Contact image sensor using switchable bragg gratings

Abstract

A contact image sensor having: an illumination; a first SBG array device; a transmission grating; a second SBG array device; a waveguiding layer having a multiplicity of waveguide cores separated by cladding material; an upper clad layer; and a platen. The sensor also including an optical device for coupling light from an illumination source into the first SBG array; and an optical coupler for coupling light out of the cores into output optical paths coupled to a detector having at least one photosensitive element.

What is claimed is: 
     
         1 . A contact image sensor comprising the following parallel optical layers configured as a stack:
 an illumination means for providing a collimated beam of first polarisation light;   a first SBG array device further comprising first and second transparent substrates sandwiching an array of selectively switchable SBG column, and transparent electrodes applied to opposing faces of said substrates and said SBG substrates together providing a first TIR light guide for transmitting light in a first TIR beam direction;   a transmission grating;   a second SBG array device further comprising third and fourth transparent substrates sandwiching a multiplicity of high index HPDLC regions separated by low index HPDLC regions and patterned transparent electrodes applied to opposing faces of said substrates; and a platen; and further comprising:   means for coupling light from said illumination means into said first TIR light guide;   means for coupling light out of said second SBG array device into an output optical path;   and a detector comprising at least one photosensitive element;   wherein said high index regions providing waveguiding cores are disposed parallel to said first beam direction,   wherein said low index HPDLC regions providing waveguide cladding, said substrate layers having a generally lower refractive index than said cores,   wherein said patterned electrodes applied to said third substrate comprise column shaped elements defining a multiplicity of selectively switchable columns of SBG elements orthogonal to said waveguiding cores,   wherein said patterned electrodes applied to said fourth substrate comprise elongate element overlapping said low index HPDLC.   wherein said detector comprises an array of photosensitive elements, each said photosensitive element being optically coupled to at least one said core.   
     
     
         2 . The apparatus of  claim 1  wherein each said SBG element in said first and second SBG arrays is switchable between a diffracting state and a non-diffracting state, said SBG elements diffracting only said first polarization light, 
     
     
         3 . The apparatus of  claim 2  wherein said diffracting state exists when an electric field is applied across said SBG element and said non diffracting states exists when no electric field is applied. 
     
     
         4 . The apparatus of  claim 2  wherein said diffracting state exists when no electric field is applied across said SBG element and said non diffracting states exists when an electric field is applied. 
     
     
         5 . The apparatus of  claim 2  wherein at any time one element of said first SBG array is in a diffracting state, one element of said second SBG array is in a diffracting state, all other elements of said first and second are in a non-diffracting state. 
     
     
         6 . The apparatus of  claim 2  wherein an active SBG element of said first SBG array in a diffracting state diffracts incident first TIR light upwards into a first beam direction,
 wherein said transmission grating diffracts said first beam direction light upwards into a second beam direction, 
 wherein when contact is made with an external material at a point on the platen a portion of the second beam direction light incident at the point on the platen contacted by said external material is transmitted out of the platen, wherein light incident on the outer surface of the platen in the absence of said contact with an external material is reflected downwards in a third optical path, said third optical path traversing said cores, wherein an active column of said second SBG array along said third beam direction diffracts said third angle light into a second TIR path down said traversed core to said detector, wherein said first to third optical paths and said first and second TIR paths are in a common plane. 
 
     
     
         7 . The apparatus of  claim 2  wherein the output from detector array element is read out in synchronism with the switching of the elements of said first SBG array. 
     
     
         8 . The apparatus of  claim 1  further comprising an air gap between said first SBG array and said transmission grating. 
     
     
         9 . The apparatus of  claim 1  further comprising a priming layer between second SBG array device and said platen. 
     
     
         10 . The apparatus of  claim 1  further comprising at least one of said transparent electrodes and said substrates sandwiches a barrier layer. 
     
     
         11 . The apparatus of  claim 1  wherein said illumination means comprises a laser and a collimator lens. 
     
     
         12 . The apparatus of  claim 1  wherein said means for coupling light from said illumination means into said first TIR light guide is a grating. 
     
     
         13 . The apparatus of  claim 1  wherein said means for coupling light from said illumination means into said first TIR light guide is a prismatic element. 
     
     
         14 . The apparatus of  claim 1  wherein said means for coupling said second TIR light into said waveguide is a grating. 
     
     
         15 . The apparatus of  claim 1  wherein said means for coupling light out of said waveguide is a grating. 
     
     
         16 . The apparatus of  claim 1  wherein said transparent substrates are fabricated from plastic. 
     
     
         17 . The apparatus of  claim 1  wherein said transparent substrates are fabricated from a polycarbonate. 
     
     
         18 . The apparatus of  claim 1  wherein said waveguide cores are fabricated from an electrically conductive material. 
     
