Misalignment measure error compensation in a passive phase-demodulated laser interferometer

In this paper, we present a phase error correction algorithm for passive phase demodulation in Michelson interferometers. The key feature of the passive demodulation scheme is the incorporation of a grating (Ronchi) filter placed in front of optical detector. The filter is split into four quadrants and each of the quadrants imposes a 90° phase shift. This quadrature feature offers single-step detection of phase information from the interference fringes, which are created by the superposition of the object and reference light beams. Our signal processing scheme incorporates first a diagonal subtraction, then followed by appropriate filtering and root mean square. In addition, this scheme can remove spurious intensity fluctuations induced by microphonics and unstable light source. An experimental setup has been constructed for demonstrating the operation of the proposed scheme. Simulation of possible errors due to grating misalignment and the effects on signal recovery will also be presented.