Method and apparatus for polarization-sensitive optical coherence tomography

Abstract

A method and apparatus for extracting the vector optical properties of biological samples with micron-scale resolution in three dimensions, using polarization-sensitive optical coherence tomography (PS-OCT). The method measures net retardance, net fast axis, and reflectivity. Polarization sensing is accomplished by illuminating the sample with at least three separate polarization states, using consecutive acquisitions of the same pixel, A-scan, or B-scan. The method can be implemented using non-polarization-maintaining fiber and a single detector. This PS-OCT method reported measures fast axis explicitly. In a calibration test of the system, net retardance was measured with an average error of 7.5° (standard deviation) 2.2° over the retardance range 0° to 180°, and fast axis with average error of 4.8° over the range 0° to 180°.

1 .- 8 . (canceled) 
     
     
         9 . A retrofit apparatus for an optical coherence tomography (OCT) system, comprising:
 a polarizer; and   a polarization adjusting device positionable in the sample arm of the OCT system, where the polarization adjusting device is configured to make the OCT system polarization sensitive.   
     
     
         10 . The apparatus of  claim 9 , where the polarizer comprises a linear polarizer. 
     
     
         11 . The apparatus of  claim 9 , where the polarization adjusting device comprises an addressable waveplate. 
     
     
         12 . A method of retrofitting an optical coherence tomography (OCT) system, comprising:
 inserting a polarization state determining apparatus in the sample arm of the OCT system, where the polarization state determining apparatus is configured to make the OCT system polarization sensitive.   
     
     
         13 . The method of  claim 12 , where the polarization state determining apparatus is configured to determine the polarization state of incident illumination probing a sample and a corresponding polarization state for detection of remitted electromagnetic energy from the sample. 
     
     
         14 . The method of  claim 12 , comprising placing a polarizer and a polarization adjusting device in the sample arm. 
     
     
         15 . The method of  claim 14 , comprising placing a linear polarizer and a wave plate in the sample arm. 
     
     
         16 . The method of  claim 14 , comprising maintaining the reference arm of the OCT system in the same configuration. 
     
     
         17 . A method of making polarization sensitive optical coherence tomography measurements, comprising
 directing light from a source to a delay line and to a sample while selectively determining the polarization state of light directed to the sample,   combining light received from the delay line and light from the sample, and   detecting the combined light.   
     
     
         18 . The method of  claim 17 , comprising characterizing the sample by mathematically analyzing the information from the detected combined light. 
     
     
         19 . The method of  claim 17 , where directing light from a source to a delay line comprises directing the light without substantially altering a polarization state of the light. 
     
     
         20 . The method of  claim 17 , comprising selectively altering the polarization state of the light directed to the sample. 
     
     
         21 . The method of  claim 20 , comprising providing polarized light to a waveplate and adjusting the waveplate. 
     
     
         22 . The method of  claim 21 , comprising providing linear polarized light to the waveplate, and adjusting the optical characteristics of the waveplate to change polarization state of light incident on the sample. 
     
     
         23 . (canceled) 
     
     
         24 . A method, comprising:
 presenting measured data from an OCT device according to an HSV color scale such that three parameters are used and plotted, whereby reflectance is mapped into saturation and value and retardance is mapped into hue.   
     
     
         25 . A method of making polarization sensitive optical coherence tomography (OCT) measurements, comprising:
 directing light from a source to a delay line and to a sample while selectively determining the polarization state of light directed to the sample;   combining light received from the delay line and light from the sample;   detecting the combined light; and   based on the detected combined light, calculating (i) total reflected power, (ii) net retardance, and (iii) net fast axis for at least three different polarization states.   
     
     
         26 . The methods of  claim 25 , where directing light from a source to a delay line comprises directing the light without substantially altering a polarization state of the light. 
     
     
         27 . The method of  claim 25 , where directing light from a source to a sample comprises selectively altering the polarization state of the light directed to the sample. 
     
     
         28 . The method of  claim 27 , comprising providing polarized light to a waveplate and adjusting the waveplate. 
     
     
         29 . The method of  claim 28 , where providing polarized light to the waveplate comprises providing linear polarized light to the waveplate, and where adjusting the waveplate comprises adjusting the optical characteristics of the waveplate to change polarization state of light incident on the sample. 
     
     
         30 . The method of  claim 25 , comprising combining light from the delay line with light from the sample having substantially the same polarization state as the light illuminating the sample. 
     
     
         31 . A method of generating an optical coherence tomography (OCT) image, comprising:
 directing light from a source to a delay line and to a sample while selectively altering the polarization state of the light directed to the sample;   combining light received from the delay line and light from the sample;   detecting the combined light; and   based on the detected combined light, presenting measured data according to an HSV color scale such that three parameters are used and plotted, where reflectance is mapped into saturation and value and retardance is mapped into hue.   
     
     
         32 . The method of  claim 31 , where selectively altering the polarization state of the light directed to the sample comprises providing polarized light to a waveplate and adjusting the waveplate. 
     
     
         33 . The method of  claim 32 , where providing polarized light to a waveplate comprises providing linear polarized light to the waveplate, and where adjusting the waveplate comprises adjusting the optical characteristics of the waveplate to change polarization state of light incident on the sample. 
     
     
         34 . The method of  claim 33 , comprising combining light from the delay line with light from the sample having substantially the same polarization state as the light illuminating the sample. 
     
     
         35 . A method of examining tissue of interest using an optical coherence tomography (OCT) system having a light source, a reference arm that has neither a polarizer nor an addressable waveplate, a sample arm having a polarizer and an addressable waveplate, and a single detector, the method comprising:
 sequentially directing light having at least three incident polarization states from a source to a delay line and to a sample,   for the at least three incident polarization states, combining light received from the delay line and light from the sample,   detecting the combined light using a single detector; and   for the at least three polarization states, calculating (i) total reflected power, (ii) net retardance, and (iii) net fast axis based on the detected combined light.   
     
     
         36 . The method of  claim 35 , comprising:
 encoding polarization data in a light signal amplitude.   
     
     
         37 . The method of  claim 36 , where encoding the polarization data includes directing light through a polarizer and an adjustable waveplate before and after the light reaches the sample. 
     
     
         38 .- 42 . (canceled)