Retinal projection device

Abstract

To reduce stray light due to chromatic aberration.SOLUTION: A retinal projection device 1 comprises: an optical unit 4 capable of changing the optical path of a beam; a combiner 5 for converging the beam into parallel rays of light and irradiating a retina of a user with these parallel rays of light; a notch filter 83 for passing left-handed circularly-polarized light through and reflecting right-handed circularly-polarized light out of red wavelength light, passing right-handed circularly-polarized light through and reflecting left-handed circularly-polarized light out of green wavelength light, and passing left-handed circularly-polarized light through out of blue wavelength light; and a controller 10 for controlling the optical unit 4 in accordance with a position of pupil PP of the user. The combiner 5 includes a holographic diffraction layer 56 for scattering the left-handed circularly-polarized light in a first wavelength range including a red wavelength, a holographic diffraction layer 55 for scattering the right-handed circularly-polarized light in a second wavelength range including a green wavelength, and a holographic diffraction layer 54 for scattering the left-handed circularly-polarized light in a third wavelength range including a blue wavelength.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. For example, when a holographic combiner is used as the combiner, in order to expand the eyebox, it is necessary to widen the allowable range of the incidence angle of the beam incident on the holographic combiner. If a broadband element with a large allowable range of incidence angle is used, the allowable range of wavelengths is widened, and there is a risk of stray light due to chromatic aberration.

[0006] The present disclosure describes a retinal projection device that can reduce stray light due to chromatic aberration. [Means for solving the problem]

[0007] A retinal projection device according to one aspect of the present disclosure includes a laser module that emits laser light including a red component having a red wavelength, a green component having a green wavelength, and a blue component having a blue wavelength, a collimation lens that converts the laser light into a parallel beam, and a projector module including a movable mirror for scanning with the beam, a switching unit capable of switching the optical path of the beam, a combiner that converts the beam into parallel light and irradiates the beam onto a user's retina, a notch filter provided between the projector module and the combiner that passes circularly polarized light of a first polarity among red wavelength light and reflects circularly polarized light of a second polarity different from the first polarity, passes circularly polarized light of the second polarity among green wavelength light and reflects circularly polarized light of the first polarity, and passes circularly polarized light of the first polarity among blue wavelength light and reflects circularly polarized light of the second polarity, and a controller that controls the switching unit so that the beam passes through the user's pupil in accordance with the position of the pupil. The combiner includes a first holographic diffractive layer that scatters circularly polarized light of a first polarity in a first wavelength range that includes red wavelengths, a second holographic diffractive layer that scatters circularly polarized light of a second polarity in a second wavelength range that includes green wavelengths, and a third holographic diffractive layer that scatters circularly polarized light of the first polarity in a third wavelength range that includes blue wavelengths.

[0008] In this retinal projection device, a notch filter provided between the projector module and the combiner extracts circularly polarized light of a first polarity from light of a red wavelength, circularly polarized light of a second polarity from light of a green wavelength, and circularly polarized light of a first polarity from light of a blue wavelength, and the circularly polarized light of a first polarity having a red wavelength, the circularly polarized light of a second polarity having a green wavelength, and the circularly polarized light of a first polarity having a blue wavelength are incident on the combiner. Since the first holographic diffraction layer scatters the circularly polarized light of the first polarity, even if the wavelength tolerance range of the first holographic diffraction layer is expanded, the circularly polarized light of the second polarity having a green wavelength close to the red wavelength is not easily scattered. Similarly, since the second holographic diffraction layer scatters the circularly polarized light of the second polarity, the circularly polarized light of the first polarity having a red wavelength close to the green wavelength and the circularly polarized light of the first polarity having a blue wavelength close to the green wavelength are not easily scattered, even if the wavelength tolerance range of the second holographic diffraction layer is expanded. Similarly, since the third holographic diffractive layer scatters circularly polarized light of the first polarity, circularly polarized light of the second polarity having a green wavelength close to the blue wavelength is less likely to be scattered even if the wavelength tolerance range of the third holographic diffractive layer is expanded, which makes it possible to reduce stray light due to chromatic aberration.

