and concentration of the helical dopant.

[0161] The following method can be used to laminate multiple PVGs. After one PVG is formed on the transparent substrate 31, an intermediate layer that does not affect the alignment of the liquid crystal layer is applied onto the liquid crystal layer of the PVG. Then, the next PVG is formed on the intermediate layer. As another method for laminating multiple PVGs, after a PVG is formed on a different substrate, the PVGs may be laminated by repeatedly transferring the PVGs to the same transparent substrate 31 by adhesion and peeling.

[0162] It should be noted that the retinal projection device according to the present disclosure is not limited to the above embodiment.

[0163] The PBOE 44 may be constructed using a metasurface.

[0164] The deflection element 41 may be any element capable of changing the traveling direction of the beam. The deflection element 41 may be, for example, a reflector (mirror). The deflection element 41 may change the traveling direction of the beam by controlling the wavefront using a spatial light modulator (SLM). Specifically, the deflection element 41 may be a variable diffraction grating formed by a liquid crystal SLM.

[0165] (Additional Note) [Clause 1] a projector module including a laser module for emitting laser light, a collimation lens for converting the laser light into a parallel beam, and a movable mirror for scanning with the beam; a projection lens that focuses the beam emitted from the projector module at a focusing position; an optical unit including a deflection element arranged to overlap the focusing position and changing a traveling direction of the beam; an optical device that converts the beam into parallel light and irradiates the light onto a user's retina; a controller that adjusts a direction of the beam by the deflection element in accordance with a position of the pupil of the user; A retinal projection device comprising:

[0166] [Clause 2] A first wave plate is provided between the laser module and the deflection element, and converts linearly polarized light into circularly polarized light. The deflection element is one or more second wave plates that can be switched between a state in which the polarization state of the circularly polarized light is preserved and a state in which the circularly polarized light is converted into circularly polarized light of an opposite polarity, depending on an applied voltage; and one or more Pancharatnam-Berry phase shift elements that convert circularly polarized light into circularly polarized light of an opposite polarity and diffract the circularly polarized light in a diffraction direction according to the polarity of the incident circularly polarized light, A retinal projection device as described in clause 1, wherein the one or more second wave plates and the one or more Pancharatnam-Berry phase optical elements are arranged alternately one by one to form an array.

[0167] [Clause 3] The deflection element further comprises a reflector that reflects the circularly polarized light while preserving the polarity of the circularly polarized light, 3. A retinal projection device as described in clause 2, wherein the reflector is provided at one end of the array.

[0168] [Article 4] The retinal projection device of claim 2 or 3, wherein the one or more Pancharatnam-Berry phase optical elements are constituted by a liquid crystal polymer or a metasurface.

[0169] [Article 5] The retinal projection device according to any one of clauses 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.

[0170] [Article 6] The retinal projection device according to any one of clauses 1 to 5, further comprising a wavefront correction unit that corrects aberration in the wavefront of a light ray that passes through the pupil among the light rays that constitute the beam.

[0171] [Article 7] The retinal projection device described in clause 6, wherein the wavefront correction unit is composed of any one of an LCOS, a liquid crystal lens, and a deformable mirror.

[0172] [Article 8] The retinal projection device according to any one of clauses 1 to 7, further comprising a focusing section provided between the optical unit and the optical device, for focusing the beam.

[0173] [Article 9] The retinal projection device described in any one of clauses 1 to 8, wherein the laser module emits the 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.

[0174] [Article 10] a filter that passes circularly polarized light of a first polarity among the light of the red wavelength and reflects circularly polarized light of a second polarity different from the first polarity, passes circularly polarized light of the green wavelength and reflects circularly polarized light of the first polarity, and passes circularly polarized light of the blue wavelength and reflects circularly polarized light of the second polarity, The optical device is a holographic combiner, The optical device comprises: a first holographic diffractive layer that diffracts circularly polarized light of the first polarity in a first wavelength range that includes the red wavelengths; a second holographic diffractive layer that diffracts circularly polarized light of the second polarity in a second wavelength range that includes the green wavelengths; a third holographic diffractive layer that diffracts circularly polarized light of the first polarity in a third wavelength range that includes the blue wavelengths; 10. A retinal projection device as claimed in claim 9, comprising:

[0175] [Article 11] the first holographic diffraction layer is a helical structure having a helical pitch corresponding to the red wavelength, and is composed of a cholesteric liquid crystal polymer layer having a helical structure with a twist direction that reflects circularly polarized light of the first polarity; the second holographic diffraction layer is a helical structure having a helical pitch corresponding to the green wavelength, and is composed of a cholesteric liquid crystal polymer layer having a helical structure with a twist direction that reflects the circularly polarized light of the second polarity; The retinal projection device described in clause 10, wherein the third holographic diffraction layer is composed of a cholesteric liquid crystal polymer layer having a helical structure with a helical pitch corresponding to the blue wavelength and a helical structure with a twist direction that reflects circularly polarized light of the first polarity.

