Display device and head-mounted display

Abstract

To provide a display device which is thin and is excellent in the display characteristic and in the productivity, and a head-mount display having the display device.SOLUTION: The display device sequentially includes: a display panel; a half mirror; a lens; a Pancharatnam-Berry lens for collecting one of left circular polarization and right circular polarization which has entered the Pancharatnam-Berry lens and dispersing the other of left circular polarization and right circular polarization which has entered the Pancharatnam-Berry lens; and a circular polarization selective reflection element in descending order of distance to an observer. The side of the lens which is on the circular polarization selective reflection element side is flat.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a display device and a head-mounted display including the display device. [Background technology]

[0002] A head-mounted display (HMD) is a display device that outputs images so that the observer (user) can see the images while wearing it on their head. For example, there is an immersive HMD that covers both eyes and allows the observer to see the display on the HMD within their field of vision. Immersive HMDs block external light, providing a deep sense of immersion, and are also called VR (Virtual Reality) devices.

[0003] In recent years, attention has been focused on the virtual space known as the Metaverse, and the market for VR-HMDs is expected to expand as a tool for accessing this world. However, it has been pointed out that VR-HMDs have large housings, and there is a need to make them more compact in order to popularize them more widely.

[0004] As a means of compactification, folded optical systems that utilize the properties of polarization are being developed (Patent Documents 1 and 2). Patent Documents 1 and 2 disclose an adjustment method for moving a virtual image back and forth in the folded optical system. Specifically, Patent Documents 1 and 2 disclose that varifocal lenses, which are lenses for adjusting lens power, are arranged in various locations in the optical system. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2020 / 226867 [Patent Document 2] International Publication No. 2020 / 112965 Summary of the Invention [Problem to be solved by the invention]

[0006] FIG. 24 shows a cross-sectional view of a display device with a folded optical system that enables a more compact HMD. FIG. 24 is an exploded cross-sectional view that shows a schematic diagram of a display device of a comparative embodiment. As shown in FIG. 24, a display device 100R of the comparative embodiment includes, in this order toward a viewer U, a display panel 10, a circular polarization element 20, a half mirror 30, a lens 40R, and a circularly polarized light selective reflection element 50. The circular polarization element 20 includes a first linear polarizer 21 and a first quarter-wave plate 22. The folded optical system shown in the comparative embodiment is also called a pancake lens optical system.

[0007] When the display panel 10 is a liquid crystal panel, a second linear polarizer may be disposed on the opposite side of the display panel 10 from the circular polarizer 20. In the comparative display device 100R, the functional layers and lenses may be bonded together or may be separated by air. Furthermore, multiple lenses may be used instead of one.

[0008] The half mirror 30 has the function of reflecting 50% of the incident light and transmitting the remaining 50%. Therefore, of the light that is emitted from the display panel 10 and transmitted through the circular polarization element 20, 50% is transmitted through the half mirror 30 and emitted toward the viewer U, and the remaining 50% is reflected by the half mirror 30 and emitted toward the display panel 10. Furthermore, the light that is transmitted through the half mirror 30 and emitted toward the viewer U is reflected by the circularly polarized light selective reflection element 50 and emitted to the lens 40R. Of the light that is transmitted through the lens 40R and reaches the half mirror 30, 50% is reflected by the half mirror 30 and emitted toward the viewer U, and the remaining 50% is transmitted through the half mirror 30 and emitted toward the display panel 10. That is, 50% of the light emitted from the display panel 10 is reflected by the half mirror 30 toward the display panel 10, resulting in a loss of light and not being visible to the observer U, and 25% of the light emitted from the display panel 10 is transmitted by the half mirror 30 toward the display panel 10, resulting in a loss of light and not being visible to the observer U.

[0009] Examples of the circularly polarized light selective reflection element 50 include a configuration including a second quarter-wave plate and a reflective linear polarizer (for example, a reflective polarizer manufactured by 3M (product name APF)), or a configuration including a cholesteric liquid crystal film.

[0010] When the circularly polarized light selective reflection element 50 comprises a second quarter-wave plate and an APF, linearly polarized light 1L is emitted from the circularly polarized light selective reflection element 50, and when the circularly polarized light selective reflection element 50 comprises a cholesteric liquid crystal film, circularly polarized light 2L is emitted from the circularly polarized light selective reflection element 50.

[0011] A display device 100R with a folded optical system according to a comparative example circularly polarizes image light and is minimally configured to include a half mirror 30, a lens 40R, and a circularly polarized light selective reflection element 50 (e.g., a cholesteric liquid crystal film). Currently, the mainstream displays in HMDs are liquid crystal display devices, and thus circularly polarized light is emitted by placing a first quarter-wave plate 22 on a first linear polarizer 21 provided on a liquid crystal panel serving as a display panel 10. Such a display device 100R with a folded optical system can make the display device thinner.

[0012] In the display device 100R with a folded optical system, it is preferable that the surfaces of the lens 40R facing the half mirror 30 and the circularly polarized light selective reflection element 50 have steep spherical surfaces. This configuration makes it possible to increase the lens power of the lens 40R and improve the display characteristics of the display device 100R. Here, in order to attach the circularly polarized light selective reflection element 50 to the steep spherical surface of the lens 40R when the surface of the lens 40R facing the circularly polarized light selective reflection element 50 has a steep spherical surface, it is preferable that the circularly polarized light selective reflection element 50 also has a steep spherical surface. However, because circularly polarized light selective reflection elements are generally supplied as films, it is difficult to manufacture a circularly polarized light selective reflection element having a steep spherical surface. For example, the circularly polarized light selective reflection element 50 has a flat shape or a gently spherical surface (generally with a radius of curvature R of 150 mm or more). Therefore, attaching the circularly polarized light selective reflection element 50 to the lens 40R having a steep spherical surface is more difficult than attaching the circularly polarized light selective reflection element 50 to a flat surface, and there is a high possibility that productivity, such as reliability and yield, will be adversely affected. Therefore, it is difficult to obtain a thin display device 100R that is excellent in both display characteristics and productivity.

[0013] The above Patent Documents 1 and 2 do not consider a display device that is thin and has excellent display characteristics and productivity.

[0014] The present invention has been made in consideration of the above-described current situation, and aims to provide a display device that is thin and has excellent display characteristics and productivity, and a head-mounted display that includes the display device. [Means for solving the problem]

[0015] (1) One embodiment of the present invention is a display device comprising, in order facing the observer, a display panel, a half mirror, a lens, a Pancharatnam Berry lens that focuses incident left-handed or right-handed circularly polarized light and diverges incident right-handed circularly polarized light, and a circularly polarized light selective reflection element, wherein the surface of the lens facing the circularly polarized light selective reflection element is flat.

[0016] (2) Furthermore, in addition to the configuration of (1), another embodiment of the present invention is a display device, wherein the lens includes a first lens portion and a second lens portion.

[0017] (3) Furthermore, in one embodiment of the present invention, in addition to the configuration of (1) or (2), the lens is a first lens, the circularly polarized light selective reflection element is a first circularly polarized light selective reflection element, and further, between the display panel and the half mirror, a second circularly polarized light selective reflection element, a display panel-side Pancharatnamveli lens, and a second lens are provided in this order toward the observer side, and the surface of the second lens facing the second circularly polarized light selective reflection element is flat.

[0018] (4) Furthermore, in one embodiment of the present invention, in addition to the configuration of (1), (2), or (3), the display device further comprises an observer-side Pancharatnam Berry lens between the circularly polarized light selective reflection element and the observer.

[0019] (5) Another embodiment of the present invention is a head-mounted display comprising a display device according to any one of (1), (2), (3), or (4) above, and a mounting unit to be mounted on the head of the observer. [Effects of the Invention]

[0020] According to the present invention, it is possible to provide a display device that is thin and has excellent display characteristics and productivity, and a head-mounted display including the display device. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is an exploded schematic view showing a display device according to Embodiment 1. FIG. [Figure 2] FIG. 2 is a plan view of a PB lens. [Figure 3] 10A and 10B are schematic diagrams illustrating an example of light collection and divergence of a PB lens. [Figure 4] 1 is an example of an exploded cross-sectional view of a display device according to a first embodiment. [Figure 5] 1 is an example of an exploded cross-sectional view of a display device according to a first embodiment. [Figure 6] FIG. 2 is a plan view showing an example of a PB lens. [Figure 7] FIG. 2 is a plan view showing an example of a PB lens. [Figure 8] 3 is a cross-sectional view of an example of a PB lens included in the display device of the first embodiment. [Figure 9] 1 is an exploded schematic view showing a display device according to a first modified example of the first embodiment. FIG. [Figure 10] 10 is an exploded schematic view showing a display device according to Modification 2 of Embodiment 1. FIG. [Figure 11] 3 is an exploded schematic view showing a ghost that may occur in the display device according to the first embodiment. FIG. [Figure 12] FIG. 10 is an exploded schematic view showing a display device according to a second embodiment. [Figure 13] 10 is an exploded schematic view showing a display device according to a first modification of the second embodiment. FIG. [Figure 14] FIG. 10 is an exploded schematic view showing a ghost that may occur in the display device according to the second embodiment. [Figure 15] FIG. 10 is an exploded cross-sectional view schematically showing a display device according to a third embodiment. [Figure 16] FIG. 16 is a schematic plan view of the liquid crystal panel shown in FIG. [Figure 17] FIG. 10 is a perspective view schematically illustrating an example of the appearance of a head-mounted display according to a fourth embodiment. [Figure 18] 1A and 1B are an exploded schematic view and a simulation diagram showing a display device according to Comparative Example 1. FIG. [Figure 19] FIG. 19 is an enlarged view of the area surrounded by the dashed line in FIG. 18. [Figure 20] FIG. 10 is a diagram showing details of a simulation result of the display device according to Comparative Example 1. [Figure 21] 1A and 1B are an exploded schematic view and a simulation diagram showing a display device according to Example 1. FIG. [Figure 22]FIG. 22 is an enlarged view of the area surrounded by the dashed line in FIG. 21. [Figure 23] FIG. 4 is a diagram showing details of a simulation result of the display device according to the first embodiment. [Figure 24] FIG. 10 is an exploded cross-sectional view schematically showing a display device of a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0022] The present invention will be described in more detail below with reference to the drawings and with reference to the following embodiments, but the present invention is not limited to these embodiments.

[0023] <Embodiment 1> Fig. 1 is an exploded schematic diagram showing a display device according to embodiment 1. As shown in Fig. 1, the display device 100 of this embodiment includes, in order toward a viewer U, a display panel 10, a half mirror 30, a lens 40, a Pancharatnam Berry lens 40PB that focuses incident left-handed circularly polarized light and right-handed circularly polarized light and diverges incident right-handed circularly polarized light, and a circularly polarized light selective reflection element 50, and the surface of the lens 40 facing the circularly polarized light selective reflection element 50 is flat.