[0009] 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 helical structure twisted in 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 helical structure twisted in 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 helical structure twisted in a twist direction that reflects circularly polarized light of a first polarity.

[0010] 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 function of the combiner can be realized.

[0011] In some embodiments, the notch filter may include a first filter constructed from a first cholesteric liquid crystal polymer layer having a helical structure with a helical pitch corresponding to a red wavelength and a helical structure twisted in a twist direction that reflects circularly polarized light of a second polarity, a second filter constructed from a second cholesteric liquid crystal polymer layer having a helical structure with a helical pitch corresponding to a green wavelength and a helical structure twisted in a twist direction that reflects circularly polarized light of the first polarity, and a third filter constructed from a third cholesteric liquid crystal polymer layer having a helical structure with a helical pitch corresponding to a blue wavelength and a helical structure twisted in a twist direction that reflects circularly polarized light of the second polarity.

[0012] 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 is configured to reflect circularly polarized light of the second polarity from light of a red wavelength, the second filter is configured to reflect circularly polarized light of the first polarity from light of a green wavelength, and the third filter 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 notch filter can be realized.

[0013] In some embodiments, the retinal projection device may further include a neutral density filter that attenuates the light reflected by the notch filter. In this case, the light reflected by the notch filter is attenuated by the neutral density filter, so that stray light can be further reduced.

[0014] In some embodiments, the retinal projection device may further include a projection lens that focuses the beam emitted from the projector module at a focusing position. The switching unit may be arranged to overlap the focusing position and may include a deflection element that changes the traveling direction of the beam. In this case, since the deflection element that changes the traveling direction of the beam is arranged near the focusing position, spherical aberration caused by changing the traveling 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.

[0015] 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 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 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 according to 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.

[0016] 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 after the second wave plate is determined according to the polarity of the circularly polarized light. Therefore, the traveling direction of the beam can be changed by the voltage applied to the second wave plate.

[0017] 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.

[0018] 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.

[0019] In some embodiments, the retinal projection device may further include a focusing unit disposed between the switching unit and the combiner to focus the beam. In this case, the switching unit can be disposed at a position away from the combiner. This improves the degree of freedom in arranging the switching unit.

[0020] 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.

[0021] 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. Effect of the Invention

[0022] According to each aspect and embodiment of the present disclosure, it is possible to reduce stray light due to chromatic aberration. [Brief description of the drawings]

[0023] [Figure 1]FIG. 1 is a diagram illustrating a schematic 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 illustrating a schematic configuration of the notch filter illustrated in FIG. [Figure 11] FIG. 11 is a diagram for explaining the principle of the notch filter shown in FIG. [Figure 12] FIG. 12 is a diagram for explaining the principle of the notch filter shown in FIG. [Figure 13] FIG. 13 is a diagram for explaining the principle of the reflector shown in FIG. [Figure 14] FIG. 14 is a diagram for explaining the principle of the reflector shown in FIG. [Figure 15] FIG. 15 is a diagram showing a schematic configuration of a retinal projection device according to another embodiment. [Figure 16] FIG. 16 is a diagram showing a schematic configuration of a retinal projection device according to yet another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] 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.

[0025] A retinal projection device according to an embodiment will be described with reference to FIG. 1. FIG. 1 is a diagram that shows a schematic 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 the near-eye wearable device 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 (switching unit), a combiner 5, a relay lens 6 (focusing unit), a wavefront correction lens 7 (wavefront correction unit), an extraction unit 8, a waveplate 9 (first waveplate), and a controller 10.

[0026] 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 wavefront correction lens 24 (wavefront correction unit).

[0027] The laser module 21 emits laser light of a color and intensity corresponding to the pixels of the image projected on 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. In other words, the laser module 21 emits laser light including a red component having a red wavelength, a green component having a green wavelength, and a blue component having a blue wavelength.

[0028] 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.

[0029] The wavefront correction lens 24 is a lens that corrects 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 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 formed of a liquid crystal lens.