[0176] [Article 12] The filter comprises: a first filter layer made of a first cholesteric liquid crystal polymer layer having a helical structure with a helical pitch corresponding to the red wavelength and a helical structure with a twist direction that reflects the second polarity of circularly polarized light; a second filter layer made of a second cholesteric liquid crystal polymer layer having a helical structure with a helical pitch corresponding to the green wavelength and a helical structure with a twist direction that reflects the circularly polarized light of the first polarity; a third filter layer made of a third cholesteric liquid crystal polymer layer having a helical structure with a helical pitch corresponding to the blue wavelength and a helical structure with a twist direction that reflects the second polarity of circularly polarized light; 12. A retinal projection device according to claim 10 or 11, comprising: [Explanation of symbols]

[0177] Reference Signs List 1, 1A, 1B, 1C, 1D, 1E...retinal projection device, 2...projector module, 3...projection lens, 4, 4A...optical unit, 5, 5A...optical device, 6...relay lens (focusing section), 7...wavefront correction lens (wavefront correction section), 9...waveplate (first waveplate), 10...controller, 13...notch filter (filter), 21...laser module, 22...collimation lens, 23...movable mirror, 24...wavefront correction lens (wavefront correction section), 25...wavefront correction element (wavefront correction section), 26...waveplate (first waveplate), 32...filter layer (third filter layer), 33...filter layer (second filter layer), 34...filter layer (first filter layer) filter layer), 41, 41A...deflection element, 42...array, 42a...first end, 42b...second end (one end), 43...wave plate (second wave plate), 44...PBOE (Pancharatnam-Berry phase optical element), 45...deflection element, 47...reflector, 54...holographic diffraction layer (third holographic diffraction layer), 55...holographic diffraction layer (second holographic diffraction layer), 56...holographic diffraction layer (first holographic diffraction layer), 433, 434...transparent electrodes (pair of transparent electrodes), 437...liquid crystal layer, 443...liquid crystal layer (liquid crystal polymer), P...focusing position, Px...focusing position, Py...focusing position, PP...pupil.

Claims

1. a projector module including a laser module for emitting laser light, a collimation lens for converting the laser light into a parallel beam, and a movable mirror for scanning with the beam; a projection lens that focuses the beam emitted from the projector module at a focusing position; an optical unit including a deflection element arranged to overlap the focusing position and changing a traveling direction of the beam; an optical device that converts the beam into parallel light and irradiates the light onto a user's retina; a controller that adjusts a direction of the beam by the deflection element in accordance with a position of the pupil of the user; A retinal projection device comprising:

2. A first wave plate is provided between the laser module and the deflection element, and converts linearly polarized light into circularly polarized light. The deflection element is one or more second wave plates that can be switched between a state in which the polarization state of the circularly polarized light is preserved and a state in which the circularly polarized light is converted into circularly polarized light of an opposite polarity, depending on an applied voltage; and one or more Pancharatnam-Berry phase shift elements that convert circularly polarized light into circularly polarized light of an opposite polarity and diffract the circularly polarized light in a diffraction direction according to the polarity of the incident circularly polarized light, The retinal projection device according to claim 1 , wherein the one or more second wave plates and the one or more Pancharatnam-Berry phase optical elements are arranged alternately one by one to form an array.

3. The deflection element further comprises a reflector that reflects the circularly polarized light while preserving the polarity of the circularly polarized light, 3. A retinal projection device as claimed in claim 2, wherein the reflector is provided at one end of the array.

4. The retinal projection device according to claim 2 or 3, wherein the one or more Pancharatnam-Berry phase optical elements are constituted by a liquid crystal polymer or a metasurface.

5. 4. The retinal projection device according to claim 2, wherein the second wave plate comprises a pair of transparent electrodes and a liquid crystal layer provided between the pair of transparent electrodes.

6. 3. The retinal projection device according to claim 1, further comprising a wavefront correction unit that corrects aberration of a wavefront of a light ray that passes through the pupil among the light rays that constitute the beam.

7. The retinal projection device according to claim 6 , wherein the wavefront correction unit is configured by any one of an LCOS, a liquid crystal lens, and a deformable mirror.

8. The retinal projection device according to claim 1 or 2, further comprising a focusing section provided between the optical unit and the optical device, for focusing the beam.

9. 3. The retinal projection device according to claim 1, wherein the laser module emits the 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.

10. a filter that passes circularly polarized light of a first polarity among the light of the red wavelength and reflects circularly polarized light of a second polarity different from the first polarity, passes circularly polarized light of the green wavelength and reflects circularly polarized light of the first polarity, and passes circularly polarized light of the blue wavelength and reflects circularly polarized light of the second polarity, The optical device is a holographic combiner, The optical device comprises: a first holographic diffractive layer that diffracts circularly polarized light of the first polarity in a first wavelength range that includes the red wavelengths; a second holographic diffractive layer that diffracts circularly polarized light of the second polarity in a second wavelength range that includes the green wavelengths; a third holographic diffractive layer that diffracts circularly polarized light of the first polarity in a third wavelength range that includes the blue wavelengths; 10. The retinal projection device of claim 9, comprising:

11. the first holographic diffraction layer is a helical structure having a helical pitch corresponding to the red wavelength, and is composed of a cholesteric liquid crystal polymer layer having a helical structure with a twist direction that reflects circularly polarized light of the first polarity; the second holographic diffraction layer is a helical structure having a helical pitch corresponding to the green wavelength, and is composed of a cholesteric liquid crystal polymer layer having a helical structure with a twist direction that reflects the circularly polarized light of the second polarity; 11. The retinal projection device of claim 10, wherein the third holographic diffractive layer is composed of a cholesteric liquid crystal polymer layer having a helical structure with a helical pitch corresponding to the blue wavelength and a helical structure with a twist direction that reflects circularly polarized light of the first polarity.

12. The filter comprises: a first filter layer including a first cholesteric liquid crystal polymer layer having a helical structure with a helical pitch corresponding to the red wavelength and a helical structure with a twist direction that reflects the second polarity of circularly polarized light; a second filter layer made of a second cholesteric liquid crystal polymer layer having a helical structure with a helical pitch corresponding to the green wavelength and a helical structure with a twist direction that reflects the circularly polarized light of the first polarity; a third filter layer made of a third cholesteric liquid crystal polymer layer having a helical structure with a helical pitch corresponding to the blue wavelength and a helical structure with a twist direction that reflects the second polarity of circularly polarized light; 11. The retinal projection device of claim 10, comprising:

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