[0024] This configuration makes it possible to realize a folding optical system using the half mirror 30, thereby enabling the display device 100 to be made thinner. Furthermore, the Pancharatnam Berry lens 40PB can be given the lens power obtained when the surface of the lens 40 facing the circularly polarized light selective reflection element 50 is spherical. This allows the surface of the lens 40 facing the circularly polarized light selective reflection element 50 to be flat, thereby improving the display characteristics of the display device 100. For example, it is possible to shorten the length of the optical system of the display device 100, improve the MTF (Modulation Transfer Function) performance, which is an index of lens performance, and widen the FOV (Field Of View). Furthermore, since the surface of the lens 40 facing the circularly polarized light selective reflection element 50 is flat, the circularly polarized light selective reflection element 50 can be easily bonded to the lens 40, thereby improving productivity.

[0025] In display device 100R of comparative form 1, in order to shorten the length of the optical system, improve the MTF performance (an index of lens performance), and widen the FOV (field of view), it is necessary to make the lens surface of lens 40R on the side of circularly polarized light selective reflection element 50 spherical, as described above. In this case, circularly polarized light selective reflection element 50 must be attached to the spherical surface, which is more difficult than attaching it to a flat surface, and there is a high possibility that productivity, such as reliability and yield, will decrease.

[0026] 1, display device 100 of the present embodiment includes Pancharatnam Berry lens 40PB in addition to the configuration of display device 100R of the comparative example. This configuration allows Pancharatnam Berry lens 40PB to take on part of the lens power of the spherical surface of lens 40. As a result, the surface of lens 40 facing circularly polarized light selective reflection element 50 can be made flat, making it easier to attach circularly polarized light selective reflection element 50 and improving productivity.

[0027] The above Patent Documents 1 and 2 describe an embodiment in which the optical system includes a PB lens, but do not disclose the shape of the lens when both a lens and a PB lens are included.

[0028] Furthermore, the above Patent Documents 1 and 2 are technologies for moving a virtual image, and do not consider improving image quality in an optical system. On the other hand, the display device 100 of this embodiment is capable of improving image quality. Specifically, the display device 100 of this embodiment makes it possible to optimize image quality and achieve a wide FOV. Therefore, the purpose of arranging the PB lens differs between the display device 100 of this embodiment and the display devices of Patent Documents 1 and 2. This embodiment will be described in detail below. Hereinafter, the Pancharatnam Berry lens will also be referred to as the PB lens.

[0029] As shown in Figure 1, the display device 100 of this embodiment includes, in order toward the observer U, a display panel 10, a circular polarization element 20, a half mirror 30, a lens 40, a PB lens 40PB, and a circular polarization selective reflection element 50.

[0030] FIG. 1 illustrates an example in which the circular polarization element 20 includes a laminate of a first linear polarizer 21 and a first quarter-wave plate 22. In the exploded cross-sectional views in this specification, although the components are shown with a gap between them, the components may be bonded together or spaced apart. That is, the functional layers and lenses may be bonded together or may be spaced apart by air. Furthermore, multiple lenses may be used instead of one.

[0031] As shown in FIG. 1, the display panel 10 emits light (display light) toward the viewer U, and the first linear polarizer 21 converts the display light of the display panel 10 into linearly polarized light. The linearly polarized light that passes through the first quarter-wave plate 22 is converted into circularly polarized light ((i) of FIG. 1). If the circularly polarized light is right-handed circularly polarized light, the right-handed circularly polarized light passes through the half mirror 30 ((ii) of FIG. 1) and then passes through the lens 40 without changing its rotation direction ((iii) of FIG. 1). The right-handed circularly polarized light that has passed through the PB lens 40PB is converted into left-handed circularly polarized light, which is the reverse rotation of the light ((iv) of FIG. 1).

[0032] The left-handed circularly polarized light emitted from the PB lens 40PB is selectively reflected by the circularly polarized light selective reflection element 50 (FIG. 1(v)), and the reflected left-handed circularly polarized light passes through the PB lens 40PB again and is converted into right-handed circularly polarized light with the opposite rotation (FIG. 1(vi)). The right-handed circularly polarized light emitted from the PB lens 40PB passes through the lens 40 without changing its direction of rotation (FIG. 1(vii)), and is reflected by the half mirror 30 and converted into left-handed circularly polarized light (FIG. 1(viii)).

[0033] The left-handed circularly polarized light emitted from the half mirror 30 passes through the lens 40 without changing its direction of rotation ((ix) in FIG. 1). The left-handed circularly polarized light emitted from the lens 40 passes through the PB lens 40PB and is converted into right-handed circularly polarized light with the opposite rotation ((x) in FIG. 1). The right-handed circularly polarized light emitted from the PB lens 40PB passes through the circularly polarized light selective reflection element 50 and is emitted toward the observer U ((xi) in FIG. 1).

[0034] The display device 100 of this embodiment is a folding optical system in which light is reflected between the half mirror 30 and the circularly polarized light selective reflection element 50, so that light (display light) emitted from the display panel 10 toward the observer U is folded and emitted toward the observer U, thereby making it possible to make the thickness of the display device 100 thin while lengthening the optical path.

[0035] (display panel) The display panel 10 preferably includes a plurality of pixels. The pixels are display units for displaying images, and in the case of color display, the pixels include, for example, red, blue, and green pixels.

[0036] The display panel 10 may have a TFT substrate on which a plurality of thin film transistors (TFTs) are arranged. The TFT substrate may include a plurality of gate lines extending parallel to one another on a support substrate, and a plurality of source lines extending parallel to one another in a direction intersecting the gate lines with a gate insulating film interposed therebetween. The plurality of gate lines and the plurality of source lines may be formed in a lattice pattern in a plan view, and each region partitioned by the plurality of gate lines and the plurality of source lines corresponds to a pixel.

[0037] The support substrate is preferably a transparent substrate, such as a glass substrate or a plastic substrate.

[0038] A TFT may be disposed at each intersection of each gate line and each source line as a switching element for each pixel. The gate terminal of the TFT may be connected to the gate line, the source terminal may be connected to the source line, and the drain terminal may be connected to the pixel electrode. The display panel 10 may have a common electrode to which a common electrode voltage is applied, in addition to the pixel electrodes.

[0039] The display panel 10 may be an OLED panel including organic light emitting diodes (OLEDs) or a QD-LED panel including quantum dot light emitting diodes (QD-LEDs). In this specification, when there is no need to distinguish between OLEDs and QD-LEDs, they are also referred to as light emitting diodes (LEDs).

[0040] The configuration of the light-emitting diode is not particularly limited, and may be, for example, one in which a cathode, an electron transport layer, a light-emitting layer, a hole transport layer, and an anode are laminated in this order.

[0041] The material for the cathode and anode is not particularly limited, but examples thereof include transparent conductive materials such as ITO (indium tin oxide), IZO (indium zinc oxide), In3O3, SnO2, and ZnO, aluminum, silver, and alloys thereof.

[0042] In the case of a top-emission LED, the pixel electrode of the TFT substrate may be used as the anode, and the common electrode may be used as the cathode. A reflective electrode such as aluminum, silver, or an alloy thereof may be used as the anode, and the transparent conductive material may be used as the cathode.

[0043] The hole transport layer is a layer that transports holes injected from the anode to the light-emitting layer. The material of the hole transport layer is not particularly limited, but examples thereof include amine compounds such as N,N,N',N'-tetraphenylbenzidine and its derivatives.

[0044] The electron transport layer is a layer that transports electrons injected from the cathode to the light-emitting layer. The material of the electron transport layer is not particularly limited, and examples thereof include phenanthroline derivatives such as 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), quinoline derivatives such as tris(8-quinolinolato)aluminum (Alq), azaindolizine derivatives, oxadiazole derivatives, perylene derivatives, pyridine derivatives, pyrimidine derivatives, quinoxaline derivatives, diphenylquinone derivatives, and nitro-substituted fluorene derivatives.

[0045] An electron injection layer may be provided between the cathode and the electron transport layer. Also, a hole injection layer may be provided between the anode and the hole transport layer. As the material for the electron injection layer, an inorganic insulating material can be used, such as an oxide or halide of an alkali metal, or an oxide or halide of an alkaline earth metal.

[0046] When the display panel 10 is an OLED, the light-emitting layer may contain a fluorescent material, a phosphorescent material, or the like as a light-emitting material.

[0047] The red fluorescent material is not particularly limited as long as it emits red fluorescence, and examples thereof include perylene derivatives such as tetraaryldiindenoperylene derivatives, europium complexes, benzopyran derivatives, rhodamine derivatives, benzothioxanthene derivatives, and porphyrin derivatives.

[0048] The green fluorescent material is not particularly limited as long as it emits green fluorescence, and examples thereof include coumarin derivatives, quinacridone derivatives, and anthracene derivatives.

[0049] The blue fluorescent material is not particularly limited as long as it emits blue fluorescence, and examples thereof include distyrylamine derivatives, fluoranthene derivatives, pyrene derivatives, perylene and perylene derivatives, anthracene derivatives, benzoxazole derivatives, benzothiazole derivatives, benzimidazole derivatives, chrysene derivatives, phenanthrene derivatives, distyrylbenzene derivatives, and tetraphenylbutadiene.

[0050] The phosphorescent material is not particularly limited as long as it emits phosphorescence, and examples thereof include metal complexes of iridium, ruthenium, platinum, osmium, rhenium, palladium, etc. The metal complexes preferably have at least one ligand having a phenylpyridine skeleton, a bipyridyl skeleton, a porphyrin skeleton, or the like.

[0051] Red phosphorescent materials include tris(1-phenylisoquinoline)iridium, bis[2-(2'-benzo[4,5-α]thienyl)pyridinate-N,C3']iridium(acetylacetonate) (btp2Ir(acac)), 2,3,7,8,12,13,17,18-octaethyl-12H,23H-porphyrin-platinum(II), bis[2-(2'-benzo[4,5-α]thienyl)pyridinate-N,C3']iridium, and bis(2-phenylpyridine)iridium(acetylacetonate).

[0052] Green phosphorescent materials include fac-tris(2-phenylpyridine)iridium (Ir(ppy)), bis(2-phenylpyridinato-N,C)iridium(acetylacetonate), and fac-tris[5-fluoro-2-(5-trifluoromethyl-2-pyridine)phenyl-C,N]iridium.