[0030] In the wavefront compensation lens 24, an area through which a light ray passes that corresponds to the center of the visual field when the pupil PP is located at one position and an area through which a light ray passes that corresponds to the center of the visual field when the pupil PP is located at another position are close to each other. Therefore, the wavefront compensation lens 24 adaptively compensates for the wavefront aberration according to the position of the pupil PP. Specifically, the controller 10 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.

[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 wave plate 9 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 9 is disposed between the laser module 21 and the optical unit 4. The wave plate 9 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 9 is disposed after the element that is assumed to operate with linearly polarized light. As the wave plate 9, a true ¼ wave plate is used in consideration of wavelength dispersion, but a ¼+N (N is a natural number) wave plate may also be used.

[0034] The optical unit 4 is a unit capable of switching the optical path of the beam. In this embodiment, 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. Details of the deflection element 41 will be described later.

[0035] 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 beam near the focal point of the beam. The field lens 46 is provided so as to cover a second end 42b (output end) of the array 42, which will be described later.

[0036] The combiner 5 is an optical element that converts the beam into parallel light and irradiates the light on the user's retina. The combiner 5 is a holographic combiner. In this embodiment, the combiner 5 has a function of scattering left-handed circularly polarized light (circularly polarized light of a first polarity) in a wavelength range (first wavelength range) including red wavelengths, scattering right-handed circularly polarized light (circularly polarized light of a second polarity) 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 combiner 5 includes a transparent substrate 51 and a reflector 53.

[0037] The transparent substrate 51 is a substrate having a visible light transmittance that transmits visible light. Examples of the material of the transparent substrate 51 include SiO 2 , optical glass, and optical plastic. The transparent substrate 51 has a surface 51a facing the eyeball E of a user wearing the near-eye wearable device. The transparent substrate 51 may be a lens of the near-eye wearable device (smart glasses).

[0038] 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).

[0039] 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 the blue wavelength and has a helical structure twisted in a twisting direction that reflects left-handed circularly polarized light.

[0040] The holographic diffraction layer 55 is a reflective diffraction grating layer that scatters (reflects) right-handed circularly polarized light in a wavelength range that includes the green wavelength. 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 that has a helical pitch corresponding to the green wavelength and has a helical structure twisted in a twisting direction that reflects right-handed circularly polarized light.

[0041] 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 has a helical structure twisted in a twisting direction that reflects left-handed circularly polarized light.

[0042] 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.

[0043] 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 combiner 5. The relay lens 6 is composed of a convex lens or a lens group that functions as a convex lens.

[0044] 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, for example, of a liquid crystal lens.

[0045] The extraction unit 8 is a unit that extracts desired 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”). The extraction unit 8 includes a neutral density filter 81, a wave plate 82, and a notch filter 83.

[0046] The neutral density filter 81 is a filter for attenuating the light reflected by the notch filter 83. Stray light can be reduced by the neutral density filter 81. The wave plate 82 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 82 is, for example, a quarter wave plate. An absorptive linear polarizer may be used instead of the wave plate 82.

[0047] The notch filter 83 is a circular polarization dependent notch filter, and is a filter for removing unnecessary circularly polarized components from each of the red light Lr, the green light Lg, and the blue light Lb, and extracting desired circularly polarized components. The notch filter 83 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. Details of the notch filter 83 will be described later.

[0048] 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. The controller 10 adjusts the traveling direction of the beam, for example, 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] Each of the transparent substrates 431 and 432 is a substrate having visible light transmissivity that transmits visible light. The transparent substrates 431 and 432 are made of a material having a small birefringence. Examples of materials for the transparent substrates 431 and 432 include SiO 2 , optical glass, and glass substrates 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.

[0053] 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 (Indium Tin Oxide). 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.

