Liquid crystal fourier transform imaging spectrometer

Abstract

A hyperspectral imaging system has a processor to receive hyperspectral imaging parameters and produce a series of images to be acquired at a series of retardances at a series of retardance times, a hyperspectral imaging component having an input polarizer to polarize an incoming beam of light, a liquid crystal variable retarder to receive the polarized beam of light and to produce wavelength-dependent polarized light, an output polarizer to receive the wavelength-dependent polarized light and to convert polarization state information into a form detectable as light intensity, a voltage source connected to the liquid crystal variable retarder, and a retardance controller. The retardance controller receives the series of retardances at a series of retardance times and produces a series of voltages at a series of voltage times to apply to the liquid crystal variable retarder. A focal plane array, synchronized with the retardance controller, receives the light in a form detectable as light intensity and converts the light to a series of images.

1 - 35 . (canceled) 
     
     
         36 . A hyperspectral imaging system, comprising:
 a processor configured to receive hyperspectral imaging parameters and to determine a series of retardances at a series of retardance times based on the hyperspectral imaging parameters;   a hyperspectral imaging component comprising:
 at least one input polarizer, wherein the input polarizer receives and polarizes an incoming beam of light; 
 a liquid crystal variable retarder arranged adjacent the input polarizer opposite the incoming beam of light to receive the polarized beam of light from the input polarizer and to change polarization of the light to produce wavelength-dependent polarized light; 
 an output polarizer arranged to receive the wavelength-dependent polarized light and to convert polarization state information of the light into a form detectable as light intensity; and 
 a retardance controller configured to compute a voltage series that controls the retardance of the liquid crystal variable retarder; 
   a focal plane array synchronized with the retardance controller and configured to receive the light in a form detectable as light intensity as a function of retardance of the liquid crystal variable retarder and to convert the light to an electrical output signal that represents a series of images, the processor configured to perform transformations of the series of images to hyperspectral image data; and   wherein the liquid crystal variable retarder comprises a liquid crystal cell having spacers between substrate layers of the cell, the spacers disposed within a clear aperture of the liquid crystal cell.   
     
     
         37 . The hyperspectral imaging system of  claim 36 , wherein the processor resides in a host system and the hyperspectral imaging component resides in an add-on module to the host system. 
     
     
         38 . The hyperspectral imaging system of  claim 36 , wherein the focal plane array resides in a host system and the hyperspectral imaging component resides in an add-on module to the host system. 
     
     
         39 . The hyperspectral imaging system of  claim 36 , further comprising imaging optics arranged between the incoming beam of light and the focal plane array. 
     
     
         40 . The hyperspectral imaging system of  claim 36 , further comprising at least one light source arranged adjacent to the at least one input polarizer such that light from the light source reaches the focal plane array. 
     
     
         41 . The hyperspectral imaging system of  claim 40 , further comprising a photodetector arranged adjacent to the focal plane array and positioned to receive light from the at least one light source through the liquid crystal variable retarder. 
     
     
         42 . The hyperspectral imaging system of  claim 36 , further comprising a waveplate between the at least one input polarizer and the output polarizer. 
     
     
         43 . The hyperspectral imaging system of  claim 36 , further comprising a retardance compensation device between the at least one input polarizer and the output polarizer. 
     
     
         44 . The hyperspectral imaging system of  claim 36 , further comprising a retardance extractor. 
     
     
         45 . The hyperspectral imaging system of  claim 36 , further comprising at least one temperature sensor that provides temperature information of the liquid crystal variable retarder to the retardance controller, wherein the temperature sensor comprises a patterned electrode of a liquid crystal cell. 
     
     
         46 . The hyperspectral imaging system of  claim 36 , further comprising a clock connected to the processor and the retardance controller. 
     
     
         47 . The hyperspectral imaging system of  claim 36 , wherein at least one of the polarizers is switchable between a first state that transmits one polarization and blocks an orthogonal polarization, and a second state that transmits the one polarization and the orthogonal polarization. 
     
     
         48 . The hyperspectral imaging system of  claim 39 , wherein the liquid crystal cell resides away from the focal plane array such that rays of light that pass through the imaging optics experience a same thickness of the liquid crystal cell before striking the focal plane array and are blurred in an area in which the spacers occlude the light. 
     
     
         49 . The hyperspectral imaging system of  claim 36 , wherein the at least one input polarizer comprises a polarizing beam splitter. 
     
     
         50 . The hyperspectral imaging system of  claim 49 , further comprising a second liquid crystal variable retarder, a second output polarizer and a second focal plane array, arranged with respect to the polarizing beam splitter, wherein image light entering the polarizing beam splitter through a first port has a first polarization direction and image light entering the polarizing beam splitter through a second port has a second polarization. 
     
     
         51 . The hyperspectral imaging system of  claim 49 , further comprising a calibration light source, wherein light from the calibration light source is directed to an entrance port of a polarizing beam splitter with polarization orthogonal to that of an entrance port pointing at scenery to be imaged. 
     
     
         52 . The hyperspectral imaging system of  claim 36 , wherein the liquid crystal variable retarder comprises one of a ferroelectric liquid crystal material or a polymer network liquid crystal. 
     
     
         53 . The hyperspectral imaging system of  claim 36 , wherein the voltage series is configured to provide a two-component electric field, a first component of the two-component electric field causing liquid crystal material of the liquid crystal variable retarder to align substantially perpendicular to layers of the liquid crystal cell and a second component of the two-component electric field causing the liquid crystal material to align substantially parallel to the layers of the liquid crystal cell. 
     
     
         54 . A method of producing hyperspectral image data, comprising:
 receiving a set of hyperspectral imaging parameters at a processor;   generating, with the processor, a series of retardances at a series of retardance times corresponding to the hyperspectral imaging parameters;   sending the series of retardances at the series of retardance times to a retardance controller;   generating, with the retardance controller, a series of voltages at a series of voltage times to be applied to a liquid crystal variable retarder;   applying the series of voltages at the series of voltage times to a liquid crystal variable retarder;   capturing a series of images through the liquid crystal variable retarder with a focal plane array; and   using the processor to generate hyperspectral image data from the series of images.   
     
     
         55 . The method of  claim 54 , wherein applying the series of voltages to the liquid crystal variable retarder comprises applying a two-component field.