[0053] Examples of blue phosphorescent materials include bis[4,6-difluorophenylpyridinate-N,C2′]-picolinate-iridium, tris[2-(2,4-difluorophenyl)pyridinate-N,C2′]iridium, bis[2-(3,5-trifluoromethyl)pyridinate-N,C2′]-picolinate-iridium, and bis(4,6-difluorophenylpyridinate-N,C2′)iridium(acetylacetonate).

[0054] The fluorescent material and phosphorescent material are also called dopants, and the light-emitting layer may contain a host material that transports charges to the dopant. Examples of host materials include acene derivatives (acene compounds) such as anthracene derivatives and tetracene derivatives, distyrylarylene derivatives, perylene derivatives, distyrylbenzene derivatives, distyrylamine derivatives, quinolinolato metal complexes such as tris(8-quinolinolato)aluminum complex (Alq3), triarylamine derivatives such as a tetramer of triphenylamine, oxadiazole derivatives, silole derivatives, dicarbazole derivatives such as 3-phenyl-4-(1'-naphthyl)-5-phenylcarbazole and 4,4'-N,N'-dicarbazolebiphenyl (CBP), oligothiophene derivatives, benzopyran derivatives, triazole derivatives, benzoxazole derivatives, benzothiazole derivatives, quinoline derivatives, and 4,4'-bis(2,2'-diphenylvinyl)biphenyl (DPVBi), which can be used in combination with fluorescent materials or phosphorescent materials as appropriate.

[0055] When the display panel 10 is a QD-LED panel, the light-emitting layer may contain quantum dots as a light-emitting material. Quantum dots are nanoscale (e.g., with an average particle diameter of 2 to 10 nm) semiconductor crystals with optical properties governed by quantum mechanics, such as colloidal particles composed of approximately 10 to 50 atoms.

[0056] The quantum dots include compounds such as cadmium selenium (CdSe), cadmium tellurium (CdTe), cadmium sulfide (CdS), lead sulfide (PbS), or indium phosphide (InP), or alloys such as CdSeS.

[0057] Examples of quantum dots include core-type quantum dots made of semiconductor crystals with a uniform internal composition, alloy-type quantum dots made of an alloy of multiple semiconductors, and core-shell quantum dots in which the surface of core-type quantum dots or alloy-type quantum dots is coated with a semiconductor compound. The emission wavelength peak can be adjusted by adjusting the particle size of the quantum dots. Furthermore, the optical and electronic properties can be adjusted by changing the composition and internal structure of the quantum dots.

[0058] A light-emitting diode (OLED or QD-LED) may be arranged for each pixel. In the case of an OLED panel or a QD-LED panel, a red LED (OLED or QD-LED) having a light-emitting layer containing a red light-emitting material, a green LED having a light-emitting layer containing a green light-emitting material, and a blue LED having a light-emitting layer containing a blue light-emitting material may be arranged in the red, green, and blue pixels, respectively.

[0059] By combining the above fluorescent or phosphorescent materials, it is also possible to produce an OLED that emits white fluorescence or phosphorescence. In the case of an OLED panel, color filters containing red, green, and blue resin layers may be overlaid on a white OLED to form red, green, and blue pixels.

[0060] In the case of a QD-LED panel, a single-color quantum dot layer such as white or blue may be overlaid with a color OLED layer or color filter including red OLED, green OLED, and blue OLED to form red pixels, green pixels, and blue pixels.

[0061] The pixel arrangement is not particularly limited, but may be a pentile arrangement in which the number of green pixels is twice the number of red pixels and blue pixels, or a real RGB arrangement in which red pixels, green pixels, and blue pixels are arranged in a 1:1:1 ratio.

[0062] (Circular polarizing element) The circular polarization element 20 converts the display light of the display panel 10 into circularly polarized light and transmits the light. The circular polarization element 20 of this embodiment includes a first linear polarizer 21 and a first quarter-wave plate 22. The first linear polarizer 21 converts the display light into linearly polarized light, and the first quarter-wave plate 22 converts the linearly polarized light into circularly polarized light.

[0063] The first linear polarizer 21 is not particularly limited as long as it transmits linearly polarized light having a specific vibration direction, and a polarizer commonly used in the field of display devices can be used. The linear polarizer may be either an absorptive type or a reflective type.

[0064] An absorptive polarizing plate has the function of absorbing light vibrating in a specific direction and transmitting polarized light vibrating in a direction perpendicular to that (linearly polarized light). The absorptive polarizing plate has a transmission axis and an absorption axis perpendicular to the transmission axis. An example of an absorptive linear polarizing plate is one in which a uniaxially stretched film of polyvinyl alcohol to which iodine compound molecules have been adsorbed is sandwiched between triacetyl cellulose (TAC).

[0065] A reflective polarizing plate has the function of reflecting light vibrating in a specific direction and transmitting polarized light vibrating in a direction perpendicular to that (linearly polarized light). A reflective polarizing plate has a transmission axis and a reflection axis perpendicular to the transmission axis. Examples of reflective linear polarizing plates include reflective polarizing plates obtained by uniaxially stretching a co-extruded film made of two types of resin (for example, APCF manufactured by Nitto Denko Corporation or DBEF manufactured by 3M), and wire grid polarizing plates in which thin metal wires are arranged. Examples of wire grid polarizing plates include those in which thin metal wires with a diameter of about 10 μm to 100 μm are arranged at a pitch of 20 μm to 200 μm.

[0066] The first quarter-wave plate 22 is not particularly limited as long as it is a retardation plate that imparts a quarter phase difference to incident light. The first quarter-wave plate 22 refers to a retardation plate that imparts an in-plane phase difference of a quarter wavelength (strictly speaking, 137.5 nm) to light with a wavelength of 550 nm, for example, and may be one that imparts an in-plane phase difference of 120 nm or more and 150 nm or less.

[0067] The circular polarizing element 20 may be a cholesteric liquid crystal element. When the circular polarizing element 20 is a cholesteric liquid crystal element, the cholesteric liquid crystal element converts the display light emitted from the display panel 10 into circularly polarized light.

[0068] In this specification, when light is observed in the direction opposite to the light propagation direction, right-handed circularly polarized light is defined as light whose electric displacement vector rotates clockwise as the light wave propagates, and left-handed circularly polarized light is defined as light whose electric displacement vector rotates counterclockwise as the light wave propagates. Circularly polarized light includes not only perfect circular polarization (ellipticity (minor axis / major axis) = 1.00) but also elliptically polarized light with an ellipticity of 0.90 or more and less than 1.00.

[0069] An example of a cholesteric liquid crystal element is one in which a cholesteric liquid crystal layer containing cholesteric liquid crystals is sandwiched between a pair of substrates. By performing an alignment treatment on the substrates and controlling the orientation of the cholesteric liquid crystal, it is possible to fabricate a cholesteric liquid crystal element that reflects circularly polarized light in one direction, either right-handed or left-handed, and transmits circularly polarized light in the other direction. The cholesteric liquid crystal layer can be fabricated with a thickness of several micrometers, allowing the display panel 10 and the half mirror 30 to be located closer to each other. The substrate on the viewer side of the display panel 10 may be used as a support base, and the cholesteric liquid crystal layer may be formed on the surface of the substrate on the viewer side of the display panel 10.

[0070] (half mirror) The half mirror 30 is an optical element that reflects a portion of incident light and transmits the remaining portion. The reflectance and transmittance of the half mirror 30 are not limited, but the half mirror 30, for example, reflects 30% to 70% of the incident light and transmits the remainder, and preferably reflects 50% and transmits 50%. The half mirror 30 can be made of, for example, a metal film or a dielectric multilayer film, and the transmittance and reflectance are controlled by the film thickness.

[0071] (lens) The surface of lens 40 facing circularly polarized light selective reflection element 50 is flat. In this specification, "flat" refers to a shape with a radius of curvature R of 150 mm or more. In addition, in this specification, "spherical" refers to a shape with a radius of curvature R of less than 150 mm.

[0072] There are no particular limitations on the lens 40 as long as it enlarges or reduces the image on the display panel 10. The combination of the lens 40 and the PB lens 40PB allows the viewer to view an enlarged image (virtual image) of the image displayed on the display panel 10. The combination of the lens 40 and the PB lens 40PB is preferably an aspherical lens designed to focus light transmitted through the combination of the lens 40 and the PB lens 40PB on the eye of the viewer U. The lens 40 may be a refractive lens or a diffractive lens.

[0073] The refractive lens may be one commonly used in the field of HMDs, such as a plano-convex lens, a biconvex lens, or a meniscus lens, which has a curved (convex) surface. A Fresnel lens may also be used. The refractive lens is preferably arranged so that its convex surface faces the display panel 10. The refractive lens may be an achromatic lens formed by bonding two lenses with different wavelength dispersions together, or a combination of multiple lenses. For example, an optical system using two lenses is generally used to obtain appropriate lens power. It is conceivable to use a biconvex lens as the lens closer to the display device, and a convex-plano lens as the lens closer to the viewer, with the panel side being a convex Fresnel lens.

[0074] Examples of diffractive lenses include transmission-type holographic optical elements. Transmission-type holographic optical elements used as diffractive lenses can form an image on the display panel 10 by utilizing the above-mentioned light diffraction phenomenon. Hologram films can be used that have desired optical properties achieved by interference exposure using light corresponding to incident light and outgoing light. In addition, a method known as CGH (Computer Generated Hologram) has recently become available for manufacturing hologram films, in which desired optical properties are achieved by exposing small areas at a time.

[0075] (PB lens) The display device 100 of this embodiment includes a PB lens 40PB between the lens 40 and the circularly polarized light selective reflection element 50. The PB lens 40PB focuses incident left-handed or right-handed circularly polarized light and diverges incident right-handed circularly polarized light. This configuration improves the display characteristics of the folded optical system display device 100. For example, better image quality optimization is possible in the folded optical system, and an optical system with a particularly wide FOV (Field Of View) can be realized. The PB lens 40PB is also called a PBP (Pancharatnam Berry phase) lens. The PB lens 40PB is a diffractive lens.

[0076] In this embodiment, instead of making the surface of the lens facing the circularly polarized light selective reflection element spherical, a PB lens 40PB is used, which is a diffractive lens that can bend light on a flat surface. When left-handed or right-handed circularly polarized light is incident on the PB lens 40PB, the PB lens 40PB has the function of converging the one circularly polarized light while rotating it in the opposite direction, and when the other circularly polarized light is incident on the PB lens 40PB, the PB lens 40PB has the function of diverging the other circularly polarized light while rotating it in the opposite direction.

[0077] Fig. 2 is a schematic plan view of a PB lens. As shown in Fig. 2, the PB lens 40PB of this embodiment includes a support substrate 410 and periodically oriented liquid crystal molecules 420 provided on the support substrate 410. The periodic orientation of the liquid crystal molecules 420 causes diffraction, thereby providing a lens function.

