# US 10,768,348 B2 · Optical display device > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,768,348 B2 - Document ID: US10768348B2 - Status: Granted - Kind: B2 - Application number: 15/579,347 - Filed: 2016-06-01 - Published: 2018-08-02 - Granted: 2020-09-08 - Earliest claimed: 2015-06-10 - Assignees: Wave Optics Ltd. - Applicants: Wave Optics Ltd - Inventors: Salim Valera - Web page: https://patentgrep.com/patent/US10768348B2 ## CPC - 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 6/00: Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings - G02B 6/34: utilising prism or grating {(G02B6/293 takes precedence)} - G02B 27/0101: {characterised by optical features (G02B27/0172 takes precedence)} - G02B 27/0172: {characterised by optical features} - G02B 27/1086: {operating by diffraction only} - G02B 2027/0118: {comprising devices for improving the contrast of the display / brillance control visibility} - G02B 2027/0123: {comprising devices increasing the field of view} - G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS ## Abstract An optical display device (600, 700) is disclosed. A diffractive optical element (618, 718) is mounted on a substrate (611, 711). The diffractive optical element comprises a blazed grating (619, 719) and a remnant layer (617, 717) which is formed of the same polymer-based material as the blazed grating. The remnant layer (617, 717) is positioned adjacent the substrate (611, 711) and a refractive index mismatch is provided between the two. The depth of the remnant layer is selected so that light diffracted by the grating and light reflected by the interface re-combine and interfere constructively for selected angles of incidence in order to undergo thin-film interference. ## Claims ### Claim 1 An optical display device comprising: a substrate; and a diffractive optical element comprising a surface relief grating and a remnant layer, wherein the remnant layer is provided between the surface relief grating and the substrate, and the remnant layer has an absolute thickness that is less than 500 nm; wherein a partially reflective interface is provided between the substrate and the remnant layer, and wherein a thickness of the remnant layer is controlled to enable constructive thin-film interference for light having a predetermined wavelength that is received at the partially reflective interface from the substrate at a predetermined angle of incidence. ### Claim 2 (depends on 1) The optical display device of claim 1 wherein the partially reflective interface is provided between the substrate and the diffractive optical element, and the substrate and the diffractive optical element have respective refractive indices that are mismatched. ### Claim 3 (depends on 2) The optical display device of any of claim 2 wherein the refractive index of the substrate is less than the refractive index of the diffractive optical element. ### Claim 4 (depends on 1) The optical display device of claim 1 wherein the thickness of the remnant layer is controlled to enable thin-film interference for light in a range of wavelengths from a first wavelength to a second wavelength, and wherein an optical thickness of the remnant layer is approximately half of the average of the first and second wavelengths. ### Claim 5 (depends on 1) The optical display device of claim 1 wherein the diffractive optical element is an input diffractive optical element, configured to couple light into the substrate for total internal reflection. ### Claim 6 (depends on 5) The optical display device of claim 5 wherein a reflective coating is provided to the diffractive optical element to improve the efficiency with which light is coupled into the substrate. ### Claim 7 (depends on 5) The optical display device of claim 5 further comprising an output diffractive optical element comprising an output surface relief grating and an output remnant layer, wherein the output remnant layer is provided between the output surface relief grating and the substrate, and wherein an output partially reflective interface is provided between the substrate and the output remnant layer, and wherein a thickness of the output remnant layer is controlled to enable thin-film interference for light having a predetermined wavelength that is received at the output partially reflective interface from the substrate at a predetermined angle of incidence. ### Claim 8 (depends on 1) The optical display device of claim 1 wherein the diffractive optical element is an output diffractive optical element, configured to couple light out of the substrate for viewing by a user. ### Claim 9 A method of manufacture for an optical display device, the method comprising: providing a substrate; providing a diffractive optical element comprising a surface relief grating and a remnant layer, wherein the remnant layer is provided between the surface relief grating and the substrate, and the remnant layer has an absolute thickness that is less than 500 nm; providing a partially reflective interface between the substrate and the remnant layer; and controlling a thickness of the remnant layer to enable constructive thin-film interference for light having a predetermined wavelength that is received at the partially reflective interface from the substrate at a predetermined angle of incidence. ### Claim 10 (depends on 9) The method of claim 9 wherein a mould is provided to position the diffractive optical element on the substrate. ### Claim 11 (depends on 10) The method of claim 10 wherein the mould comprises a first portion for creating the surface relief grating and a second portion for creating the remnant layer. ### Claim 12 (depends on 10) The method of claim 10 wherein the mould comprises at least one spacer for positioning the surface relief grating relative to the substrate and for controlling a depth of the remnant layer. ### Claim 13 (depends on 9) The method of claim 9 wherein providing a partially reflective interface comprises providing the substrate and the diffractive optical element with respective refractive indices that are mismatched.