Eye tracker based on retinal imaging via light-guide optical element

Abstract

An apparatus (100) for deriving a gaze direction of a human eye (150) includes a light-guide optical element (LOE) (120) having pair of parallel faces (104a), (104b) deployed in facing relation to the eye (150). A coupling-in configuration, such as a set of partially-reflective surfaces (145), is associated with LOE (120) and configured for coupling-in a proportion of light incident on face (104a) so as to propagate within the LOE. Focusing optics (106) associated with LOE (120) converts sets of parallel light rays propagating within the LOE into converging beams of captured light which are sensed by an optical sensor (125). A processing system (108) processes signals from the optical sensor (125) to derive a current gaze direction of the eye. Despite the aperture-combining effect of the LOE, retinal images can be effectively recovered as the only image information brought to focus on the optical sensor.

What is claimed is: 
     
         1 . An apparatus for deriving a gaze direction of a human eye, the apparatus comprising:
 (a) a light-guide optical element (LOE) formed from transparent material and having pair of parallel faces for guiding light by internal reflection, one of said parallel faces being deployed in facing relation to the eye;   (b) a coupling-in configuration associated with said LOE, said coupling-in configuration comprising a plurality of partially-reflective surfaces deployed within said LOE obliquely to said parallel faces coupling in a proportion of light incident on one of said parallel faces within a coupling-in region so as to propagate within said LOE;   (c) focusing optics associated with said LOE and configured for converting sets of parallel light rays propagating within said LOE into converging beams of captured light;   (d) an optical sensor deployed for sensing said captured light; and   (e) a processing system including at least one processor, said processing system being electrically associated with said optical sensor and configured so as to process signals from said optical sensor to derive a current gaze direction of the eye,   
       wherein said coupling-in configuration is configured to deflect incident light rays to generate rays propagating within said LOE, said coupling-in configuration having no optical power such that each deflected ray has a direction within the LOE defined by a direction of incidence of a corresponding incident light ray, and such that a plurality of spaced-apart parallel incident rays at different locations within said coupling-in region are combined into a single ray propagating within said LOE. 
     
     
         2 . The apparatus of  claim 1 , wherein said optical sensor comprises a four-quadrant sensor. 
     
     
         3 . The apparatus of  claim 1 , wherein said optical sensor comprises an array of pixel sensing elements, and wherein said processing system processes outputs from no more than about 10 4  pixel sensing elements. 
     
     
         4 . The apparatus of  claim 1 , further comprising an illumination arrangement deployed to illuminate the eye from the direction of said coupling-in region. 
     
     
         5 . The apparatus of  claim 4 , wherein said illumination arrangement is configured to introduce illumination into said LOE so that said illumination propagates within said LOE by reflection at said pair of parallel surfaces and is coupled out towards the eye by said coupling-in configuration. 
     
     
         6 . The apparatus of  claim 4 , further comprising an illumination light-guide element formed from transparent material and having pair of parallel faces for guiding light by internal reflection, said illumination light-guide element being deployed in overlapping relation to said LOE, wherein said illumination arrangement is configured to introduce illumination into said illumination light-guide element so that said illumination propagates within said illumination light-guide element by reflection at said pair of parallel surfaces and is coupled out towards the eye by a coupling-out configuration associated with said illumination light-guide element. 
     
     
         7 . The apparatus of  claim 4 , wherein said illumination arrangement is associated with said processing system, said processing system actuating said illumination arrangement to generate illumination pulses with a pulse duration, and wherein said processing system processes signals derived from said optical sensor corresponding to captured light incident during said pulse duration. 
     
     
         8 . The apparatus of  claim 4 , further comprising a passband spectral filter deployed to obstruct light of wavelengths outside a given range of wavelengths from reaching said optical sensor, and wherein said illumination arrangement generates illumination primarily within said given range of wavelengths. 
     
     
         9 . The apparatus of  claim 8 , wherein said given range of wavelengths is in a non-visible region of the electromagnetic radiation spectrum. 
     