[0078] Fig. 3 is a schematic diagram illustrating an example of light collection and divergence of a PB lens. As shown in Fig. 3, for example, when one of left-handed and right-handed circularly polarized light is incident on the PB lens 40PB, the PB lens 40PB collects the one circularly polarized light while rotating it in the opposite direction and converting it into the other circularly polarized light, and when the other circularly polarized light is incident on the PB lens 40PB, the PB lens 40PB diverges the other circularly polarized light while rotating it in the opposite direction and converting it into one circularly polarized light.

[0079] Specifically, as shown in FIG. 3, right-handed circularly polarized light ((i) in FIG. 3) incident on the PB lens 40PB is rotated in the opposite direction and converted into left-handed circularly polarized light, which is then focused ((ii) in FIG. 3). Also, left-handed circularly polarized light ((iii) in FIG. 3) incident on the PB lens 40PB is rotated in the opposite direction and converted into right-handed circularly polarized light, which is then diverged ((iv) in FIG. 3). In this way, by switching the rotation direction of the circularly polarized light incident on the PB lens 40PB, it is possible to switch between divergence and focusing at the focal point f. Also, the rotation direction of the circularly polarized light emitted from the PB lens 40PB is opposite to the rotation direction of the circularly polarized light incident on the PB lens 40PB. Note that light that is not diffracted does not change its direction of circular polarization, and passes through as is without focusing or diverging ((v) in FIG. 3).

[0080] FIGS. 4 and 5 are each an example of an exploded cross-sectional view of a display device according to the first embodiment. The display device 100 of this embodiment includes two types shown in FIGS. 4 and 5, depending on the divergence and concentration directions of the PB lens 40PB. FIG. 4 illustrates a configuration in which light irradiated from the display panel 10 is diverged twice and concentrated once by the PB lens 40PB before being output toward the viewer U. FIG. 5 illustrates a configuration in which light irradiated from the display panel 10 is concentrated twice and diverged once by the PB lens 40PB before being output toward the viewer U. Here, the rotation direction of the liquid crystal molecules of the PB lens differs depending on whether the PB lens is observed from the front or rear surface. For example, if the liquid crystal molecules are aligned with a counterclockwise rotation when the PB lens is observed from the front surface, the liquid crystal molecules are aligned with a clockwise rotation when the PB lens is observed from the rear surface. In other words, if right-handed circularly polarized light incident from the front surface of the PB lens diverges, right-handed circularly polarized light incident from the rear surface of the PB lens will be focused.

[0081] It is preferable that the light emitted from the display panel 10 is diverged twice and converged once by the PB lens 40PB before being emitted toward the viewer U. By adopting such an embodiment, the display characteristics can be effectively improved.

[0082] 6 and 7 are plan views showing an example of a PB lens. The plan views shown in Fig. 6 and 7 are plan views seen from the side of an observer U. There are two types of PB lenses 40PB: one with a structure in which the long axes 420X of the liquid crystal molecules 420 rotate counterclockwise from the center to the outside, as shown in Fig. 6, and one with a structure in which the long axes 420X of the liquid crystal molecules 420 rotate clockwise from the center to the outside, as shown in Fig. 7, and these have different effects on polarized light.

[0083] 6, the PB lens 40PB includes a support substrate 410 and liquid crystal molecules 420 provided on the support substrate 410, and the long axes 420X of the liquid crystal molecules 420 have a structure in which, when the PB lens 40PB is viewed in plan from the viewer U side, the long axes 420X rotate counterclockwise from the center of the PB lens 40PB toward the outside, and it is preferable that right-handed circularly polarized light is incident on the PB lens 40PB from the display panel 10. By adopting such an embodiment, as shown in FIG. 4, light irradiated from the display panel 10 is diverged twice and focused once by the PB lens 40PB before being emitted toward the viewer U side.

[0084] 7, the PB lens 40PB includes a support substrate 410 and liquid crystal molecules 420 provided on the support substrate 410, and the long axes 420X of the liquid crystal molecules 420 have a structure in which they rotate clockwise from the center of the PB lens 40PB toward the outside when the PB lens 40PB is viewed in plan from the viewer U side, and it is also preferable that left-handed circularly polarized light is incident on the PB lens 40PB from the display panel 10. Even with this configuration, the light irradiated from the display panel 10 is diverged twice and focused once by the PB lens 40PB before being emitted toward the viewer U side.

[0085] 6, the PB lens 40PB includes a support substrate 410 and liquid crystal molecules 420 provided on the support substrate 410, and has a structure in which the long axes 420X of the liquid crystal molecules 420 rotate counterclockwise from the center of the PB lens 40PB toward the outside when the PB lens 40PB is viewed in plan from the viewer U side, and left-handed circularly polarized light may be incident on the PB lens 40PB from the display panel 10. With this configuration, light irradiated from the display panel 10 is collected twice and diverged once by the PB lens 40PB before being emitted toward the viewer U side.

[0086] 7, the PB lens 40PB includes a support substrate 410 and liquid crystal molecules 420 provided on the support substrate 410, and has a structure in which the long axes 420X of the liquid crystal molecules 420 rotate clockwise from the center of the PB lens 40PB toward the outside when the PB lens 40PB is viewed in plan from the viewer U side, and right-handed circularly polarized light may be incident on the PB lens 40PB from the display panel 10. Even with this configuration, light irradiated from the display panel 10 is collected twice and diverged once by the PB lens 40PB, and then emitted toward the viewer U side.

[0087] Here, the rotation direction of the circularly polarized light incident on the PB lens 40PB can be controlled by interchanging the fast axis and slow axis of the first quarter-wave plate 22.

[0088] The PB lens 40PB can be produced, for example, by the method described in International Publication No. 2019 / 189818.

[0089] Fig. 8 is an example of a cross-sectional schematic diagram of a PB lens included in the display device of embodiment 1. As shown in Fig. 8, the PB lens 40PB includes an optically anisotropic layer 420A containing liquid crystal molecules 420. As an example, the PB lens 40PB diffracts and transmits circularly polarized light incident thereon in a predetermined direction. Note that in Fig. 8, the incident light is left-handed circularly polarized light.

[0090] As shown in Fig. 8, the optically anisotropic layer 420A has three regions R0, R1, and R2 from the left side in Fig. 8, and the length Λ of one period differs in each region. Specifically, the length Λ of one period becomes shorter in the order of regions R0, R1, and R2. Furthermore, regions R1 and R2 may have a structure in which the optical axis is twisted and rotated in the thickness direction of the optically anisotropic layer (hereinafter also referred to as a twisted structure). By stacking two layers of such twisted structures, it is possible to improve diffraction efficiency over a wide wavelength range and incident angle.

[0091] In the display device 100, when left-handed circularly polarized light LC1 enters region R1 in the plane of the optically anisotropic layer 420A, it is diffracted at a predetermined angle in the direction of arrow X with respect to the incident direction, i.e., in one direction in which the orientation of the optical axes of the liquid crystal molecules 420 changes while continuously rotating, and then transmitted. Similarly, when left-handed circularly polarized light LC2 enters region R2 in the plane of the optically anisotropic layer 420A, it is diffracted at a predetermined angle in the direction of arrow X with respect to the incident direction and then transmitted. Similarly, when left-handed circularly polarized light LC0 enters region R0 in the plane of the optically anisotropic layer 420A, it is diffracted at a predetermined angle in the direction of arrow X with respect to the incident direction and then transmitted.

[0092] The angle of diffraction by the optically anisotropic layer 420A is one period Λ of the liquid crystal alignment pattern in the region R1. R1 than one period Λ of the liquid crystal alignment pattern in region R2 R2 Since the distance is short, the angle of diffraction for the incident light is the angle θ R2 The angle θ of the transmitted light in the region R1 R1 In addition, one period Λ of the liquid crystal alignment pattern in the region R1 R1 than one period Λ of the liquid crystal alignment pattern in the region R0 R0 Since the angle of diffraction for the incident light is long, as shown in Figure 8, the angle of the transmitted light in the region R0 is R0 The angle θ of the transmitted light in the region R1 R1 will be smaller than

[0093] Here, in the diffraction of light by an optically anisotropic layer having a liquid crystal orientation pattern in which the orientation of the optical axes of the liquid crystal molecules changes while continuously rotating within the plane, there is a problem that the diffraction efficiency decreases as the diffraction angle increases, that is, the intensity of the diffracted light weakens. Therefore, if the optically anisotropic layer is configured to have regions where the length of one period in which the orientation of the optical axes of the liquid crystal molecules rotates 180° within the plane varies, the diffraction angle varies depending on the position of incidence of light, resulting in a difference in the amount of diffracted light depending on the position of incidence within the plane. In other words, depending on the position of incidence within the plane, there will be regions where the transmitted and diffracted light is dark.

[0094] In contrast, the PB lens 40PB of this embodiment has a region where the optically anisotropic layer twists and rotates in the thickness direction, and has regions with different twist angles in the thickness direction. In the example shown in Figure 8, the twist angle φ in the thickness direction of region R2 of the optically anisotropic layer 420A is R2 is the twist angle φ in the thickness direction of region R1 R1 Furthermore, the region R0 does not have a twisted structure in the thickness direction, which makes it possible to suppress a decrease in the diffraction efficiency of diffracted light.

[0095] In the example shown in Fig. 8, by providing a twisted structure to regions R1 and R2, which have a larger diffraction angle than region R0, it is possible to suppress a decrease in the amount of light diffracted in regions R1 and R2. Furthermore, by making the twisted angle of the twisted structure in region R2, which has a larger diffraction angle than region R1, larger than that of region R1, it is possible to suppress a decrease in the amount of light diffracted in region R2. This makes it possible to make the amount of transmitted light uniform depending on the incident position within the plane.

[0096] Thus, in the PB lens 40PB of this embodiment, in in-plane regions where the diffraction by the optically anisotropic layer is large, incident light passes through a layer with a large twist angle in the thickness direction and is diffracted. In contrast, in in-plane regions where the diffraction by the optically anisotropic layer is small, incident light passes through a layer with a small twist angle in the thickness direction and is diffracted. That is, in the PB lens 40PB, by setting the in-plane twist angle in the thickness direction according to the magnitude of diffraction by the optically anisotropic layer, it is possible to brighten the transmitted light relative to the incident light. Therefore, the PB lens 40PB can reduce the diffraction angle dependence of the amount of transmitted light in the plane.

