Method and apparatus for measuring polarization sensitivity of optical devices

TLDR: In this article, the distortion of the light beam polarization caused by a single-mode optical fiber is corrected by introducing two different linearly polarized light beams and measuring Stokes parameters which are used to construct a calibration matrix that is inverted and multiplied times measured Stokes parameter of subsequent measurements to yield true stokes parameters.

Abstract: An instrument includes a polarized optical source for producing three sequential predetermined states of polarization of a light beam and an optical polarization meter for measuring the polarization of a portion of the light beam transmitted by or reflected from an optical network by splitting it into four beams, passing three of the beams through optical elements, measuring the transmitted intensity of all four beams, and calculating Stokes parameters. The light beam enters the optical polarization meter through a single-mode optical fiber that acts as a spatial filter for controlling the position and alignment of the beam with respect to the optical elements. The distortion of the light beam polarization caused by this optical fiber is corrected by introducing two different linearly polarized light beams and measuring Stokes parameters which are used to construct a calibration matrix that is inverted and multiplied times measured Stokes parameters of subsequent measurements to yield true Stokes parameters. The three sequential predetermined states of polarization yield three corresponding Jones input vectors, and the Stokes parameters for the responses of the optical network are converted to three Jones output vectors. A Jones matrix for the optical network to within a complex constant is then computed from the Jones input and output vectors. Relative polarization sensitivity can be determined from this matrix for the optical network. The relative distortion caused by the optical network can be corrected by multiplying by the inverse of the matrix during later measurements through the optical network. Additionally, power measurements on the optical network and a substituted optical through enable absolute determinations and corrections.