Abstract

It has been shown previously that all four Stokes parameters of light can be measured using an arrangement of four photodetectors.¹ Three of the four detectors are partially reflective and steer the beam in a nonplanar path to the fourth absorbing detector. In this paper schemes that employ only two reflective detectors for measuring all four Stokes parameters are described. The detectors are set for oblique reflection and with noncoincident planes of incidence. Recording the 2 × 1 output signal vector for two angular positions (45° apart) of the two-detector assembly around the incident beam axis provides sufficient information to determine the 4 × 1 Stokes vector. Mechanical rotation can be avoided by using a Faraday rotator in front of a stationary arrangement of two detectors. Another novel scheme uses intermittent optical feedback, with a normal-incidence back-reflecting mirror and a light chopper, to modulate the output signals of the two detectors in a square-wave fashion. The two square waves provide enough data to determine fully the most general state of partial elliptical polarization of incident light. The appropriate instrument matrix and its determinant are derived explicitly, and all possible discrete singularity conditions are shown to be readily avoidable. Implementations in fiber-optic form are also discussed.

© 1991 Optical Society of America