Patent ID: 7436569
Filing Date: 2008-10-14
Classification: G01J,G01N,G02B,G02F,H04B

Abstract:
1. A method, comprising: using a plurality of adjustable polarization rotators and a waveplate in an optical path to receive an input beam in an input polarization state and transmit the received input beam as a transmitted beam, wherein the adjustable polarization rotators are divided into a first group having at least one adjustable polarization rotator to be on one side of the waveplate in the optical path and a second group having at least one adjustable polarization rotator to be on the other side of the waveplate in the optical path; using an output optical polarizer in the optical path to receive and filter the transmitted beam as an output beam polarized in a direction along a polarization direction of the output optical polarizer to a photodetector which measures a power level of the output beam; controlling the polarization rotators to be at different collections of rotator settings to generate different states of polarization in the transmitted beam to measure different power levels of the output beam at the photodetector, respectively; for each collection of rotator settings for the adjustable polarization rotators corresponding to a generated state of polarization in the transmitted beam, applying presumed values for Stokes parameters of the input polarization state of the input beam and component parameters for the adjustable polarization rotators, the waveplate and the output optical polarizer in a Mueller matrix formulation for an optical system formed of the adjustable polarization rotators, the waveplate and the output optical polarizer in the optical path to compute a power level of the output beam at the photodetector; obtaining a sum of squared values of differences between computed power levels of the output beam and respective measured power levels of the output beam for the different states of polarization generated via controlling the polarization rotators to be at the different collections of rotator settings, respectively; adjusting at least one of the presumed values for Stokes parameters of the input polarization state of the input beam and the component parameters to search for a selected set of values for the Stokes parameters of the input polarization state of the input beam and the component parameters that minimize the sum; and using values for Stokes parameters in the selected set of values to represent a measured input polarization state of the input beam.