     
         19 . The apparatus of  claim 1  wherein said waveguide cores are fabricated from PDOT. 
     
     
         20 . The apparatus of  claim 1  wherein said waveguide cores are fabricated from CNT. 
     
     
         21 . The apparatus of  claim 1  wherein said detector is a linear array. 
     
     
         22 . The apparatus of  claim 1  wherein said detector is a two dimensional array. 
     
     
         23 . The apparatus of  claim 1  wherein said transparent electrodes are fabricated from ITO. 
     
     
         24 . The apparatus of  claim 1  wherein said transparent electrodes are fabricated from CNT. 
     
     
         25 . The apparatus of  claim 1  wherein said transparent electrodes are fabricated from PDOT. 
     
     
         26 . The apparatus of  claim 1  wherein said waveguides are fabricated from PDOT. 
     
     
         27 . The apparatus of  claim 1  wherein said SBG arrays are fabricated using a reverse mode HPDLC. 
     
     
         28 . The apparatus of  claim 1  further comprising a half wave plate array disposed above said first SBG array. 
     
     
         29 . A method of making a contact image measurement comprising the steps of:
 a) Providing an apparatus comprising the following parallel optical layers configured as a stack: an illumination means for providing a collimated beam of first polarisation light; a first SBG array device further comprising first and second transparent substrates sandwiching an array of selectively switchable SBG column elements, and transparent electrodes applied to opposing faces of said substrates and said SBG substrates together providing a first TIR light guide for transmitting light in a first beam direction; a transmission grating; a transparent substrate; a second SBG array device further comprising third and fourth substrates sandwiching a multiplicity of high index HPDLC regions separated by low index HPDLC regions and patterned transparent electrodes applied to opposing faces of said substrates; and a platen; and further comprising: means for coupling light from said illumination means into said first TIR light guide; means for coupling light out of said second SBG array device into an output optical path; and a detector comprising at least one photosensitive element; said high index regions providing waveguiding cores disposed parallel to said first beam direction and said low index HPDLC regions providing waveguide cladding; said substrates layer having a generally lower refractive index than said cores, said patterned electrodes applied to said third substrate defining a multiplicity of selectively switchable columns orthogonal to said waveguiding cores and pattered electrodes applied to said fourth substrate overlapping said low index HPDLC regions; a platen; and a detector;   b) an external material contacting a point on the external surface of said platen;   c) sequentially switching elements of said first SBG array into a diffracting state, all other elements being in their non-diffracting states;   d) sequentially switching columns of said second SBG array device into a diffracting state, all other columns being in their non-diffracting states;   e) each diffracting SBG element of said first SBG array diffracting incident first TIR light upwards into a first optical path,   f) said transmission grating diffracting said first optical path light upwards into a second optical path,   g) a portion of said second optical path light incident at said point on said platen contacted by said external material being transmitted out of said platen, portions of said second optical path light not incident at said point being reflected downwards in a third optical path, said third optical path traversing one said core,   h) an active SBG column element of said second SBG array along said third optical path diffracting said third angle light in a second TIR path down said traversed core and proceeding along a TIR path along said core to said detector,   
       wherein said first to third optical paths and said first and second TIR paths are in a common plane. 
     
     
         30 . The method of  claim 29  wherein said illumination means comprises a laser, a collimator lens. 
     
     
         31 . The method of  claim 29  wherein said means for coupling light from said illumination means into said first TIR light guide is a grating. 
     
     
         32 . The method of  claim 29  wherein said means for coupling light from said illumination means into said first TIR light guide is a prismatic element. 
     
     
         33 . The method of  claim 29  wherein said second SBG array device is optically coupled to said detector by means of a grating. 
     
     
         34 . The apparatus of  claim 29  wherein said columns of said second SBG array are switched in cyclic fashion with only one said column element being in a diffracting state at any time. 
     
     
         35 . The apparatus of  claim 29  wherein said column elements of said first SBG array are switched in cyclic fashion with only one said column element being in a diffracting state at any time. 
     
     
         36 . A contact image sensor comprising:
 an illumination means for providing a collimated beam of first polarisation light;   an SBG array device further comprising first and second transparent substrates sandwiching an array of selectively switchable SBG columns, and transparent electrodes applied to opposing faces of said substrates and said SBG substrates together providing a first TIR light guide for transmitting light in a first TIR beam direction;   a first transmission grating layer overlaying the lower substrate of said SBG array device;   a second transmission grating layer overlaying the upper substrates of said SBG array device;   a quarter wavelength retarder layer overlaying said second transmission grating layer;   a platen overlaying said quarter wavelength retarder layer;   a polarization rotating reflecting layer overlaying said first transmission grating layer;   means for coupling light from said illumination means into said SBG array device; means for coupling light out of said second SBG array device into an output optical path; and a detector comprising at least one photosensitive element;