# US 12,007,594 B2 · Polarization conversion element > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,007,594 B2 - Document ID: US12007594B2 - Status: Granted - Kind: B2 - Application number: 18/465,199 - Filed: 2023-09-12 - Published: 2023-12-28 - Granted: 2024-06-11 - Earliest claimed: 2021-03-12 - Assignees: Japan Display Inc. - Applicants: Japan Display Inc. - Inventors: Junji Kobashi - Web page: https://patentgrep.com/patent/US12007594B2 ## CPC - G02B 5/3016: {involving passive liquid crystal elements (optical properties of liquid crystals G02F1/0063; polarising elements associated with active liquid crystal devices G02F1/133528)} - G02B 5/18: Diffraction gratings {(holographic optical elements G02B5/32, G03H; integrally combined with optical fibres G02B6/02057; for coupling light guides G02B6/34; integrally combined with optical integrated light guides G02B6/12; grating systems G02B27/44)} - G02B 5/1814: {structurally combined with one or more further optical elements, e.g. lenses, mirrors, prisms or other diffraction gratings (G02B5/189 takes precedence)} - G02B 5/30: Polarising elements (light-modulating devices with active elements G02F1/00) - G02F 1/1335: Structural association of cells with optical devices, e.g. polarisers or reflectors - G02F 1/133536: {Reflective polarizers (G02F1/13362 takes precedence)} - G02F 1/1336: {Illuminating devices} - G02F 1/133607: {the light controlling member including light directing or refracting elements, e.g. prisms or lenses} - G02F 1/1337: Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers - G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS - G02F: OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS ## Abstract According to one embodiment, a polarization conversion element includes a first light guide including a first main surface and a side surface, a transmissive first polarization grating opposed to the side surface, and a reflective second polarization grating opposed to the first main surface. The first polarization grating is configured to diffract first circularly polarized light of unpolarized incident light and to diffract second circularly polarized light which rotates in a direction opposite to the first circularly polarized light in a direction different from the first circularly polarized light. The second polarization grating is configured to reflect the first circularly polarized light on the reflective surface. ## Claims ### Claim 1 A polarization conversion element comprising: a first light guide including a first main surface, a second main surface on a side opposite to the first main surface, and a side surface; a transmissive first polarization grating opposed to the side surface; and a reflective second polarization grating opposed to the first main surface, wherein the first polarization grating contains nematic liquid crystal aligned along a normal direction of the side surface, and is configured to diffract first circularly polarized light of unpolarized incident light and to diffract second circularly polarized light which rotates in a direction opposite to the first circularly polarized light in a direction different from the first circularly polarized light, and the second polarization grating contains cholesteric liquid crystal forming a reflective surface inclined to the first main surface, and is configured to reflect the first circularly polarized light on the reflective surface. ### Claim 2 (depends on 1) The polarization conversion element of claim 1, further comprising: a retardation film opposed to the second main surface. ### Claim 3 (depends on 2) The polarization conversion element of claim 2, wherein the second polarization grating includes a first area containing first cholesteric liquid crystal and a second area containing second cholesteric liquid crystal, the first area is located between the first polarization grating and the second area, each of the first cholesteric liquid crystal and the second cholesteric liquid crystal has a same helical pitch, and a thickness of the first area is smaller than a thickness of the second area. ### Claim 4 (depends on 2) The polarization conversion element of claim 2, wherein the second polarization grating has a lens action of converging and diverging the first circularly polarized light. ### Claim 5 (depends on 1) The polarization conversion element of claim 1, wherein the second polarization grating includes a first area containing first cholesteric liquid crystal and a second area containing second cholesteric liquid crystal, the first area is located between the first polarization grating and the second area, each of the first cholesteric liquid crystal and the second cholesteric liquid crystal has a same helical pitch, and a thickness of the first area is smaller than a thickness of the second area. ### Claim 6 (depends on 1) The polarization conversion element of claim 1, wherein the second polarization grating has a lens action of converging and diverging the first circularly polarized light. ### Claim 7 (depends on 1) The polarization conversion element of claim 1, further comprising: a reflective third polarization grating opposed to the second polarization grating, wherein the third polarization grating contains cholesteric liquid crystal forming a reflective surface inclined to the first main surface, and a helical pitch of the cholesteric liquid crystal in the third polarization grating is different from a helical pitch of the cholesteric liquid crystal in the second polarization grating. ### Claim 8 (depends on 7) The polarization conversion element of claim 7, wherein an inclination angle of the reflective surface in the third polarization grating is different from an inclination angle of the reflective surface in the second polarization grating. ### Claim 9 (depends on 1) The polarization conversion element of claim 1, further comprising: a reflective third polarization grating opposed to the second main surface; and a second light guide opposed to the third polarization grating, wherein the third polarization grating contains cholesteric liquid crystal forming a reflective surface inclined to the first main surface, and a helical pitch of the cholesteric liquid crystal in the third polarization grating is different from a helical pitch of the cholesteric liquid crystal in the second polarization grating. ### Claim 10 (depends on 9) The polarization conversion element of claim 9, wherein an inclination angle of the reflective surface in the third polarization grating is different from an inclination angle of the reflective surface in the second polarization grating. ### Claim 11 A polarization conversion element comprising: a first light guide including a first main surface, a second main surface on a side opposite to the first main surface, and a side surface; a transmissive first polarization grating opposed to the side surface; and a transmissive second polarization grating opposed to the second main surface, wherein the first polarization grating contains nematic liquid crystal aligned along a normal direction of the side surface, and is configured to diffract first circularly polarized light of unpolarized incident light and to diffract second circularly polarized light which rotates in a direction opposite to the first circularly polarized light in a direction different from the first circularly polarized light, and the second polarization grating contains nematic liquid crystal aligned along a normal of the second main surface, and is configured to diffract the first circularly polarized light and the second circularly polarized light. ### Claim 12 (depends on 11) The polarization conversion element of claim 11, further comprising: a retardation film opposed to the second polarization grating.