[0054] The alignment layer 435 and the alignment layer 436 are layers for controlling the alignment state (orientation) of the liquid crystal molecules Lm1 contained in the liquid crystal layer 437. The constituent material of the alignment layer 435 and the alignment layer 436 is obtained, for example, by rubbing a polyimide layer in one direction. The constituent material may be obtained by applying a material whose molecular orientation changes when irradiated with polarized light, aligning the molecules by irradiating with polarized light, applying a polymerizable liquid crystal layer thereon, aligning the molecules, and polymerizing the liquid crystal molecules to fix their alignment. The constituent material may be obtained by applying a polymerizable material whose molecular orientation changes when irradiated with polarized light, aligning the molecules by irradiating with polarized light, and polymerizing the liquid crystal molecules. The orientation of the material whose molecular orientation changes when irradiated with polarized light gradually deteriorates even at room temperature after alignment, so in many cases it is necessary to fix the orientation in some way. Generally, the alignment layer often has birefringence, and in that case, a layer that appropriately compensates for this is added. 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.

[0055] 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.

[0056] 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.

[0057] 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).

[0058] 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.

[0059] 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).

[0060] The transparent substrate 441 is a substrate having a visible light transmittance that transmits visible light. The transparent substrate 441 is made of a material having a small birefringence as well as a high surface accuracy. Examples of the material of the transparent substrate 441 include SiO 2, optical glass, and glass substrates for liquid crystal displays. Transparent substrate 441 has surface 441a and surface 441b that intersect (here, are perpendicular to) the Z-axis direction.

[0061] The alignment layer 442 is a layer for controlling the arrangement (orientation) 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 material constituting the alignment layer 442 is a material in which the orientation of the molecules changes when irradiated with polarized light. The alignment layer 442 is configured so that the orientation of the liquid crystal molecules Lm2 contained in the liquid crystal layer 443 changes periodically, as described below. The alignment layer 442 can be obtained, for example, by applying a material in which the orientation of the molecules changes in a direction perpendicular to the vibration direction of the electric field caused by the polarized light when irradiated with linearly polarized light, and then exposing the material to an interference electric field of circularly polarized light in which the electric fields rotate in opposite directions on a desired surface.

[0062] 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.

[0063] 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.

[0064] 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. Note that the diffraction directions of left-handed circularly polarized light and right-handed circularly polarized light are opposite to each other. When the deflection element 41 includes a plurality of PBOEs 44, the diffraction angles of the PBOEs 44 may be different from one another.

[0065] 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. In other words, the thickness of the liquid crystal layer 443 is set so that 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, almost no zero-order (straight light) is generated. In the PBOE 44, no second-order or higher-order diffracted light is generated.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] Next, notch filter 83 will be described in detail with reference to Fig. 10 and Fig. 11. Fig. 10 is a diagram that illustrates a schematic configuration of the notch filter illustrated in Fig. 1. Fig. 11 is a partial enlarged view of Fig. 10. As illustrated in Fig. 10, notch filter 83 includes a transparent substrate 31, a filter layer 32 (third filter), a filter layer 33 (second filter), and a filter layer 34 (first filter).

[0079] 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 a small birefringence. If the transparent substrate 31 is made of a material having a large birefringence, the polarization state will be affected by the transparent substrate 31. Examples of materials for the transparent substrate 31 include SiO 2, 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.

[0080] 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 includes a cholesteric liquid crystal polymer layer. This cholesteric liquid crystal polymer layer is a polarization-dependent volume grating (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 twisted in a twisting 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" indicates the direction of twist in the sense of whether it is a right-handed screw or a left-handed screw.

[0081] The filter layer 33 is a layer that reflects left-handed circularly polarized light from the green light Lg to remove left-handed circularly polarized light and extract right-handed circularly polarized light. The filter layer 33 is provided on the filter layer 32. The filter layer 33 includes a cholesteric liquid crystal polymer layer. This cholesteric liquid crystal polymer layer is 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 twisted in a twisting direction that reflects left-handed circularly polarized light.

[0082] 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 includes a cholesteric liquid crystal polymer layer. This cholesteric liquid crystal polymer layer is 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 twisted in a twisting direction that reflects right-handed circularly polarized light.

[0083] Although not shown in FIG. 10, each cholesteric liquid crystal polymer layer is formed on an alignment layer for controlling the alignment state of liquid crystal molecules contained in the cholesteric liquid crystal polymer layer.

