# US 2018/0024286 A1 · Head-mounted display with off-board illumination > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2018/0024286 A1 - Document ID: US20180024286A1 - Status: Published application - Kind: A1 - Application number: 15/656,589 - Filed: 2017-07-21 - Published: 2018-01-25 - Earliest claimed: 2016-07-21 - Assignees: Google Inc. - Applicants: Google Inc. - Inventors: Martin Friedrich SCHUBERT; Michael GRUNDMANN - Web page: https://patentgrep.com/patent/US20180024286A1 ## CPC - G02B 6/0028: {Light guide, e.g. taper} - G02B 6/0006: {Coupling light into the fibre (in general G02B6/4298)} - G02B 6/0008: {the light being emitted at the end of the fibre} - G02B 6/005: {provided by one optical element, or plurality thereof, placed on the light output side of the light guide} - G02B 6/0068: {Arrangements of plural sources, e.g. multi-colour light sources} - G02B 6/0075: {Arrangements of multiple light guides (G02B6/0028 takes precedence)} - G02B 27/0172: {characterised by optical features} - G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS ## Abstract Techniques of providing illumination to a head-mounted display (HMD) involve providing off-board illumination apart from the HMD. An off-board illumination unit delivers the illumination to the HMD via optical fibers. The optical fibers are lightweight and do not restrict motion of a user. Because the power source is less restricted, the off-board illumination unit provides flexibility in the hardware used to generate the illumination. For example, the illumination unit may use red, green, and blue narrow-band diode lasers. Further, by controlling modes in the fiber and providing additional light-guiding hardware, the angles at which light strikes LCD pixels may be largely restricted to certain specified angles. Restricted angles of incidence enable the use of fast-switching liquid crystals without degrading the image quality. Such a restriction allows for high-resolution imaging using rapid switching of the liquid crystal which enables very low latencies. ## Claims ### Claim 1 A system, comprising: a head-mounted display, HMD; an external light source separate from the HMD, the external light source being configured and arranged to generate light; and at least one optical fiber disposed between the external light source and the HMD, the at least one optical fiber being configured to deliver light generated by the external light source to the HMD via a lightguide to provide illumination for the HMD. ### Claim 2 (depends on 1) The system as in claim 1, wherein the HMD includes a display that includes a set of spatial light modulators, SLMs. ### Claim 3 (depends on 2) The system as in claim 2, wherein an SLM of the set of SLMs includes a liquid crystal display, LCD. ### Claim 4 (depends on 3) The system as in claim 3, wherein the LCD includes LCD pixels, each LCD pixel including a twisted nematic liquid crystal. ### Claim 5 (depends on 2) The system as in claim 2, wherein an SLM of the set of SLMs includes a microelectromechanical system, MEMS, grating light valve. ### Claim 6 (depends on 1) The system as in claim 1, wherein the at least one optical fiber configured to deliver the light is further configured and arranged to output the light to the lightguide in a specified polarization state. ### Claim 7 (depends on 1) The system as in claim 1, wherein the light source includes a set of diode lasers. ### Claim 8 (depends on 1) The system as in claim 1, wherein the external light source includes a source of red light configured to generate red light, a source of green light configured to generate green light, and a source of blue light configured to generate blue light. ### Claim 9 (depends on 8) The system as in claim 8, wherein the external light source configured to generate the light is further configured to produce the red light, the green light, and the blue light in a sequential order. ### Claim 10 (depends on 8) The system as in claim 8, wherein each of the source of red light, the source of green light, and the source of blue light has a respective center wavelength larger than a specified reference wavelength. ### Claim 11 (depends on 8) The system as in claim 8, wherein the light guide includes an achromatic metasurface configured to direct the red light, the green light, and the blue light to substantially the same location within the HMD. ### Claim 12 (depends on 1) The system as in claim 1, wherein the lightguide directs the light delivered by the at least one optical fiber using a diffraction grating. ### Claim 13 (depends on 12) The system as in claim 12, wherein the diffraction grating is configured to scatter substantially all of the light coupled into the lightguide into a specified set of propagation angles. ### Claim 14 (depends on 1) The system as in claim 1, further comprising, for each of the at least one optical fiber, a respective optical system configured to send the light delivered by that optical fiber into a respective plurality of lightguides. ### Claim 15 (depends on 1) The system as in claim 1, wherein the external light source is included in a base unit, the base unit being configured to generate images for display on the HMD. ### Claim 16 A method, comprising: generating light by an external light source; and transmitting the generated light to a head-mounted display, HMD, separate from the external light source via at least one fiber optic, the at least one optical fiber being configured to deliver the light generated by the external light source to the HMD via a lightguide to provide illumination for the HMD. ### Claim 17 (depends on 16) The method as in claim 16, wherein transmitting the generated light to the HMD includes outputting the light to the lightguide in a specified polarization state. ### Claim 18 (depends on 16) The method as in claim 16, further comprising directing the light delivered by the at least one optical fiber using a diffraction grating.