# US 10,481,687 B1 · Waveguide integrated eye tracking > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,481,687 B1 - Document ID: US10481687B1 - Status: Granted - Kind: B1 - Application number: 16/279,784 - Filed: 2019-02-19 - Granted: 2019-11-19 - Earliest claimed: 2016-09-02 - Assignees: Facebook Technologies, LLC - Applicants: Facebook Technologies, LLC - Inventors: Nicholas Daniel Trail - Web page: https://patentgrep.com/patent/US10481687B1 ## CPC - G06F 3/013: {Eye tracking input arrangements (G06F3/015 takes precedence)} - G02B 6/0035: {provided on the surface of the light guide or in the bulk of it} - G02B 27/0081: {with means for altering, e.g. enlarging, the entrance or exit pupil} - G02B 27/0093: {with means for monitoring data relating to the user, e.g. head-tracking, eye-tracking} - G02B 27/0172: {characterised by optical features} - G02F 1/292: {by controlled diffraction or phased-array beam steering (controlled diffraction for optical switching G02F1/31)} - G06F 1/163: {Wearable computers, e.g. on a belt} - G06F 3/011: {Arrangements for interaction with the human body, e.g. for user immersion in virtual reality (blind teaching G09B21/00)} - H04N 23/56: provided with illuminating means - G02B 2027/0147: {comprising a device modifying the resolution of the displayed image} - G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N) - 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 - H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION ## Abstract An eye tracker for determining a position of an eye, which may be integrated into a head-mounted display. The eye tracker includes a waveguide, switchable Bragg gratings (SBGs) that selectively out couple light from the waveguide, light sources coupled to the waveguide, a detector coupled to a return path of the waveguide, and a controller. The controller instructs at least one light source to emit at least one light beam propagating through the waveguide, and activates at least one SBG to out-couple the at least one light beam from the waveguide toward the eye. The waveguide in-couples at least one reflected light signal reflected from the eye that originates from the at least one light beam out-coupled from the waveguide. The detector detects the at least one reflected light signal. The controller determines a position of the eye using the detected at least one reflected light signal. ## Claims ### Claim 1 An eye tracker comprising: a waveguide; a plurality of switchable gratings configured to selectively out-couple light from the waveguide, each switchable grating being designed for a specific out-coupling angle; an array of light sources coupled to the waveguide; and a controller configured to: instruct multiple light sources in the array to emit light beams for propagation through the waveguide, activate two or more of the switchable gratings to out-couple the light beams from a subset of different emission portions of the waveguide toward an eye, each light beam out-coupled at a corresponding out-coupling angle of a corresponding emission portion from the subset of different emission portions, wherein activation of a unique pair of a light source in the array and a switchable grating of the two or more switchable gratings maps to a unique emission portion of the waveguide for out-coupling, and determine a position of the eye using light reflected from at least one surface of the eye that originate from the light beams out-coupled from the different emission portions of the waveguide. ### Claim 2 (depends on 1) The eye tracker of claim 1, wherein the controller is further configured to: calculate position data based on the reflected light in-coupled by the waveguide; compare the calculated position data with calibrated data that corresponds to an out-coupling location on the waveguide toward which the eye is looking directly; and determine the position of the eye based on the comparison. ### Claim 3 (depends on 2) The eye tracker of claim 2, wherein the controller is configured to calculate the position data by calculating magnitudes of light signals detected from the reflected light in-coupled by the waveguide. ### Claim 4 (depends on 2) The eye tracker of claim 2, wherein the controller is configured to calculate the position data by calculating relative contrasts of light signals detected from the reflected light in-coupled by the waveguide. ### Claim 5 (depends on 2) The eye tracker of claim 2, wherein the controller is further configured to: instruct at least one other light source of the array of light sources to emit light, when the calculated position data do not match the calibrated data; activate at least one other switchable grating of the plurality of switchable gratings to out-couple the emitted light; calculate other position data based on one or more light beams reflected from one or more surfaces of the eye and in-coupled by the waveguide; compare the other position data with the calibrated data; and update the position of the eye based on the comparison between the other position data and the calibrated data. ### Claim 6 (depends on 1) The eye tracker of claim 1, wherein each light beam emitted from a different light source of the array of light sources is out-coupled from the waveguide at a different angle relative to an out-coupling location on one of the activated switchable gratings and illuminates a different spatial region of the eye. ### Claim 7 (depends on 1) The eye tracker of claim 1, further comprising: a detector configured to detect light signals by capturing the reflected light coupled into the waveguide and propagated through multiple return paths of the waveguide toward the detector. ### Claim 8 (depends on 7) The eye tracker of claim 7, wherein the detector is coupled through a beam-splitter to the array of light sources. ### Claim 9 (depends on 1) The eye tracker of claim 1, wherein the controller is further configured to determine calibrated data for a