System analysis of a common-path heterodyne polarimeter

Abstract

We proposed a polarimeter combining the common-path heterodyne interferometry (CPHI) with a half-wave plate. When the azimuth of the wave plate is at 22.5 degrees, it has the best resolution for optical rotation (OR) measurement. The purpose of this paper is to analyze all possible sources of error in the system. The retardation closer to the true half wavelength, the higher the resolution will be. A large phase change of the test signal relative to the reference signal can be found by a lock-in amplifier. The system phase error is approximately 0.06∘. The accuracy of optical rotation is 1.0 × 10−3 degrees for the phase retardation is 178.08∘. The concentration resolution can reach 1.6×10−3[gdl] for fructose solutions. The magnitude of the phase error depends on the stability of the optical system and whether the two interfering lights coincide exactly. If the phase error can be reduced to 0.01∘, the resolution of OR can be increased to 1.3×10−4∘.