Grating-assisted field of view expansion

Abstract

A field of view of an imaging or ranging device may be increased multiple times by providing a switchable diffraction grating structure upstream of an imaging camera or ranging light source. The switchable diffraction grating changes the angle of propagating of incoming light by a fixed step, enabling the device to switch between several portions of a compound field of view. The switchable diffraction grating structure may be supported by a lightguide that guides the image light or ranging light by a series of reflections from opposed surfaces of the lightguide.

What is claimed is: 
     
         1 . An imaging device comprising:
 a camera for capturing an image within a camera field of view; and   a diffraction grating structure upstream of the camera, the diffraction grating structure having a switchable grating period for switching the camera field of view between a plurality of overlapping portions of a compound field of view, whereby the compound field of view is greater than the camera field of view.   
     
     
         2 . The imaging device of  claim 1 , further comprising:
 a lightguide for propagating a light beam therein by a series of internal reflections, the light beam carrying the image; and   an in-coupling grating supported by the lightguide for in-coupling the light beam into the lightguide;   wherein the diffraction grating structure is supported by the lightguide for out-coupling, towards the camera, portions of the light beam propagating in the lightguide.   
     
     
         3 . The imaging device of  claim 1 , further comprising:
 a lightguide for propagating a light beam therein by a series of internal reflections, the light beam carrying the image; and   an out-coupling grating supported by the lightguide for out-coupling portions of the light beam propagating in the lightguide towards the camera;   wherein the diffraction grating structure is supported by the lightguide for in-coupling the light beam into the lightguide.   
     
     
         4 . The imaging device of  claim 1 , wherein: the camera comprises a color camera for a near-eye display; and
 the image comprises a color image of outside environment of the near-eye display.   
     
     
         5 . The imaging device of  claim 1 , wherein:
 the camera comprises a depth sensing camera for a near-eye display; and   the image comprises depth information associated with pixels of the image.   
     
     
         6 . The imaging device of  claim 1 , wherein:
 the camera comprises an eye tracking camera for a near-eye display; and   the image comprises an image of an eye of a user of the near-eye display.   
     
     
         7 . The imaging device of  claim 1 , wherein the diffraction grating structure comprises a stack of switchable gratings of differing grating pitch, each switchable grating being switchable between a high-efficiency state wherein efficiency of the switchable grating is above a first threshold, and a low-efficiency state wherein the efficiency of the switchable grating is below a second threshold, wherein the second threshold is lower than the first threshold. 
     
     
         8 . The imaging device of  claim 1 , wherein the diffraction grating structure comprises a switchable polarization volume hologram (PVH) grating. 
     
     
         9 . The imaging device of  claim 1 , wherein the diffraction grating structure comprises a switchable Pancharatnam-Berry phase (PBP) liquid crystal (LC) grating. 
     
     
         10 . The imaging device of  claim 1 , wherein the diffraction grating structure comprises a switchable surface relief liquid crystal (LC) grating. 
     
     
         11 . The imaging device of  claim 1 , wherein the diffraction grating structure comprises a switchable fluidic grating. 
     
     
         12 . The imaging device of  claim 1 , further comprising an acoustic actuator coupled to a slab of transparent material, wherein the diffraction grating structure is formed by an acoustic wave generated by the acoustic actuator in the slab. 
     
     
         13 . The imaging device of  claim 1 , further comprising a controller operably coupled to the camera and the diffraction grating structure and configured to:
 operate the diffraction grating structure to switch the camera field of view between the plurality of overlapping portions of the compound field of view;   capture an image at each portion of the plurality of overlapping portions of the compound field of view; and   stitch the images captured at each portion of the plurality of overlapping portions to obtain a compound image corresponding to the compound field of view.   
     
     
         14 . An imaging method comprising:
 switching a field of view of a camera between the plurality of overlapping portions of a compound field of view by switching a grating period of a diffraction grating structure upstream of the camera;   at each portion of the plurality of overlapping portions of the compound field of view, capturing an image; and   stitching the images captured at each portion of the plurality of overlapping portions to obtain a compound image corresponding to the compound field of view.   
     
     
         15 . The imaging method of  claim 14 , wherein the switching comprises switching at least one of a stack of switchable gratings of differing grating pitch to a high-efficiency state above a first threshold, while the remaining switchable gratings of the stack are in a low-efficiency state below a second threshold lower than the first threshold. 
     
     
         16 . The imaging method of  claim 14 , wherein the switching comprises switching at least one of: a switchable polarization volume hologram (PVH) grating; a switchable Pancharatnam-Berry phase (PBP) liquid crystal (LC) grating; a switchable surface relief liquid crystal (LC) grating; or a fluidic grating. 
     
     
         17 . A ranging device comprising:
 a transmitter for providing a ranging light beam within a ranging field of view; and   a diffraction grating structure downstream of the transmitter, the diffraction grating structure having a switchable grating period for switching the ranging field of view between a plurality of overlapping portions of a compound field of view, whereby the compound field of view is greater than the ranging field of view.   
     
     
         18 . The ranging device of  claim 17 , further comprising:
 a lightguide for propagating the light beam therein by a series of internal reflections; and   an in-coupling grating supported by the lightguide for in-coupling the light beam into the lightguide;   wherein the diffraction grating structure is supported by the lightguide for out-coupling portions of the light beam propagating in the lightguide.   
     
     
         19 . The ranging device of  claim 17 , wherein the diffraction grating structure comprises a stack of switchable gratings of differing grating pitch, each switchable grating being switchable between a high-efficiency state wherein efficiency of the switchable grating is above a first threshold, and a low-efficiency state wherein the efficiency of the switchable grating is below a second threshold, wherein the second threshold is lower than the first threshold. 
     
     
         20 . The ranging device of  claim 17 , wherein the diffraction grating structure comprises at least one of: a switchable polarization volume hologram (PVH) grating; a switchable Pancharatnam-Berry phase (PBP) liquid crystal (LC) grating; a switchable surface relief liquid crystal (LC) grating; or a fluidic grating.