user during a startup process. ### Claim 10 (depends on 1) The eye tracker of claim 1, wherein the controller is further configured to: calculate position data based on the reflected light in-coupled by the waveguide; map the position data to field locations on the waveguide from which the light beams were out-coupled from the waveguide; and determine the position of the eye based on the mapping. ### Claim 11 (depends on 1) The eye tracker of claim 1, wherein the controller is further configured to: instruct, at a time instant of a plurality of time instants, a pattern of light sources in the array of light sources to emit light; activate, at the time instant, multiple switchable gratings of the plurality of switchable gratings corresponding to the pattern of light sources to out-couple the light; and update, at the time instant, the position of the eye using light signals reflected from one or more surfaces of the eye that originate from the pattern of light sources. ### Claim 12 A method comprising: instructing multiple light sources in an array of light sources to emit light beams for propagation through a waveguide coupled to the array of light sources and to a plurality of gratings, each switchable grating being designed for a specific out-coupling angle; activating two or more switchable gratings of the plurality of switchable gratings to out-couple the light beams from a subset of different emission portions of the waveguide toward an eye, each light beam out-coupled at a corresponding out-coupling angle of a corresponding emission portion from the subset of different emission portions, wherein activation of a unique pair of a light source in the array and a switchable grating of the two or more switchable gratings maps to a unique emission portion of the waveguide for out-coupling; and determining a position of the eye using light reflected from at least one surface of the eye that originate from the light beams out-coupled from the different emission portions of the waveguide. ### Claim 13 (depends on 12) The method of claim 12, further comprising: calculating position data based on the reflected light in-coupled by the waveguide; comparing the calculated position data with calibrated data that corresponds to an out-coupling location on the waveguide toward which the eye is looking directly; and determining the position of the eye based on the comparison. ### Claim 14 (depends on 13) The method of claim 13, further comprising calculating the position data by calculating magnitudes of light signals detected from the reflected light in-coupled by the waveguide. ### Claim 15 (depends on 13) The method of claim 13, further comprising: instructing at least one other light source of the array of light sources to emit light, when the calculated position data do not match the calibrated data; activating at least one other switchable grating of the plurality of switchable gratings to out-couple the emitted light; calculating other position data based on one or more light beams reflected from one or more surfaces of the eye and in-coupled by the waveguide; comparing the other position data with the calibrated data; and updating the position of the eye based on the comparison between the other position data and the calibrated data. ### Claim 16 (depends on 12) The method of claim 12, wherein each light beam emitted from a different light source of the array of light sources is out-coupled from the waveguide at a different angle relative to an out-coupling location on one of the activated switchable gratings and illuminates a different spatial region of the eye. ### Claim 17 (depends on 12) The method of claim 12, further comprising: detecting, by a detector, light signals by capturing the reflected light coupled into the waveguide and propagated through multiple return paths of the waveguide toward the detector. ### Claim 18 (depends on 12) The method of claim 12, further comprising: instructing, at a time instant of a plurality of time instants, a pattern of light sources in the array of light sources to emit light; activating, at the time instant, multiple switchable gratings of the plurality of switchable gratings corresponding to the pattern of light sources to out-couple the light toward the eye; and updating, at the time instant, the position of the eye using light signals reflected from one or more surfaces of the eye that originate from the pattern of light sources. ### Claim 19 A head-mounted display (HMD) comprising: a display configured to emit image light; a plurality of switchable gratings configured to selectively out couple light from the waveguide, each switchable grating being designed for a specific out-coupling angle; an array of light sources coupled to the waveguide; and a controller configured to: instruct multiple light sources in the array to emit light beams for propagation through the waveguide, activate two or more of the switchable gratings to out-couple the light beams from a subset of different emission portions of the waveguide toward an eye, each light beam out-coupled at a corresponding out-coupling angle of a corresponding emission portion from the subset of different emission portions, wherein activation of a unique pair of a light source in the array and a switchable grating of the two or more switchable gratings maps to a unique emission portion of the waveguide for out-coupling, and determine a position of the eye using light reflected from at least one surface of the eye that originate from the light beams out-coupled from the different emission portions of the waveguide; and an optical assembly that provides optical correction to the image light, based at least in part on the determined position of the eye. ### Claim 20 (depends on 19) The HMD of claim 19, further comprising a varifocal module configured to adjust focus of one or more images displayed on the display, based at least in part on the determined position of the eye.