     
         10 . The apparatus of  claim 4 , wherein said illumination arrangement comprises a plurality of separately controlled illumination pixels, and wherein said processing system selectively actuates said illumination pixels so as to illuminate selectively along directions corresponding to a selected region of the retina of the eye. 
     
     
         11 . The apparatus of  claim 10 , wherein during ongoing tracking of the eye gaze direction, said selected region of the retina is a region including the optic disc of the eye. 
     
     
         12 . The apparatus of  claim 1 , wherein said processing system is configured to process signals from said optical sensor to derive a center of an intensity distribution corresponding to reflection from the retina of the eye, and thereby to determine the current gaze direction of the eye. 
     
     
         13 . The apparatus of  claim 1 , wherein said processing system is configured to process signals from said optical sensor to detect a location of at least one prominent feature of the retina of the eye, and thereby to determine the current gaze direction of the eye. 
     
     
         14 . The apparatus of  claim 1 , wherein said processing system is configured to process signals from said optical sensor to track a pattern of blood vessels in the retina of the eye, and thereby to determine the current gaze direction of the eye. 
     
     
         15 . The apparatus of  claim 1 , further comprising an image projector coupled to said LOE so as to introduce a collimated image into said LOE such that said collimated image propagates via internal reflection within said LOE and is coupled out of said LOE towards the eye by said coupling-in configuration. 
     
     
         16 . The apparatus of  claim 15 , wherein said image projector is associated with said processing system, and wherein said processing system actuates said image projector to generate illumination pulses with a pulse duration, said processing system processing signals derived from said optical sensor corresponding to captured light incident during said pulse duration. 
     
     
         17 . The apparatus of  claim 16 , wherein said processing system generates said pulses so as to correspond to a selected subsection of a projected image, and such that said pulses contribute to perception of the projected image. 
     
     
         18 . The apparatus of  claim 1 , further comprising a support configuration for supporting the apparatus relative to the head of a human user such that said LOE is deployed in facing relation to a first eye of the user, the apparatus further comprising:
 (a) a second-eye light-guide optical element (LOE) formed from transparent material and having pair of parallel faces for guiding light by internal reflection, one of said parallel faces being deployed in facing relation to a second eye of the user;   (b) a coupling-in configuration associated with said second-eye LOE and configured for coupling-in a proportion of light incident on one of said parallel faces within a coupling-in region so as to propagate within said LOE;   (c) focusing optics associated with said second-eye LOE and configured for converting sets of parallel light rays propagating within said LOE into converging beams of captured light; and   (d) a second-eye optical sensor deployed for sensing said captured light,   
       wherein said processing system is further associated electrically associated with said second-eye optical sensor and configured so as to process signals from both of said optical sensors to derive a current gaze direction of the eyes of the user. 
     
     
         19 . An apparatus for deriving a gaze direction of a human eye, the apparatus comprising:
 (a) a light-guide optical element (LOE) formed from transparent material and having pair of parallel faces for guiding light by internal reflection, one of said parallel faces being deployed in facing relation to the eye;   (b) a coupling-in configuration associated with said LOE, said coupling-in configuration comprising a plurality of partially-reflective surfaces deployed within said LOE obliquely to said parallel faces coupling in a proportion of light incident on one of said parallel faces within a coupling-in region so as to propagate within said LOE by internal reflection;   (c) focusing optics associated with said LOE and configured for converting sets of parallel light rays propagating within said LOE into converging beams of captured light, said focusing optics having a focal length defining a focal plane;   (d) an optical sensor deployed at said focal plane for sensing said captured light; and   (e) a processing system including at least one processor, said processing system being electrically associated with said optical sensor and configured so as to process signals from said optical sensor to derive a current gaze direction of the eye,   
       wherein said coupling-in configuration is configured to deflect incident light rays to generate rays propagating by internal reflection within said LOE, said coupling-in configuration having no optical power such that each deflected ray has a direction within the LOE defined by a direction of incidence of a corresponding incident light ray, such that a proportion of light reflected from a retina of the eye and collimated by an ocular lens of the eye is coupled in to said LOE and focused by said focusing optics on said optical sensor while light diverging from other surfaces of the eye are defocussed at said optical sensor.