[0097] The angle of diffracted light in the plane of the optically anisotropic layer 420A increases as the period Λ of the liquid crystal orientation pattern decreases. The twist angle in the thickness direction in the plane of the optically anisotropic layer 420A is larger in a region with a short period Λ, where the optical axis rotates 180° along the direction of the arrow X in the liquid crystal orientation pattern, than in a region with a long period Λ. In the PB lens 40PB, as shown in FIG. 8, for example, the period Λ of the liquid crystal orientation pattern in region R2 of the optically anisotropic layer 420A is R2 is one period Λ of the liquid crystal alignment pattern in region R1. R1 shorter than the twist angle φ in the thickness direction R2 is the twist angle φ in the thickness direction R1 That is, the region R2 of the optically anisotropic layer 420A on the light incident side diffracts light to a large extent.

[0098] Therefore, by setting the in-plane twist angle φ in the thickness direction for one period Λ of the target liquid crystal orientation pattern, it is possible to suitably brighten the transmitted light diffracted at different angles in different regions in the plane.

[0099] In the PB lens 40PB, as described above, the shorter the period Λ of the liquid crystal orientation pattern, the larger the angle of diffraction, and therefore, the brighter the transmitted light can be achieved by increasing the twist angle in the thickness direction in regions where the period Λ of the liquid crystal orientation pattern is shorter. Therefore, in the PB lens 40PB, it is preferable to have regions where the permutation of the length of the period and the permutation of the magnitude of the twist angle in the thickness direction are different in regions where the length of the period of the liquid crystal orientation pattern is different.

[0100] The PB lens 40PB has an optically anisotropic layer 420A formed using a liquid crystal composition containing liquid crystal molecules 420, and the optically anisotropic layer 420A has a liquid crystal orientation pattern in which the direction of the optical axis derived from the liquid crystal molecules changes while continuously rotating along at least one direction in the plane, and has a region in which the optical axis twists and rotates in the thickness direction of the optically anisotropic layer 420A, and preferably has a region with a different magnitude of twist angle in the thickness direction.

[0101] When the length of an in-plane rotation of the optical axis direction originating from the liquid crystal molecules 420 is taken as one period, the PB lens 40PB preferably has regions where the length of one period in the liquid crystal orientation pattern varies.

[0102] In the optically anisotropic layer 420A, it is preferable that the multiple regions having different lengths of one period in the liquid crystal orientation pattern are arranged in the order of the lengths of the single period, and the multiple regions having different magnitudes of twist angles in the thickness direction are arranged in the order of the magnitudes of the twist angles in the thickness direction, and that the direction of the permutation of the lengths of the single period is different from the direction of the permutation of the magnitudes of the twist angles in the thickness direction.

[0103] The optically anisotropic layer 420A preferably has a region where the twist angle in the thickness direction is 10° to 360°.

[0104] In the optically anisotropic layer 420A, it is preferable that one period of the liquid crystal orientation pattern gradually becomes shorter toward the one direction in which the direction of the optical axis derived from the liquid crystal molecules 420 in the liquid crystal orientation pattern changes while continuously rotating.

[0105] The liquid crystal alignment pattern of the optically anisotropic layer 420A is preferably a concentric pattern extending from the inside to the outside in the one direction in which the orientation of the optical axis of the liquid crystal molecules 420 changes while continuously rotating.

[0106] 8 is a PB lens whose twist angle varies in-plane and is an element whose diffraction efficiency is high even when the diffraction angle is large, but the PB lens 40PB may be a PB lens whose twist angle does not vary in-plane. Specifically, the PB lens 40PB may be a PB lens that has no twist in the thickness direction or has a constant twist angle in-plane, and for example, the polarization diffraction grating described in JP2008-532085A can be used.

[0107] The PB lens 40PB is a PB lens having a plurality of optically anisotropic layers 420A, and preferably has optically anisotropic layers 420A whose twist angles in the thickness direction of the optically anisotropic layers 420A are different from each other.

[0108] The PB lens 40PB is a PB lens having a plurality of optically anisotropic layers 420A, and preferably has optically anisotropic layers 420A with different twist angles in the thickness direction of the optically anisotropic layers 420A.

[0109] The PB lens 40PB is a PB lens having multiple optically anisotropic layers 420A, and it is preferable that the optically anisotropic layers 420A have a liquid crystal orientation pattern in which the directions in which the optical axes derived from the liquid crystal molecules 420 continuously rotate along at least one direction in the plane are the same.

[0110] The length of one period in the liquid crystal alignment pattern is preferably 50 μm or less.

[0111] (Circularly polarized selective reflection element) The circularly polarized light selective reflection element 50 selectively reflects circularly polarized light that has passed through the PB lens 40PB. It is preferable that the circularly polarized light selective reflection element 50 transmits circularly polarized light that has the same rotation direction as the circularly polarized light that has passed through the circular polarization element 20, and reflects circularly polarized light that has the opposite rotation direction to the circularly polarized light that has passed through the circular polarization element 20. For example, if the circularly polarized light that has passed through the circular polarization element 20 is clockwise, the circularly polarized light selective reflection element 50 transmits the clockwise circularly polarized light and reflects the counterclockwise circularly polarized light.

[0112] The circularly polarized light selective reflection element 50 may include a laminate of a reflective linear polarizer 51 and a second quarter-wave plate 52. The reflective linear polarizer 51 may be the same as the reflective linear polarizer exemplified above as the circular polarization element 20. The second quarter-wave plate 52 may be the same as the first quarter-wave plate 22. The slow axis of the first quarter-wave plate 22 in the circular polarization element 20 and the slow axis of the second quarter-wave plate 52 in the circularly polarized light selective reflection element 50 are preferably orthogonal to each other.

[0113] The circularly polarized light selective reflection element 50 may be a cholesteric liquid crystal element. When the circularly polarized light selective reflection element 50 is a cholesteric liquid crystal element, the same cholesteric liquid crystal element as the above-mentioned exemplified circularly polarized light element 20 can be used. The light transmitted through the cholesteric liquid crystal element is circularly polarized light. When the circularly polarized light element 20 and the circularly polarized light selective reflection element 50 are both cholesteric liquid crystal elements, it is preferable that the direction of the transmitted circularly polarized light (clockwise or counterclockwise) be opposite between the cholesteric liquid crystal element serving as the circularly polarized light element 20 and the cholesteric liquid crystal element serving as the circularly polarized light selective reflection element 50.

[0114] It is preferable that circularly polarized light selective reflection element 50 is flat. This configuration can further improve productivity, such as reliability and yield. It is more preferable that the surface of circularly polarized light selective reflection element 50 facing PB lens 40PB is flat.

[0115] <Modification 1 of Embodiment 1> In this modification, features unique to this modification will be mainly described, and descriptions of details overlapping with those of the first embodiment will be omitted. FIG. 9 is an exploded schematic diagram illustrating a display device according to a first modification of the first embodiment. As shown in FIG. 9, the lens 40 included in the display device 100 of this modification includes a first lens unit 40A and a second lens unit 40B. This configuration also enables a folding optical system using a half mirror 30, thereby enabling the display device 100 to be made thinner. Furthermore, the lens power obtained when the surface of the lens 40 facing the circularly polarized light selective reflection element 50 is spherical can be imparted to the Pancharatnam Berry lens 40PB. This allows the surface of the lens 40 facing the circularly polarized light selective reflection element 50 to be planarized, thereby improving the display characteristics of the display device 100. Furthermore, since the surface of the lens 40 facing the circularly polarized light selective reflection element 50 is planarized, the circularly polarized light selective reflection element 50 can be easily bonded to the lens 40, thereby improving productivity. Furthermore, since the lens 40 includes the first lens portion 40A and the second lens portion 40B, it is possible to increase the lens power of the display device 100, and the display characteristics of the display device 100 can be further improved.

[0116] The lens 40 includes a first lens portion 40A and a second lens portion 40B. There are no particular limitations on the first lens portion 40A and the second lens portion 40B as long as they can enlarge or reduce the image on the display panel 10, and they may be refractive lenses or diffractive lenses.

[0117] <Modification 2 of Embodiment 1> In this modification, features unique to this modification will be mainly described, and descriptions of content overlapping with those of the above-described first embodiment will be omitted. FIG. 10 is an exploded schematic diagram illustrating a display device according to a second modification of the first embodiment. FIG. 11 is an exploded schematic diagram illustrating ghosts that may occur in the display device according to the first embodiment. As shown in FIG. 10, the display device 100 of this modification further includes an observer-side PB lens 41PB between the circularly polarized light selective reflection element 50 and the observer U. This configuration also makes it possible to realize a folding optical system using the half mirror 30, thereby enabling the display device 100 to be made thinner. Furthermore, the lens power obtained when the surface of the lens 40 facing the circularly polarized light selective reflection element 50 is spherical can be imparted to the Pancharatnam Berry lens 40PB, thereby improving the display characteristics of the display device 100 while making the surface of the lens 40 facing the circularly polarized light selective reflection element 50 flat. Furthermore, since the surface of lens 40 facing circularly polarized light selective reflection element 50 is flat, circularly polarized light selective reflection element 50 can be easily bonded to lens 40, thereby improving productivity.

[0118] Furthermore, the following effect can be obtained. Because the PB lens is a diffractive lens, it is difficult to achieve a diffraction efficiency of 100% unless the light source is a short-wavelength, narrow-directivity light source such as a laser. Therefore, in the display device 100 of embodiment 1, light that is not diffracted by the PB lens 40PB does not change its direction of circular polarization, and passes through as is without being focused or diverged ((xii) in FIG. 11). This may result in the occurrence of ghost images.

[0119] On the other hand, the display device 100 of this modified example is provided with the observer-side PB lens 41PB, so that the undiffracted light is not focused on the eyes of the observer U ((xii) of Figure 10). This makes it possible to prevent ghosts from being seen. In this way, by arranging the observer-side PB lens 41PB closer to the observer U than the PB lens 40PB, the light that is not diffracted as intended can be shifted in focus so that it is not seen by the eyes of the observer U.

[0120] The observer-side PB lens 41PB focuses circularly polarized light in the same direction as the PB lens 40PB, but the focal length of the observer-side PB lens 41PB does not have to be the same as the focal length of the PB lens 40PB.

[0121] <Embodiment 2> In this embodiment, features unique to this embodiment will be mainly described, and descriptions of content overlapping with those of the first embodiment will be omitted. FIG. 12 is an exploded schematic view showing a display device according to the second embodiment. As shown in FIG. 12, the lens 40 of the first embodiment is a first lens 40, and the circularly polarized light selective reflection element 50 of the first embodiment is a first circularly polarized light selective reflection element 50. The display device 100 of this embodiment further includes, between the display panel 10 and the half mirror 30, a second circularly polarized light selective reflection element 60, a display panel-side PB lens 42PB, and a second lens 41, in this order toward the viewer U, and the surface of the second lens 41 facing the second circularly polarized light selective reflection element 60 is flat. This configuration also makes it possible to realize a folded optical system using the half mirror 30, thereby enabling the display device 100 to be made thinner. Furthermore, since it is possible to impart to the PB lens 40PB the lens power that would be obtained if the surface of the first lens 40 facing the first circularly polarized light selective reflection element 50 were spherical, it is possible to improve the display characteristics of the display device 100 while making the surface of the first lens 40 facing the first circularly polarized light selective reflection element 50 flat. Furthermore, since the surface of the first lens 40 facing the first circularly polarized light selective reflection element 50 is flat, it is possible to easily bond the first circularly polarized light selective reflection element 50 to the first lens 40, thereby improving productivity.