[0084] Here, the cholesteric liquid crystal polymer layer in the notch filter 83 will be described in detail with reference to Fig. 11 and Fig. 12. Fig. 11 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.

[0085] 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.

[0086] 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

[0087] Half pitch P / 2, wavelength of incident light λ, effective refractive index n eff Using 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

[0088] 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

[0089] 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

[0090] 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 Boand 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

[0091] 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.

[0092] 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.

[0093] 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. 11 near the combination of the incident angle and wavelength that satisfies the Bragg condition (this is called "light within 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 83, but can be used for a holographic combiner, etc., and is effective when it is desired to increase the transmittance.

[0094] 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 11. 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 it 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.

[0095] 12, 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] In order to widen the incidence angle range Rf of the notch filter 83, 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 83. Furthermore, after satisfying this condition, the installation angle and the helical axis direction AX of the notch filter 83 may be set so that the helical axis is perpendicular to the film surface.

[0101] Next, the cholesteric liquid crystal polymer layer in the reflector 53 will be described in detail with reference to Fig. 13 and Fig. 14. Fig. 13 is a cross-sectional view of the wave number space of light and the Ewald spheres of blue and red light, including the wave number vector in the direction of the helical axis 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. 13 and Fig. 14, for convenience of explanation, the same reference numerals are given to elements corresponding to the cholesteric liquid crystal polymer layer of the notch filter 83, and duplicate explanations are omitted.

[0102] 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.

[0103] 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.

[0104] 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. 14, the optical band gap width Wg of the cholesteric liquid crystal polymer layer for the green light may be widened as much as possible.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] 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

[0109] 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.

[0110] 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 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.

[0111] 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.

[0112] 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.

[0113] The following method can be used to laminate multiple PVGs. After one PVG is formed on a transparent substrate, an intermediate layer that does not affect the alignment of the liquid crystal layer is applied on the liquid crystal layer of the PVG. The next PVG is then formed on the intermediate layer. As another method for laminating multiple PVGs, the PVGs may be formed on another substrate, and then the PVGs may be laminated on the same transparent substrate by repeatedly transferring the PVGs by adhesion and peeling.

[0114] Next, the effects of the retinal projection device 1 will be described. In order to expand the eyebox, it is necessary to widen the allowable range of the incident angle of the beam entering the combiner 5. If a broadband element with a large allowable range of incident angles is used, the allowable range of wavelengths will be widened. However, since the red wavelengths and the green wavelengths are close to each other, and the green wavelengths and the blue wavelengths are close to each other, there is a risk that stray light due to chromatic aberration will occur if the allowable range of wavelengths is widened.

[0115] In contrast, in the retinal projection device 1, the notch filter 83 provided between the projector module 2 and the combiner 5 extracts the left circularly polarized light of the red light Lr, the right circularly polarized light of the green light Lg, and the left circularly polarized light of the blue light Lb, and the left circularly polarized light of the red light Lr, the right circularly polarized light of the green light Lg, and the left circularly polarized light of the blue light Lb are incident on the combiner 5. Since the holographic diffraction layer 54 reflects (scatters) the 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 the 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-handed circularly polarized light, even if the wavelength tolerance range of the holographic diffraction layer 56 is expanded, the right-handed circularly polarized light of the green light Lg is unlikely to be scattered. Since the red wavelength and the blue wavelength are separated, the holographic diffraction layers 54, 56 can maintain wavelength selectivity. Therefore, the left-handed circularly polarized light of the red light Lr is unlikely to be reflected by the holographic diffraction layer 54, and the left-handed circularly polarized light of the blue light Lb is unlikely to be reflected by the holographic diffraction layer 56. As a result, it is possible to reduce stray light due to chromatic aberration.

[0116] 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. In the retinal projection device 1, 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, and the function of the notch filter 83 can be realized.

[0117] 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.

[0118] A neutral density filter 81 is provided between the notch filter 83 and the relay lens 6. According to this configuration, the light reflected by the notch filter 83 is attenuated by the neutral density filter 81, so that stray light can be further reduced.

