Wavefront sensing from retina-reflected light

Abstract

An eye is illuminated with illumination light. A wavefront image of retina-reflected light is generated and an accommodative eye state value is determined based at least in part on the wavefront image.

What is claimed is: 
     
         1 . A head mounted display (HMD) comprising:
 a wavefront sensor;   an illumination layer configured to illuminate an eyebox area with illumination light; and   an optical element configured to receive retina-reflected light and redirect the retina-reflected light to the wavefront sensor, wherein the retina-reflected light is the illumination light reflected by a retina of an eye.   
     
     
         2 . The HMD of  claim 1 , wherein the illumination layer includes an array of infrared in-field illuminators configured to be disposed between 10 mm and 35 mm from the eye when a user of the HMD is utilizing the HMD. 
     
     
         3 . The HMD of  claim 2 , wherein an individual infrared in-field illuminator has a footprint of less than 200 microns×200 microns. 
     
     
         4 . A near-eye optical system comprising:
 a wavefront sensor;   an array of illuminators configured to illuminate an eyebox area with illumination light; and   a combiner optical element configured to receive retina-reflected light and redirect the retina-reflected light to the wavefront sensor, wherein the retina-reflected light is the illumination light reflected by a retina.   
     
     
         5 . The near-eye optical system of  claim 4 , wherein each of the illuminators in the array includes:
 a light source emitting the illumination light; and   a beam-forming element configured to direct the illumination light toward a center of rotation of the eye.   
     
     
         6 . The near-eye optical system of  claim 5 , wherein the beam-forming elements of the light sources are configured to increase an illumination angle of the illumination light as a distance of a particular beam-forming element increases from a middle region of the array of illuminators. 
     
     
         7 . The near-eye optical system of  claim 4 , wherein the illuminators include at least one of a micro light emitting diode (micro-LED), an edge emitting LED, a vertical cavity surface emitting laser (VCSEL) diode, or a Superluminescent diode (SLED). 
     
     
         8 . The near-eye optical system of  claim 4  further comprising:
 a transparent substrate, wherein the array of illuminators is disposed on the transparent substrate, and wherein the transparent substrate is positioned to pass the retina-reflected light through the transparent substrate to the combiner optical element, the combiner optical element configured to redirect the retina-reflected light back through the transparent substrate toward the wavefront sensor. 
 
     
     
         9 . The near-eye optical system of  claim 4  further comprising:
 illumination logic configured to selectively activate individual illuminators in the array of illuminators. 
 
     
     
         10 . The near-eye optical system of  claim 4 , wherein the wavefront sensor includes:
 a camera including an image sensor; and   a lenslet array disposed in an optical path between the combiner optical element and the image sensor, wherein microlenses of the lenslet array focus the retina-reflected light onto the image sensor.   
     
     
         11 . The near-eye optical system of  claim 10 , wherein the lenslet array is positioned at a plane that is conjugate to a pupil plane of an eye. 
     
     
         12 . The near-eye optical system of  claim 10 , wherein the camera includes an infrared filter configured to pass the illumination light and reject other light wavelengths. 
     
     
         13 . The near-eye optical system of  claim 4 , wherein the combiner optical element includes a polarization-selective volume hologram that reflects a first polarization orientation of the retina-reflected light and passes polarization orientations that are other than the first polarization orientation, and wherein the combiner optical element passes visible light. 
     
     
         14 . The near-eye optical system of  claim 4 , wherein the illuminators in the array are spaced apart so that at least a portion of the illuminators will be positioned to illuminate a retina of the eye, through a pupil of the eye, over a range of eye positions. 
     
     
         15 . A method comprising:
 illuminating an eye with illumination light;   generating a wavefront image of retina-reflected light, wherein the retina-reflected light is the illumination light reflected by a retina of the eye; and   determining an accommodative eye state value based at least in part on the wavefront image.   
     
     
         16 . The method of  claim 15 , wherein generating the wavefront image includes receiving the retina-reflected light with a wavefront sensor including an image sensor and a lenslet array. 
     
     
         17 . The method of  claim 16 , wherein the lenslet array is positioned at a plane that is conjugate to a pupil plane of the eye. 
     
     
         18 . The method of  claim 16 , wherein determining the accommodative eye state value includes analyzing a spacing of beam spots of the wavefront image generated by microlenses of the lenslet array focusing the retina-reflected light onto the image sensor. 
     
     
         19 . The method of  claim 15  further comprising:
 adjusting a virtual image presented to the eye by a head mounted display in response to the accommodative eye state value. 
 
     
     
         20 . The method of  claim 15 , wherein the illumination light is collimated or near-collimated.