[0122] Furthermore, since it is possible to impart to the display panel-side PB lens 42PB the lens power obtained when the surface of second lens 41 facing second circularly polarized light selective reflection element 60 is spherical, it is possible to improve the display characteristics of display device 100 while making the surface of second lens 41 facing second circularly polarized light selective reflection element 60 flat. Furthermore, since the surface of second lens 41 facing second circularly polarized light selective reflection element 60 is flat, it is possible to easily bond second circularly polarized light selective reflection element 60 to second lens 41, thereby improving productivity.

[0123] Furthermore, in addition to the first path RT1, which corresponds to the pancake lens system shown in the first embodiment, it is possible to utilize the light of the second path RT2, thereby improving the light utilization efficiency.

[0124] Since the images on the first path RT1 and the second path RT2 must overlap, it is preferable that the display device 100 basically has a symmetrical structure with the half mirror 30 as the center.

[0125] More specifically, the display device 100 of this embodiment comprises, in order toward the observer U side, a display panel 10, a first linear polarizer 21, a second circularly polarized light selective reflection element 60, a first quarter-wave plate 22, a display panel side PB lens 42PB, a second lens 41, a half mirror 30, a first lens 40, a PB lens 40PB, a second quarter-wave plate 23, and a first circularly polarized light selective reflection element 50.

[0126] The surface of second lens 41 facing second circularly polarized light selective reflection element 60 is flat. Second lens 41 is similar to first lens 40, except that the surface facing second circularly polarized light selective reflection element 60 is flat.

[0127] The display panel side PB lens 42PB is similar to the PB lens 40PB.

[0128] The second circularly polarized light selective reflection element 60 is similar to the first circularly polarized light selective reflection element 50. The second circularly polarized light selective reflection element 60 is preferably disposed between the first linear polarizer 21 and the first quarter-wave plate 22.

[0129] The second quarter-wave plate 23 is similar to the first quarter-wave plate 22. The slow axis of the first quarter-wave plate 22 and the slow axis of the second quarter-wave plate 23 are preferably orthogonal. In this specification, "two lines (including axes, directions, and orientations) are orthogonal" means that the angle (absolute value) between them is within a range of 90±3°, preferably within a range of 90±1°, more preferably within a range of 90±0.5°, and particularly preferably 90° (completely orthogonal). In this specification, "two lines (including axes, directions, and orientations) are parallel" means that the angle (absolute value) between them is within a range of 0±3°, preferably within a range of 0±1°, more preferably within a range of 0±0.5°, and particularly preferably 0° (completely parallel).

[0130] <Modification 1 of Embodiment 2> In this modification, features unique to this modification will be mainly described, and details overlapping with those of the second embodiment will not be described. FIG. 13 is an exploded schematic diagram illustrating a display device according to a first modification of the second embodiment. FIG. 14 is an exploded schematic diagram illustrating ghosts that may occur in the display device according to the second embodiment. As shown in FIG. 13, the display device 100 of this modification further includes an observer-side PB lens 41PB between the first circularly polarized light selective reflection element 50 and the observer U. This configuration also makes it possible to realize a folding optical system using the half mirror 30, thereby enabling the display device 100 to be made thinner. Furthermore, it is possible to impart to the PB lens 40PB the lens power obtained when the surface of the first lens 40 facing the first circularly polarized light selective reflection element 50 is spherical, thereby improving the display characteristics of the display device 100 while making the surface of the first lens 40 facing the first circularly polarized light selective reflection element 50 flat. Furthermore, since the surface of first lens 40 facing first circularly polarized light selective reflection element 50 is flat, first circularly polarized light selective reflection element 50 can be easily bonded to first lens 40, thereby improving productivity.

[0131] Furthermore, since it is possible to impart to the display panel-side PB lens 42PB the lens power obtained when the surface of second lens 41 facing second circularly polarized light selective reflection element 60 is spherical, it is possible to improve the display characteristics of display device 100 while making the surface of second lens 41 facing second circularly polarized light selective reflection element 60 flat. Furthermore, since the surface of second lens 41 facing second circularly polarized light selective reflection element 60 is flat, it is possible to easily bond second circularly polarized light selective reflection element 60 to second lens 41, thereby improving productivity.

[0132] Furthermore, in addition to the first path RT1, which corresponds to the pancake lens system shown in the first embodiment, it is possible to utilize the light of the second path RT2, thereby improving the light utilization efficiency.

[0133] Furthermore, the following effect can be obtained. Because the PB lens is a diffractive lens, it is difficult to achieve 100% diffraction efficiency unless the light source is a short-wavelength, narrow-directivity light source such as a laser. Therefore, in the display device 100 of embodiment 2, light that is not diffracted by the PB lens 40PB does not change its direction of circular polarization and passes through as is without being focused or diverged (light 3L in FIG. 14). This may result in ghosting.

[0134] On the other hand, because display device 100 of this modified example is equipped with observer-side PB lens 41PB, non-diffracted light is not focused on the eye of observer U (light 3L in FIG. 13). This makes it possible to prevent ghosts from being seen. In this way, by arranging observer-side PB lens 41PB closer to observer U than PB lens 40PB, it is possible to shift the focus of light that is not diffracted as intended so that it is not seen by observer U's eye.

[0135] <Embodiment 3> In this embodiment, features unique to this embodiment will be mainly described, and descriptions of contents overlapping with those of the above-mentioned Embodiment 1 and its modifications, and the above-mentioned Embodiment 2 and its modifications will be omitted. The display device of this embodiment uses a liquid crystal panel as a display panel. In this embodiment, the display panel is a liquid crystal panel including a pair of substrates and a liquid crystal layer sandwiched between the pair of substrates, and the circular polarization element includes a laminate of a first linear polarizer and a quarter-wave plate, and further includes a second linear polarizer on the side of the display panel opposite the circular polarization element. Descriptions of configurations overlapping with those of Embodiment 1 will be omitted.

[0136] Fig. 15 is an exploded cross-sectional view schematically showing a display device according to embodiment 3. As shown in Fig. 15, in a display device 100 according to this embodiment, a display panel (liquid crystal panel) 70 includes a pair of substrates 71 and 72 and a liquid crystal layer 73 sandwiched between the pair of substrates 71 and 72. The substrate 71 may be a TFT substrate 71, and the substrate 72 may be an opposing substrate 72.

[0137] As exemplified in embodiment 1, the TFT substrate 71 may have, on a support substrate, a plurality of gate lines extending parallel to one another, a plurality of source lines extending parallel to one another in a direction intersecting each gate line via a gate insulating film, and a plurality of TFTs arranged for each pixel at the intersection of each gate line and each source line.

[0138] The display mode of the liquid crystal panel is not particularly limited, and it may be a liquid crystal panel of horizontal alignment (horizontal electric field) mode in which the counter electrode is provided on the TFT substrate 71, or a vertical alignment (vertical electric field) mode in which the counter electrode is provided on the counter substrate 72 with the liquid crystal layer 73 sandwiched therebetween.

[0139] Fig. 16 is a schematic plan view of the liquid crystal panel shown in Fig. 15. The counter substrate 72 may be a color filter (CF) substrate including a support substrate and a black matrix and a CF layer formed on the support substrate.

[0140] 16, the CF substrate may have a configuration in which, for example, color filters 74 are arranged in a plane and partitioned by a black matrix 75. The color filters 74 may include a red color filter 74R, a green color filter 74G, and a blue color filter 74B. The color filters 74 may be arranged in a stripe pattern in which red, green, and blue color filters are repeatedly arranged in the row direction and color filters 74R, 74G, and 74B of the same color are arranged in the column direction. Pixels overlapping with the red, green, and blue color filters 74R, 74G, and 74B become red, blue, and green pixels, respectively.

[0141] The black matrix 75 may be one that is commonly used in the field of liquid crystal panels, and may be made of a resin containing a black pigment, for example. The black matrix 75 may be provided in a lattice shape so as to overlap the gate lines and / or source lines in a plan view.

[0142] The liquid crystal layer 73 contains liquid crystal molecules. When a voltage is applied between the common electrode and the pixel electrode, an electric field is generated in the liquid crystal layer 73, and the orientation of the liquid crystal molecules changes in response to the electric field, thereby controlling the amount of light transmission. The orientation direction of the liquid crystal molecules when no voltage is applied is controlled by the restricting force of the alignment film. The above-mentioned "when no voltage is applied" refers to the case where no voltage is applied between the pair of electrodes in the liquid crystal layer 73, or where a voltage below the threshold value of the liquid crystal molecules is applied.

[0143] The liquid crystal molecules may have a positive or negative dielectric anisotropy (Δε) defined by the following formula: Δε = (dielectric constant in the long axis direction) - (dielectric constant in the short axis direction)

[0144] An alignment film may be provided between the TFT substrate 71 and the liquid crystal layer 73, and between the counter substrate 72 and the liquid crystal layer 73. When no voltage is applied to the liquid crystal layer 73, the alignment of the liquid crystal molecules is controlled mainly by the action of the alignment film. For example, in the horizontal alignment mode, the tilt angle (pretilt angle) of the liquid crystal molecules when no voltage is applied may be 0 to 5°, preferably 0 to 3°, and more preferably 0 to 1°. The tilt angle of the liquid crystal molecules refers to the angle at which the long axis (optical axis) of the liquid crystal molecules is inclined relative to the surfaces of the TFT substrate 71 and the counter substrate 72.

[0145] The second linear polarizer 80 is disposed on the opposite side of the liquid crystal panel 70 from the circular polarizer 20 (opposite side of the liquid crystal panel 70 from the viewer U). They are preferably disposed in a crossed Nicol state so that the transmission axis of the first linear polarizer 21 and the transmission axis of the second linear polarizer 80 are perpendicular to each other. The second linear polarizer 80 may be the same as the first linear polarizer 21.