[0119] When deflection is performed at a position away from the focusing position P, the focusing at the (virtual) focusing point formed 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 rear stage is designed to 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. This is expressed here as "spherical aberration". On the other hand, when deflection is performed at the focusing position P, the focusing at the focusing point is completely maintained, and spherical aberration is reduced. In the retinal projection device 1, the deflection element 41 is arranged near the focusing position P, so that spherical aberration caused by the change in the traveling direction of the beam (deflection) is reduced. Therefore, the quality of the image formation on the retina is maintained, and the user can correctly recognize the image.

[0120] 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.

[0121] In the wave plate 43, a liquid crystal layer 437 is provided between the transparent electrodes 433 and 434. According to this configuration, by applying a voltage between the transparent electrodes 433 and 434, 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 electrodes 433 and 434, 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 electrodes 433 and 434, 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 electrodes 433 and 434, 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.

[0122] The PBOE 44 is made of a liquid crystal polymer, which makes it easy to form the PBOE 44.

[0123] The focal point of the combiner 5 is located in front of the combiner 5. Therefore, if the relay lens 6 is not provided, the optical unit 4 needs to be placed at the focal point of the combiner 5. In this case, there is a risk that the optical unit 4 will block the user's field of vision. In response to this, in the retinal projection device 1, the relay lens 6 is provided between the optical unit 4 and the combiner 5. With this configuration, the optical unit 4 can be provided at a position away from the combiner 5. Therefore, the degree of freedom in the placement of the optical unit 4 can be improved, and the user's field of vision can be ensured.

[0124] 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.

[0125] A variable wavefront correction lens 24 is provided between the collimation lens 22 and the movable mirror 23. This makes it possible to effectively correct third-order or higher aberrations that occur when a beam as shown in FIG. 1 is obliquely incident on an optical element such as the combiner 5. Although the aberration depends on the angle and position of the beam, the wavefront correction function of the wavefront correction lens 24 may be set so as to provide the best correction for a 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. For this purpose, 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 correction lens 24 to maintain high resolution at the center of the visual field of the naked eye.

[0126] 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.

[0127] 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.

[0128] Next, a retinal projection device according to another embodiment will be described with reference to Fig. 15. Fig. 15 is a diagram showing a schematic configuration of a retinal projection device according to another embodiment. The retinal projection device 1A shown in Fig. 15 differs from the retinal projection device 1 mainly in that it does not include a wavefront correction lens 7 and that the projector module 2 includes a wave plate 26 (first wave plate) instead of the wave plate 9.

[0129] The wave plate 26 is an optical element that converts linearly polarized light into circularly polarized light and is provided after the wavefront correction lens 24.

[0130] In the retinal projection device 1A, the configuration common to the retinal projection device 1 achieves the same effects as the retinal projection device 1. In the retinal projection device 1A, the wavefront correction lens 7 is not provided, and the projector module 2 includes a wavefront correction lens 24. The wavefront correction lens 24 adaptively corrects the wavefront aberration according to the position of the pupil PP, thereby 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.

[0131] Next, a retinal projection device according to still another embodiment will be described with reference to Fig. 16. Fig. 16 is a diagram showing a schematic configuration of a retinal projection device according to still another embodiment. The retinal projection device 1B shown in Fig. 16 differs from the retinal projection device 1A mainly in that the projector module 2 includes a reflective wavefront compensation element 25 (wavefront compensation unit) instead of the wavefront compensation lens 24. A waveplate 26 is provided after the wavefront compensation element 25.

[0132] 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.

[0133] In the retinal projection device 1B, the configuration common to the retinal projection device 1A achieves the same effects as the retinal projection device 1A. In the retinal projection device 1B, the projector module 2 includes a wavefront compensation element 25. The wavefront compensation element 25 adaptively compensates for wavefront aberration according to the position of the pupil PP, thereby further improving the resolution at the center of the visual field. The wavefront compensation element 25 is composed of a deformable mirror or LCOS. The wavefront compensation element 25 can be easily realized by using a deformable mirror or LCOS.

