Analog-based detection method in optical low-coherence reflectometer for measurement of retardation and fast-axis angle

This study presents a novel detection method in optical low-coherence reflectometer for the simultaneous measurement of the reflectivity and birefringence characteristics of a sample. By implementing analog electronics in a standard two-channel time domain low-coherence reflectometer, the ratio of the envelope amplitude between two orthogonal interferometric signals, which is used for calculating the retardation angle, can then be analog-decoded using a differential detection scheme based on the quotient rule of a logarithmic function. The proposed method for direct retardation measurement benefits from common-mode noise suppression advantages that support efforts to improve the accuracy of phase retardation measurement. Furthermore, a full interferometric signal to extract the phase information is not needed for calculating fast-axis angle. Reductions in data acquisition rates and processing time are expected. The results from a calibrated test plate were correspondingly presented.