[0146] Taking the normally black mode as an example, when no voltage is applied, the alignment direction of the liquid crystal molecules is aligned approximately parallel to either the transmission axis of the first linear polarizer 21 or the second linear polarizer 80 in a planar view. Light incident from the back of the liquid crystal panel passes through the second linear polarizer 80 and becomes linearly polarized light. This linearly polarized light passes through the liquid crystal layer 73 but does not pass through the first linear polarizer 21, resulting in the liquid crystal panel displaying black. On the other hand, when a voltage is applied to the liquid crystal layer 73, the alignment direction of the liquid crystal molecules changes from the initial alignment direction, and the long axis direction of the liquid crystal molecules forms an angle with the transmission axis of the first linear polarizer 21 and the second linear polarizer 80, causing the light to pass through the first linear polarizer 21 and the liquid crystal panel to display white.

[0147] In this embodiment, linearly polarized light that has passed through the first linear polarizer 21 is converted into circularly polarized light by passing through the quarter-wave plate 22. When the above-described cholesteric liquid crystal element is used as the circular polarizer, light reflected by the cholesteric liquid crystal element becomes stray light, which can cause the image to appear unclear and degrade the display quality of the liquid crystal panel. Therefore, in this embodiment, in which a liquid crystal panel is used as the display panel 10, it is preferable to use a laminate of the first linear polarizer 21 and the quarter-wave plate 22 as the circular polarizer.

[0148] (backlight) The display device 100 of this embodiment may further include a backlight including a light source on the side of the second linear polarizer 80 opposite to the liquid crystal panel 70.

[0149] The backlight may be a direct type or an edge-lit type. A direct-lit backlight has a light source disposed on the back surface of the liquid crystal panel. An edge-lit backlight has a light guide plate disposed on the back surface of the liquid crystal panel and a light source disposed on the side surface of the light guide plate. An edge-lit backlight causes light from the light source to enter the side surface of the light guide plate and emits the light from the light guide plate toward the liquid crystal panel. A reflective sheet may be disposed on the back surface of the light guide plate, and a prism sheet, a diffusion sheet, or the like may be disposed between the light guide plate and the display device 100.

[0150] The backlight preferably condenses light emitted from the light source in a direction along the thickness direction of the liquid crystal panel. The half width (full angle) of the backlight may be 15° to 30°. The half width can be determined by measuring the luminance viewing angle characteristic using a method in accordance with IEC61747-30, and by defining the angle range in which the luminance is at least half of the maximum luminance.

[0151] <Embodiment 4> In this embodiment, features unique to this embodiment will be mainly described, and descriptions of content that overlaps with the above-described embodiment 1 will be omitted. Fig. 17 is a schematic perspective view showing an example of the appearance of a head-mounted display of embodiment 4. As shown in Fig. 17, the head-mounted display 200 of this embodiment includes a display device 100 and a wearing unit 210 that is worn on the head of a viewer U. The head-mounted display 200 of this embodiment may be an immersive HMD in which the eyes of the viewer U are placed in a space that is shielded from external light when worn, or may be a glasses-type HMD.

[0152] The display device 100 has a function for displaying a video (image) to the observer U. The display device 100 converts a video display signal into a video.

[0153] When the head-mounted display 200 is an eyeglass-type HMD, as shown in FIG. 17, the part corresponding to the lens of eyeglasses is the display device 100, and the wearing part 210 may be the frame of the eyeglasses that the viewer U wears over their ears.

[0154] If the head-mounted display 200 is an immersive HMD, the wearing unit 210 may include a wearing band that goes around the head of the observer U when worn by the observer U and secures the head-mounted display 200 to the observer U's head.

[0155] The head mounted display 200 may be a single display type in which one display panel is arranged for each eye, or a dual display type in which one display panel is arranged for each eye. The immersive HMD can be applied to, for example, the single display type and the dual display type. The eyeglass-type HMD can be applied to, for example, the dual display type.

[0156] The head mounted display 200 may further include a face cushion 220 arranged between the display device 100 and the face of the observer U. The face cushion 220 is a buffer material arranged between the display device 100 and the face of the observer U, and by placing the face cushion 220, it is possible to prevent external light from entering the field of view of the observer U while the head mounted display 200 is in use.

[0157] The head mounted display 200 may further include an audio output unit having a function of generating sounds such as voice, music, and sound effects.

[0158] The acoustic output unit converts an acoustic output signal into sound. Usually, a commercially available headphone can be used. The acoustic output unit, together with the wearing unit 210, may function as a contact unit for the ear when the head mounted display 200 is worn on the head of the observer U.

[0159] The head mounted display 200 may also include a drive unit that outputs a video display signal and an audio output signal. The drive unit is connected to the display device 100 and the audio output unit by wire or wirelessly. An example of a wireless communication method is Bluetooth (registered trademark). [Example]

[0160] The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0161] <Comparative Example 1> A simulation was performed using optical design software on a display device 100R of Comparative Example 1 corresponding to the above-described comparative embodiment to verify whether the surface on which the circularly polarized light selective reflection element 50 is attached is flat. FIG. 18 is an exploded schematic diagram and a simulation diagram showing the display device of Comparative Example 1. FIG. 19 is an enlarged view of the area surrounded by the dashed line in FIG. 18. FIG. 20 is a diagram showing details of the simulation results for the display device of Comparative Example 1. FIGS. 18 to 20 show light 1LR, light 1LY, light 1LG, and light 1LB, each of which has a different angle Y at which light enters the eye. The angle Y at which light 1LR enters the eye is 10°, the angle Y at which light 1LY enters the eye is 20°, the angle Y at which light 1LG enters the eye is 45°, and the angle Y at which light 1LB enters the eye is 0°. The paths taken by light 1LR, light 1LY, light 1LG, and light 1LB were determined by simulation. The angle Y at which light enters the eye is determined based on the horizontal direction (0°) when the observer U views the display device 100 from the front. In other words, the angle Y at which light enters the eye is the angle between the horizontal direction when the observer U views the display device 100 from the front and the light entering the eye.

[0162] 18, the lens 40R included in the display device 100R of Comparative Example 1 included a first lens portion 40RA arranged on the display panel 10 side and a second lens portion 40RB arranged on the circularly polarized light selective reflection element 50 side. Here, the first lens portion 40RA and the second lens portion 40RB were the same as the first lens portion 40A and the second lens portion 40B, respectively. While it is basically ideal to perform a simulation for a configuration in which the lens 40R is made up of a single lens portion, in this comparative example, a simulation was performed for a configuration in which the lens 40R included the first lens portion 40RA and the second lens portion 40RB in order to further increase the lens power.

[0163] The first linear polarizer 21 and the first quarter-wave plate 22 included in the display device 100R of Comparative Example 1 were attached to the display panel 10, but are omitted from the lower diagram of FIG. 18 and FIG. 20. Of the two lens portions (first lens portion 40RA and second lens portion 40RB) included in the lens 40R, a half mirror 30 was attached to the left surface (surface facing the display panel 10) of the left lens portion (first lens portion 40RA) (closer to the display panel 10). Of the two lens portions (first lens portion 40RA and second lens portion 40RB), a circularly polarized light selective reflection element 50 was attached to the right surface (surface facing the circularly polarized light selective reflection element 50) of the right lens portion (second lens portion 40RB) (closer to the circularly polarized light selective reflection element 50).

[0164] As a result of the simulation, as shown in Fig. 20, the diameter of the display panel 10 was 45.1 mm. The gap between the center of the first lens portion 40RA and the center of the second lens portion 40RB was 1.0 mm. The gap between the center of the first lens portion 40RA and the center of the display panel 10 was 16.7 mm.

[0165] First lens portion 40RA had a thickness of 8.0 mm and a diameter of 49.9 mm. The radius of curvature of first lens portion 40RA near the center on the display panel 10 side was 5000 mm, and the radius of curvature of first lens portion 40RA near the center on the circularly polarized light selective reflection element 50 side was 67 mm.

[0166] Second lens portion 40RB had a thickness of 4.4 mm and a diameter of 50.0 mm. The radius of curvature of second lens portion 40RB near the center on the display panel 10 side was 122 mm, and the radius of curvature of second lens portion 40RB near the center on the circularly polarized light selective reflection element 50 side was 140 mm. That is, in Comparative Example 1, the surface to which circularly polarized light selective reflection element 50 was attached (specifically, the surface of lens 40R facing the circularly polarized light selective reflection element 50) needed to be spherical.

[0167] As described above, in display device 100R of Comparative Example 1, the lens surface closest to circularly polarized light selective reflection element 50 (the lens surface of second lens portion 40RB facing circularly polarized light selective reflection element 50) had to have a central radius of curvature of 140 mm and be spherical. Therefore, it is considered difficult to attach circularly polarized light selective reflection element 50 to lens 40R.

[0168] Example 1 A simulation was performed using optical design software similar to that of Comparative Example 1 for the display device 100 of Example 1, which corresponds to Modification 1 of Embodiment 1 described above, to verify whether the surface to which the circularly polarized light selective reflection element 50 is attached is flat. FIG. 21 is an exploded schematic view and a simulation diagram showing the display device of Example 1. FIG. 22 is an enlarged view of the area surrounded by the dashed line in FIG. 21. FIG. 23 is a diagram showing details of the simulation results for the display device of Example 1. FIGS. 21 to 23 show light 1LR, light 1LY, light 1LG, light 1LB, light 1LP, and light 1LW, each of which has a different angle Y at which light enters the eye. Light 1LR enters the eye at an angle Y of 10°, light 1LY enters the eye at an angle Y of 35°, light 1LG enters the eye at an angle Y of 5°, light 1LB enters the eye at an angle Y of 0°, light 1LP enters the eye at an angle Y of 45°, and light 1LW enters the eye at an angle Y of 20°. The routes taken by light 1LR, light 1LY, light 1LG, light 1LB, light 1LP, and light 1LW were determined by simulation.

[0169] 21 , the lens 40 included in the display device 100 of Example 1 included a first lens portion 40A arranged on the display panel 10 side and a second lens portion 40B arranged on the circularly polarized light selective reflection element 50 side. While it is basically ideal to perform a simulation for a configuration in which the lens 40 is made up of a single lens portion, in this example, a simulation was performed for a configuration in which the lens 40 includes the first lens portion 40A and the second lens portion 40B in order to further increase the lens power.

[0170] The first linear polarizer 21 and the first quarter-wave plate 22 included in the display device 100 of Example 1 were attached to the display panel 10, but are omitted from the lower diagram of FIG. 21 , FIGS. 22 and 23. Of the two lens portions (first lens portion 40A and second lens portion 40B) included in the lens 40, a half mirror 30 was attached to the left surface (surface facing the display panel 10) of the left lens portion (first lens portion 40A) (closer to the display panel 10). Of the two lens portions (first lens portion 40A and second lens portion 40B), a circularly polarized light selective reflection element 50 was attached to the right surface (surface facing the circularly polarized light selective reflection element 50) of the right lens portion (second lens portion 40B) (closer to the circularly polarized light selective reflection element 50).

