# US 2018/0324402 A1 · Resonating optical waveguide using multiple diffractive optical elements > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2018/0324402 A1 - Document ID: US20180324402A1 - Status: Published application - Kind: A1 - Application number: 15/589,478 - Filed: 2017-05-08 - Published: 2018-11-08 - Earliest claimed: 2017-05-08 - Assignees: Microsoft Technology Licensing, LLC - Applicants: Microsoft Technology Licensing, LLC - Inventors: Joseph Daniel LOWNEY; Richard Andrew WALL - Web page: https://patentgrep.com/patent/US20180324402A1 ## CPC - H04N 13/344: with head-mounted left-right displays - G02B 6/00: Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings - G02B 27/0172: {characterised by optical features} - H04N 13/383: for tracking with gaze detection, i.e. detecting the lines of sight of the viewer's eyes - G02B 2027/0118: {comprising devices for improving the contrast of the display / brillance control visibility} - G02B 2027/0178: {Eyeglass type (eyeglass details G02C)} - H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION - G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS ## Abstract A resonating optical waveguide that increases image intensity and uniformity is provided. The waveguide includes a first diffractive optical element that allows light from an exit pupil of a projector to enter the waveguide and travel in a first direction, and a second diffractive optical element that directs some of the entered light to exit the waveguide to form an expanded pupil. Rather than allow the remaining, non-directed, light to exit at an edge of the waveguide, the optical waveguide further includes a third diffractive optical element that redirects some the remaining light back through the second diffractive optical element in a second direction where it may exit the waveguide as part of the expanded pupil. An additional fourth diffractive optical element may be included to further redirect the light through the second diffractive optical element again. ## Claims ### Claim 1 A resonating optical waveguide comprising: a first end; a second end; a first diffractive optical element configured to: allow light to enter into the resonating optical waveguide; and cause the light to traverse in a first direction towards the first end; a second diffractive optical element configured to: receive the light traversing in the first direction from the first diffractive optical element; and allow a first portion of the light traversing in the first direction to exit out of the resonating optical waveguide; and a third diffractive optical element configured to: receive a second portion of the light traversing in the first direction from the second diffractive optical element; and cause a third portion of the light to traverse in a second direction towards the second end, wherein the second diffractive optical element is further configured to: receive the third portion of the light traversing in the second direction from the third diffractive optical element; and allow a fourth portion of the light traversing in the second direction to exit out of the resonating optical waveguide. ### Claim 2 (depends on 1) The resonating optical waveguide of claim 1, further comprising a fourth diffractive optical element configured to: receive a fifth portion of the light traversing in the second direction from the second diffractive optical element; and cause a sixth portion of the light to traverse in the first direction towards the first end. ### Claim 3 (depends on 1) The resonating optical waveguide of claim 1, wherein the resonating optical waveguide further comprises a front surface and a rear surface. ### Claim 4 (depends on 3) The resonating optical waveguide of claim 3, wherein the second diffractive optical element configured to allow the first portion of the light traversing in the first direction to exit out of the resonating optical waveguide comprises the second diffractive optical element configured to allow the first portion of the light traversing in the first direction to exit out of the resonating optical waveguide through the rear surface. ### Claim 5 (depends on 3) The resonating optical waveguide of claim 3, wherein the first diffractive optical element comprises a coating on one of the front surface or the rear surface. ### Claim 6 (depends on 5) The resonating optical waveguide of claim 5, wherein the coating is a surface-relief diffraction grating or a volume holographic grating. ### Claim 7 (depends on 1) The resonating optical waveguide of claim 1, wherein the first direction and the second direction are opposite directions. ### Claim 8 (depends on 1) The resonating optical waveguide of claim 1, wherein the first diffractive optical element, the second diffractive optical element, and the third diffractive optical element each have a grating vector, and the grating vector associated with the third diffractive optical element has a value that is twice a value of the grating vector associated with the first diffractive optical element and a value of the grating vector associated with the second diffractive optical element. ### Claim 9 A head mounted display device comprising: a projector; a controller coupled to the projector and configured to cause the projector to project light comprising a display image; and a plurality of resonating optical waveguides, wherein each resonating optical waveguide comprises: a first end; a second end; a first diffractive optical element configured to: allow the light to enter into the resonating optical waveguide; and cause the light to traverse in a first direction towards the first end; a second diffractive optical element configured to: receive the light traversing in the first direction from the first diffractive optical element; and allow a first portion of the light traversing in the first direction to exit out of the resonating optical waveguide; and a third diffractive optical element configured to: receive a second portion of the light traversing in the first direction from the second diffractive optical element; and cause a third portion of the light to traverse in a second direction towards the second end, wherein the second diffractive optical element is further configured to: receive the third portion of the light traversing in the second direction from the third diffractive optical element; and allow a fourth portion of the light traversing in the second direction to exit out of the resonating optical waveguide. ### Claim 10 (depends on 9) The head mounted display device of claim 9, wherein each resonating optical waveguide further comprises a fourth diffractive optical element configured to: receive a fifth portion of the light traversing in the second direction from the second diffractive optical element; and cause a sixth portion of the light to traverse in the first direction towards the first end. ### Claim 11 (depends on 9) The head mounted display device of claim 9, wherein each resonating optical waveguide further comprises a front surface and a rear surface. ### Claim 12 (depends on 9) The head mounted display device of claim 9, wherein the second diffractive optical element of each resonating optical waveguide configured to allow the first portion of the light traversing in the first direction to exit out of the resonating optical waveguide comprises the second diffractive optical element of each optical waveguide configured to allow the first portion of the light traversing in the first direction to exit out of the resonating optical waveguide through the rear surface. ### Claim 13 (depends on 9) The head mounted display device of claim 9, wherein the first diffractive optical element of each resonating optical waveguide comprises a coating on one of the front surface or the rear surface. ### Claim 14 (depends on 13) The head mounted display device of claim 13, wherein the coating is a surface-relief diffraction grating or a volume holographic grating. ### Claim 15 (depends on 9) The head mounted display device of claim 9, wherein the first diffractive optical element, the second diffractive optical element, and the third diffractive optical element each have a grating vector, and the grating vector associated with the third diffractive optical element has a value that is twice a value of the grating vector associated with the first diffractive optical element and a value of the grating vector associated with the second diffractive optical element. ### Claim 16 A resonating optical waveguide comprising: a front surface and a rear surface; a first coating on the front surface that allows light to enter the resonating optical waveguide and traverse in a first direction within the resonating optical waveguide; a second coating on the front surface that receives the light traversing in the first direction, causes a first portion of the light to exit the resonating optical waveguide through the rear surface, and allows a second portion of the light to continue to traverse in the first direction; and a third coating on the front surface that receives the second portion of the light traversing in the first direction, and causes a third portion of the light to traverse in a second direction within the resonating optical waveguide. ### Claim 17 (depends on 16) The resonating optical waveguide of claim 16, wherein the first direction and the second direction are opposite directions. ### Claim 18 (depends on 16) The resonating optical waveguide of claim 16, wherein the second coating further receives the third portion of the light, and allows a fourth portion of the light to exit the resonating optical waveguide through the rear surface. ### Claim 19 (depends on 16) The resonating optical waveguide of claim 16, wherein the first coating and the third coating are surface-relief diffraction gratings or volume holographic gratings. ### Claim 20 (depends on 16) The resonating optical waveguide of claim 16, wherein the third coating has a grating vector that has a value that is twice a value of a grating vector of the first coating.