[0134] It should be noted that the retinal projection device according to the present disclosure is not limited to the above embodiment.

[0135] The PBOE 44 may be constructed using a metasurface.

[0136] 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.

[0137] The notch filter 83 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 combiner 5 is configured to diffract (Bragg reflection) right-handed circularly polarized light in a wavelength range including red wavelengths, diffract (Bragg reflection) left-handed circularly polarized light in a wavelength range including green wavelengths, and diffract (Bragg reflection) right-handed circularly polarized light in a wavelength range including blue wavelengths.

[0138] (Additional Note) [Clause 1] a laser module that emits laser light including a red component having a red wavelength, a green component having a green wavelength, and a blue component having a blue wavelength, a collimation lens that converts the laser light into a parallel beam, and a projector module that includes a movable mirror for scanning with the beam; A switching unit capable of switching an optical path of the beam; a combiner that converts the beam into parallel light and irradiates the parallel light onto a user's retina; a notch filter provided between the projector module and the combiner, the notch filter passing circularly polarized light of a first polarity among the light of the red wavelength and reflecting circularly polarized light of a second polarity different from the first polarity, passing circularly polarized light of the second polarity among the light of the green wavelength and reflecting circularly polarized light of the first polarity, and passing circularly polarized light of the first polarity among the light of the blue wavelength and reflecting circularly polarized light of the second polarity; a controller that controls the switching unit in accordance with a position of the user's pupil so that the beam passes through the pupil; Equipped with The combiner includes: 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; A retinal projection device comprising:

[0139] [Clause 2] 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 twisted in a twist direction that reflects the 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 twisted in a twist direction that reflects the second polarity of circularly polarized light; The retinal projection device described in clause 1, 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 twisted in a twist direction that reflects circularly polarized light of the first polarity.

[0140] [Clause 3] The notch filter comprises: a first filter including a first cholesteric liquid crystal polymer layer having a helical structure with a helical pitch corresponding to the red wavelength and twisted in a twist direction that reflects the second polarity of circularly polarized light; a second filter including a second cholesteric liquid crystal polymer layer having a helical structure with a helical pitch corresponding to the green wavelength and twisted in a twist direction that reflects the first polarity of circularly polarized light; a third filter including a third cholesteric liquid crystal polymer layer having a helical structure with a helical pitch corresponding to the blue wavelength and twisted in a twisting direction that reflects the second polarity of circularly polarized light; 3. A retinal projection device according to claim 1 or 2, comprising:

[0141] [Article 4] The retinal projection device according to any one of clauses 1 to 3, further comprising a neutral density filter that attenuates light reflected by the notch filter.

[0142] [Article 5] a projection lens for focusing the beam emitted from the projector module at a focusing position; The retinal projection device according to any one of clauses 1 to 4, wherein the switching unit is arranged so as to overlap with the focusing position and includes a deflection element that changes the traveling direction of the beam.

[0143] [Article 6] 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 the opposite polarity, depending on an applied voltage; and one or more Pancharatnam-Berry phase optical 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, 6. A retinal projection device as described in clause 5, wherein the one or more second wave plates and the one or more Pancharatnam-Berry phase optical elements are arranged alternately one by one.

[0144] [Article 7] The retinal projection device of clause 6, wherein the one or more Pancharatnam-Berry phase optical elements are composed of a liquid crystal polymer or a metasurface.

[0145] [Article 8] The retinal projection device described in clause 6 or clause 7, wherein the second wave plate comprises a pair of transparent electrodes and a liquid crystal layer disposed between the pair of transparent electrodes.

[0146] [Article 9] The retinal projection device according to any one of clauses 5 to 8, further comprising a focusing section provided between the switching section and the combiner, for focusing the beam.

[0147] [Article 10] The retinal projection device according to any one of clauses 1 to 9, 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.