[0171] As a result of the simulation, as shown in Fig. 23, the diameter of the display panel 10 was 49.5 mm. The gap between the center of the first lens portion 40A and the center of the second lens portion 40B was 1.4 mm. The gap between the center of the first lens portion 40A and the center of the display panel 10 was 1.7 mm.

[0172] First lens portion 40A had a thickness of 8.0 mm and a diameter of 49.3 mm. The radius of curvature of first lens portion 40A near the center on the display panel 10 side was 5000 mm, and the radius of curvature of first lens portion 40A near the center on the circularly polarized light selective reflection element 50 side was 67 mm.

[0173] The thickness of the second lens unit 40B was 1.8 mm, and the thickness of the PB lens 40PB was 0.5 mm. The diameter of the lens group consisting of the second lens unit 40B and the PB lens 40PB was 48.4 mm. The radius of curvature of the lens group near the center on the display panel 10 side was 122 mm, and the radius of curvature of the lens group near the center on the circularly polarized light selective reflection element 50 side was ∞ mm. That is, in Example 1, it was found that the lens shape on the circularly polarized light selective reflection element 50 side of the lens group consisting of the second lens unit 40B and the PB lens 40PB was planar. Here, since the main surface of the PB lens 40PB was planar, it can be said that the surface of the lens 40 (more specifically, the second lens unit 40B) facing the circularly polarized light selective reflection element 50 was planar. Thus, in Example 1, it was found that the surface to which the circularly polarized light selective reflection element 50 was attached (specifically, the surface of the lens 40 facing the circularly polarized light selective reflection element 50) was planar.

[0174] As described above, in Example 1 using PB lens 40PB, it was possible to obtain substantially the same characteristics as Comparative Example 1, while making it possible to make the lens surface closest to circularly polarized light selective reflection element 50 (the lens surface of the lens group facing circularly polarized light selective reflection element 50, more specifically, the lens surface of lens 40 facing circularly polarized light selective reflection element 50) flat. In other words, by disposing PB lens 40PB between lens 40 and circularly polarized light selective reflection element 50, the lens surface to which circularly polarized light selective reflection element 50 is attached can be made flat rather than spherical, making it possible to easily attach circularly polarized light selective reflection element 50 to lens 40, and it is thought that this can improve productivity.

[0175] Furthermore, the display device 100 of this embodiment is a folding optical system using a half mirror 30, which has made it possible to achieve a thin display device 100. Furthermore, it is possible to impart to the PB lens 40PB the lens power that is obtained when the surface of the lens 40 facing the circularly polarized light selective reflection element 50 is made spherical, and therefore it is possible to improve the display characteristics of the display device 100 while making the surface of the lens 40 facing the circularly polarized light selective reflection element 50 flat.

[0176] <Example 2> The display device of this example corresponds to the display device 100 of the first embodiment. As in the first example, the display device 100 of this example is a folding optical system using a half mirror 30, and the display device 100 can be made thinner. Furthermore, the lens power obtained when the surface of the lens 40 facing the circularly polarized light selective reflection element 50 is made spherical can be imparted to the PB lens 40PB, so the display characteristics of the display device 100 can be improved while the surface of the lens 40 facing the circularly polarized light selective reflection element 50 is made flat. Furthermore, since the surface of the lens 40 facing the circularly polarized light selective reflection element 50 is flat, the circularly polarized light selective reflection element 50 can be easily bonded to the lens 40, which is thought to improve productivity.

[0177] On the other hand, in the display device 100 of this embodiment, ghost images may be visible. Because the PB lens 40PB is a diffractive lens, it is difficult to achieve 100% diffraction efficiency for all light (obliquely incident light, all visible light wavelength range). For example, as shown in (xii) of FIG. 11, non-diffracted light may pass through without being focused or diverged, and circularly polarized light may not become reverse circularly polarized light. This is thought to be the cause of the ghost images.

[0178] Example 3 The display device of this example corresponds to the display device 100 of Modification 2 of Embodiment 1 above. As with Example 1 above, the display device 100 of this example is a folded optical system using a half mirror 30, and the display device 100 can be made thinner. Furthermore, it is possible to impart to the PB lens 40PB the lens power that would be obtained if the surface of the lens 40 facing the circularly polarized light selective reflection element 50 were spherical, thereby improving the display characteristics of the display device 100 while making the surface of the lens 40 facing the circularly polarized light selective reflection element 50 flat. Furthermore, since the surface of the lens 40 facing the circularly polarized light selective reflection element 50 is flat, it is possible to easily bond the circularly polarized light selective reflection element 50 to the lens 40, which is thought to improve productivity.

[0179] Furthermore, in this embodiment, it is possible to prevent ghost images from being seen. Here, the light that is not diffracted by the PB lens 40PB passes through the circularly polarized light selective reflection element 50 because its polarization state is different from the intended state. However, in the display device 100 of this embodiment, by arranging the observer-side PB lens 41PB between the circularly polarized light selective reflection element 50 and the observer U, the light that passes through via the correct path is focused on the eyes of the observer U, and the light that causes the ghost image is not focused on the eyes of the observer U, which is thought to prevent the ghost image from being seen.

[0180] Example 4 The display device of this example corresponds to the display device 100 of the above-described embodiment 2. As in the above-described embodiment 1, the display device 100 of this example is a folding optical system using a half mirror 30, and the display device 100 can be made thinner. Furthermore, it is possible to impart to the PB lens 40PB the lens power obtained when the surface of the first lens 40 facing the first circularly polarized light selective reflection element 50 is made spherical, and therefore the display characteristics of the display device 100 can be improved while the surface of the first lens 40 facing the first circularly polarized light selective reflection element 50 is made flat. Furthermore, since the surface of the first lens 40 facing the first circularly polarized light selective reflection element 50 is flat, it is possible to easily bond the first circularly polarized light selective reflection element 50 to the first lens 40, which is thought to improve productivity.

[0181] Furthermore, it is possible to impart to the display panel-side PB lens 42PB the lens power obtained when the surface of second lens 41 facing the second circularly polarized light selective reflection element 60 is spherical, thereby improving the display characteristics of display device 100 while making the surface of second lens 41 facing the second circularly polarized light selective reflection element 60 flat. Furthermore, since the surface of second lens 41 facing the second circularly polarized light selective reflection element 60 is flat, it is possible to easily bond second circularly polarized light selective reflection element 60 to second lens 41, which is thought to improve productivity.

[0182] Furthermore, as shown in FIG. 12, it becomes possible to use light on the second path RT2 in addition to the light on the first path RT1, thereby improving the light utilization efficiency.

[0183] <Example 5> The display device of this example corresponds to the display device 100 of Modification 1 of Embodiment 2 described above. As in Example 4 described above, the display device 100 of this example is a folded optical system using a half mirror 30, and the display device 100 can be made thinner. Furthermore, it is possible to impart to the PB lens 40PB the lens power obtained when the surface of the first lens 40 facing the first circularly polarized light selective reflection element 50 is made spherical, thereby improving the display characteristics of the display device 100 while making the surface of the first lens 40 facing the first circularly polarized light selective reflection element 50 flat. Furthermore, since the surface of the first lens 40 facing the first circularly polarized light selective reflection element 50 is flat, it is possible to easily bond the first circularly polarized light selective reflection element 50 to the first lens 40, which is thought to improve productivity.

[0184] Furthermore, it is possible to impart to the display panel-side PB lens 42PB the lens power obtained when the surface of second lens 41 facing the second circularly polarized light selective reflection element 60 is spherical, thereby improving the display characteristics of display device 100 while making the surface of second lens 41 facing the second circularly polarized light selective reflection element 60 flat. Furthermore, since the surface of second lens 41 facing the second circularly polarized light selective reflection element 60 is flat, it is possible to easily bond second circularly polarized light selective reflection element 60 to second lens 41, which is thought to improve productivity.

[0185] Furthermore, as shown in FIG. 12, it becomes possible to use light on the second path RT2 in addition to the light on the first path RT1, thereby improving the light utilization efficiency.

[0186] Furthermore, in this embodiment, it is possible to prevent ghost images from being seen. Here, the light that is not diffracted by the PB lens 40PB passes through the circularly polarized light selective reflection element 50 because its polarization state is different from the intended state. However, in the display device 100 of this embodiment, by arranging the observer-side PB lens 41PB between the circularly polarized light selective reflection element 50 and the observer U, the light that passes through via the correct path is focused on the eyes of the observer U, and the light that causes the ghost image is not focused on the eyes of the observer U, which is thought to prevent the ghost image from being seen. [Explanation of symbols]

[0187] 1L: Linearly polarized light 1LB, 1LG, 1LP, 1LR, 1LW, 1LY: Light 2L, 3L: Circularly polarized light 10: Display panel (self-luminous panel) 20: Circular polarizing element 21, 80: Linear polarizer 22, 23, 52: 1 / 4 wave plate 30: Half mirror 40, 41: Lens 40A, 40B: Lens section 40PB: Pancharatnam Berry Lens (PB Lens) 41PB: Observer side PB lens 42PB: PB lens on the display panel side 50, 60: Circularly polarized selective reflection element 51: Reflective linear polarizer 70: Display panel (LCD panel) 71: Substrate (TFT substrate) 72: Substrate (opposing substrate) 73: Liquid crystal layer 74: Color filter 75: Black Matrix 74B: Blue color filter 74G: Green color filter 74R: Red color filter 100, 100R: Display device 200: Head-mounted display 210: Mounting part 220: Face cushion 410: Support substrate 420: Liquid crystal molecules 420A: Optically anisotropic layer 420X: long axis LC0, LC1, LC2: Left circular polarization R0, R1, R2: area RT1, RT2: Route U: Observer

Claims

1. A display panel; a second circularly polarized light selective reflection element; Pancharatnam Berry lens on the display panel side, A second lens, Half mirror and The first lens, a Pancharatnam Berry lens that focuses incident left-handed or right-handed circularly polarized light and diverges incident right-handed circularly polarized light; a first circularly polarized light selective reflection element, the surface of the first lens facing the first circularly polarized light selective reflection element is flat; The display device according to claim 1, wherein the surface of the second lens facing the second circularly polarized light selective reflection element is flat.

2. The display device according to claim 1 , wherein the first lens includes a first lens portion and a second lens portion.

3. A display panel; Half mirror and Lenses and a Pancharatnam Berry lens that focuses incident left-handed or right-handed circularly polarized light and diverges incident right-handed circularly polarized light; a circularly polarized light selective reflection element; an observer-side Pancharatnam Berry lens, and The display device is characterized in that the surface of the lens facing the circularly polarized light selective reflection element is flat.

4. A head-mounted display comprising: the display device according to any one of claims 1 to 3; and a mounting part to be mounted on the head of the observer.

Images