Polarization-sensitive spectral interferometry

Abstract

A polarization sensitive spectral interferometer apparatus and method for analyzing a sample by optical energy reflected from the sample. The polarization sensitive spectral interferometer apparatus and method determines polarization properties of the sample by optical energy reflected from the sample.

What is claimed: 
     
         1 . A polarization sensitive Optical Coherence Tomography system comprising:
 a polarization-sensitive spectral interferometer including a broadband frequency-swept laser source optically coupled to an optical spectrum analyzer, the optical spectrum analyzer optically coupled to a common-path spectral interferometer, the common-path spectral interferometer optically coupled to a Fiber-Optic Spectral Polarimetry Instrument, and the Fiber-Optic Spectral Polarimetry Instrument optically coupled to a photoreceiver.   
     
     
         2 . The system of  claim 1 , where the broadband frequency-swept laser source operates with a mean frequency of the output spectrum that varies over time. 
     
     
         3 . The system of  claim 1 , where Optical Spectrum Analyzer provides a clock signal that is used to trigger data acquisition for real-time synchronization of output intensity with optical frequency (v). 
     
     
         4 . The system of  claim 3 , where the broadband frequency-swept laser source is swept the over a wide optical frequency range and the optical frequency is optically coupled to a processor. 
     
     
         5 . The system of  claim 4 , where the broadband frequency-swept laser source is optically coupled to an input polarization state preparation optics; and the input polarization state preparation optics comprises a lens and a polarizing element; wherein the input polarization state preparation optics allows the preparation of a variety of fixed user-specified states. 
     
     
         6 . The system of  claim 5 , where the common-path spectral interferometer includes a sample beam and a reference beam that share a common optical path to provide an automatic compensation for dispersion and polarization difference in the sample and reference beams up to the sample and nearly ideal spatial overlap of reflected sample and reference beams to give high fringe visibility. 
     
     
         7 . The system of  claim 6 , where the common-path spectral interferometer includes a fiber optic circulator, a lens, a glass window as a reference, and a sample in a common path; where emitted light from the broadband frequency-swept laser source is transmitted to the fiber optic circulator, which prevents any unnecessary light loss returning to the broadband frequency-swept laser source. 
     
     
         8 . The system of  claim 7 , where emitted light inserted into one port of the circulator is transmitted to a center tap, while the reflected light from the glass window reference and sample is transmitted to the third port of the circulator to a detection path. 
     
     
         9 . The system of  claim 7 , where an end facet of the sample path illuminating fiber instead of the glass window can be used in the sample path. 
     
     
         10 . The system of  claim 2 , where the sample path is optically coupled to a probe via a fiber optic rotary junction. 
     
     
         11 . The system of  claim 9 , where the optical spectrum analyzer synchronizes the data acquisition with the optical clock transitions generated by the optical spectrum analyzer so each measured and digitized light intensity corresponds to an uniformly spaced or a known spectral component of the spectral interferogram. 
     
     
         12 . The system of  claim 11 , where processor estimates a sample phase retardation (δ(z)) and a fast-axis angle (α or θ) with the interference fringes and without knowledge of the polarization state of the incident light. 
     
     
         13 . The system of  claim 12 , where the processor determines the depth-resolved birefringence (Δn) and fast axis (α or θ) of a tissue sample. 
     
     
         14 . A method for analyzing a sample with a spectral interferometer comprising the steps of:
 directing light to the sample with at least one optical fiber of the interferometer including a polarization control element;   reflecting the light from the sample;   receiving the light with a receiver of the interferometer;   determining the polarization properties of the light reflected from the sample with a computer coupled to the receiver; and   using a clock signal to trigger data acquisition for real-time synchronization of output intensity with optical frequency (v).   
     
     
         15 . The method of  claim 14 , further comprising identifying the tissue type of the sample by the polarization properties as a function of depth from the birefringence of the sample. 
     
     
         16 . The method as described in  claim 15 , wherein the step of identifying the tissue type of the further comprises maintaining a table look-up in a memory of the computer having known information regarding tissue types and the associated birefringence; and comparing the known information of the associated birefringence properties obtained as a function of depth to the sample with the known information in the table look-up to identify the tissue type. 
     
     
         17 . The method as described in  claim 16 , wherein the directing light to the sample further comprises coupling the optical fiber to a catheter. 
     
     
         18 . The method as described in  claim 14 , wherein the step of directing light to the sample further comprises producing the light over a multiplicity of optical frequencies