[0148] [Article 11] The retinal projection device described in clause 10, wherein the wavefront correction unit is composed of any one of an LCOS, a liquid crystal lens, and a deformable mirror. [Explanation of symbols]

[0149] Reference Signs List 1, 1A, 1B...retinal projection device, 2...projector module, 3...projection lens, 4...optical unit (switching unit), 5...combiner, 6...relay lens (focusing unit), 7...wavefront correction lens (wavefront correction unit), 9...waveplate (first waveplate), 10...controller, 21...laser module, 22...collimation lens, 23...movable mirror, 24...wavefront correction lens (wavefront correction unit), 25...wavefront correction element (wavefront correction unit), 26...waveplate (first waveplate), 32...filter layer (third filter), 33...filter layer (second filter), 34...filter layer (first filter), 41...deflection element, 43...wave plate (second wave plate), 44...PBOE (Pancharatnam-Berry phase optical element), 54...holographic diffraction layer (third holographic diffraction layer), 55...holographic diffraction layer (second holographic diffraction layer), 56...holographic diffraction layer (first holographic diffraction layer), 81...neutral reduction filter, 83...notch filter, 433, 434...transparent electrodes (pair of transparent electrodes), 437...liquid crystal layer, 443...liquid crystal layer (liquid crystal polymer), P...focus position, PP...pupil.

Claims

1. a laser module that emits laser light including a red component having a red wavelength, a green component having a green wavelength, and a blue component having a blue wavelength, a collimation lens that converts the laser light into a parallel beam, and a projector module that includes a movable mirror for scanning with the beam; A switching unit capable of switching an optical path of the beam; a combiner that converts the beam into parallel light and irradiates the parallel light onto a user's retina; a notch filter provided between the projector module and the combiner, the notch filter passing circularly polarized light of a first polarity among the light of the red wavelength and reflecting circularly polarized light of a second polarity different from the first polarity, passing circularly polarized light of the second polarity among the light of the green wavelength and reflecting circularly polarized light of the first polarity, and passing circularly polarized light of the first polarity among the light of the blue wavelength and reflecting circularly polarized light of the second polarity; a controller that controls the switching unit in accordance with a position of the user's pupil so that the beam passes through the pupil; Equipped with The combiner includes: 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; A retinal projection device comprising:

2. 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 twisted in a twist direction that reflects the 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 twisted in a twist direction that reflects the second polarity of circularly polarized light; 2. The retinal projection device of claim 1, 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 twisted in a twist direction that reflects circularly polarized light of the first polarity.

3. The notch filter comprises: a first filter including a first cholesteric liquid crystal polymer layer having a helical structure with a helical pitch corresponding to the red wavelength and twisted in a twist direction that reflects the second polarity of circularly polarized light; a second filter including a second cholesteric liquid crystal polymer layer having a helical structure with a helical pitch corresponding to the green wavelength and twisted in a twist direction that reflects the circularly polarized light of the first polarity; a third filter including a third cholesteric liquid crystal polymer layer having a helical structure with a helical pitch corresponding to the blue wavelength and twisted in a twisting direction that reflects the second polarity of circularly polarized light; 3. A retinal projection device according to claim 1 or claim 2, comprising:

4. 3. A retinal projection device according to claim 1, further comprising a neutral density filter that attenuates light reflected by the notch filter.

5. a projection lens for focusing the beam emitted from the projector module at a focusing position; The retinal projection device according to claim 1 or 2, wherein the switching unit includes a deflection element that is arranged to overlap the focal position and changes the traveling direction of the beam.

6. 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 5 , wherein the one or more second wave plates and the one or more Pancharatnam-Berry phase optical elements are arranged alternately one by one.

7. The retinal projection device of claim 6, wherein the one or more Pancharatnam-Berry phase optical elements are composed of a liquid crystal polymer or a metasurface.

8. 7. The retinal projection device of claim 6, wherein the second wave plate comprises a pair of transparent electrodes and a liquid crystal layer provided between the pair of transparent electrodes.

9. The retinal projection device according to claim 5 , further comprising a focusing section provided between the switching section and the combiner, for focusing the beam.

10. 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.

11. The retinal projection device according to claim 10 , wherein the wavefront correction unit is configured by any one of an LCOS, a liquid crystal lens, and a deformable mirror.

Images