US Patent 10591756 Method and apparatus for contact image sensing

A contact image sensor having a waveguiding structure for propagating light in a first direction including, in series, a first clad medium, a first core, a switchable grating clad, a second core, and a second clad medium sandwiched by transparent substrates, patterned parallel electrode elements orthogonally traversing the waveguides, a light source, a platen and a detector. Switchable grating regions overlapped by a first voltage-addressed electrode element diffract TIR light from the first core towards the platen. Switchable grating region overlapped by a second voltage-addressed electrode element diffract TIR light reflected from the platen into a TIR path within the second core.