Measurement method for optical retardation based on the phase difference effect of laser feedback fringes

We present a measurement method for optical phase retardation, which utilizes a phase-difference phenomenon of the feedback fringes in orthogonally polarized directions of a laser with anisotropic weak feedback. This phase difference is dominated by the measured retardation. The measurement principles are given based on the 3-mirror cavity model, and experiments are conducted with quartz waveplates (WPs). A measurement range 0 degrees-180 degrees is achieved, the uncertainty is theoretically better than 0.5 degrees, and the measurement precision can be improved further. This method does not require researchers to know beforehand the principal axes directions of the WPs, and has better anti-disturbance ability than the previous method based on laser feedback. (C) 2015 Optical Society of America