Adjustable focal length illuminator for a display panel

Abstract

An illuminator for a display panel includes a slab of transparent material for propagating illuminating light between outer surfaces of the slab, an out-coupler supported by the slab for out-coupling portions of the illuminating light along one of the outer surfaces of the slab, and a tunable microlens array for forming an array of light spots from the out-coupled illuminating light portions downstream of the focusing element for illuminating pixels of the display panel. The array of light spots may be repeated at a distance from the tunable microlens array due to Talbot effect. The display panel may be illuminated in a color-sequential manner, and the tunable microlens array may be used to adjust the focal plane position for each color channel individually.

What is claimed is: 
     
         1 . An illuminator comprising:
 a slab of transparent material, the slab comprising opposed first and second surfaces for propagating illuminating light in the slab by a series of internal reflections from the first and second surfaces;   an out-coupler supported by the slab for out-coupling portions of the illuminating light from the slab at the first surface; and   a tunable microlens array coupled to the first surface for forming an array of light spots from the out-coupled illuminating light portions at an adjustable distance from the first surface.   
     
     
         2 . The illuminator of  claim 1 , further comprising:
 a multi-color light source for providing the illuminating light of a color channel of a plurality of color channels; and   an in-coupler for in-coupling the illuminating light into the slab, wherein the in-coupler is configured to in-couple different color channels of the plurality of color channels at different angles, whereby a lateral position of light spots of the array of light spots depends on the color channel of the illuminating light.   
     
     
         3 . The illuminator of  claim 1 , wherein the tunable microlens array comprises a liquid crystal layer with a variable liquid crystal orientation. 
     
     
         4 . The illuminator of  claim 1 , wherein the tunable microlens array comprises a tunable liquid crystal microlens array. 
     
     
         5 . The illuminator of  claim 1 , wherein the tunable microlens array comprises an array of switchable Pancharatnam-Berry phase microlenses. 
     
     
         6 . A display apparatus comprising:
 a display panel comprising a pixel array on a substrate; and   an illuminator coupled to the display panel for illuminating the pixel array through the substrate, the illuminator comprising:
 a slab of transparent material, the slab comprising opposed first and second surfaces for propagating illuminating light in the slab by a series of internal reflections from the first and second surfaces; 
 an out-coupler supported by the slab for out-coupling portions of the illuminating light from the slab at the first surface; and 
 a tunable microlens array coupled to the first surface for forming an array of light spots from the out-coupled illuminating light portions at a distance from the first surface. 
   
     
     
         7 . The display apparatus of  claim 6 , wherein in operation, the an array of light spots is formed on the pixel array. 
     
     
         8 . The display apparatus of  claim 6 , wherein in operation, light of the array of light spots propagates through the substrate and produces an array of optical power density peaks at the pixel array due to Talbot effect. 
     
     
         9 . The display apparatus of  claim 6 , wherein the pixel array comprises a plurality of interleaved color sub-pixel arrays, each color sub-pixel array corresponding to a color channel of a plurality of color channels of an image to be displayed by the display apparatus, the illuminator further comprising:
 a multi-color light source for providing the illuminating light of a color channel of the plurality of color channels; and   an in-coupler for in-coupling the illuminating light into the slab, wherein the in-coupler is configured to in-couple different color channels of the plurality of color channels at different angles, whereby a lateral position of light spots of the array of light spots depends on the color channel of the illuminating light.   
     
     
         10 . The display apparatus of  claim 9 , wherein in operation, light of the array of light spots propagates through the substrate and produces an array of optical power density peaks at the pixel array due to Talbot effect, wherein a lateral position of optical power density peaks of the array of optical power density peaks is matched to a lateral position of a corresponding color sub-pixel sub-array of the plurality of interleaved color sub-pixel arrays. 
     
     
         11 . The display apparatus of  claim 9 , further comprising a controller operably coupled to the multi-color light source and the tunable microlens array and configured to:
 operate the multi-color light source to provide the illuminating light in a color-sequential manner; and   tune the tunable microlens array to adjust the distance depending on a current color channel of the illuminating light.   
     
     
         12 . The display apparatus of  claim 9 , wherein the in-coupler comprises a tiltable reflector for varying an angle of incidence of the illuminating light onto the slab. 
     
     
         13 . The display apparatus of  claim 6 , wherein the tunable microlens array comprises a liquid crystal layer with a variable liquid crystal orientation. 
     
     
         14 . The display apparatus of  claim 6 , wherein the tunable microlens array comprises a tunable liquid crystal microlens array. 
     
     
         15 . The display apparatus of  claim 6 , wherein the tunable microlens array comprises an array of switchable Pancharatnam-Berry phase microlenses. 
     
     
         16 . A method for illuminating a display panel comprising a pixel array on a substrate, the method comprising:
 propagating illuminating light in a slab of transparent material by a series of internal reflections from opposed first and second surfaces of the slab;   out-coupling portions of the illuminating light from the slab at the first surface using an out-coupler;   focusing the out-coupled illuminating light portions at a distance from the first surface using a tunable microlens array; and   tuning the tunable microlens array to form an array of light spots for illuminating the pixel array of the display panel.   
     
     
         17 . The method of  claim 16 , further comprising propagating light of the array of light spots through the substrate to produce an array of optical power density peaks at the pixel array due to Talbot effect. 
     
     
         18 . The method of  claim 16 , further comprising:
 operating a multi-color light source to provide the illuminating light in a color-sequential manner; and   tuning the tunable microlens array to adjust the distance depending on a current color of the illuminating light.   
     
     
         19 . The method of  claim 18 , further comprising in-coupling different color channels of the plurality of color channels at different angles, whereby a lateral position of light spots of the array of light spots depends on a color channel of the illuminating light. 
     
     
         20 . The method of  claim 19 , wherein the pixel array comprises a plurality of interleaved color sub-pixel arrays, the method further comprising:
 propagating light of the array of light spots through the substrate to produce an array of optical power density peaks at the pixel array due to Talbot effect; and   matching a lateral position of the optical power density peaks of the array of optical power density peaks to a lateral position of a corresponding color sub-pixel sub-array of the plurality of interleaved color sub-pixel arrays.