<title>Digital demodulation for passive homodyne optical fiber interferometry based on a 3 x 3 coupler</title>

Abstract

Two different types of 3 X 3 couplers, symmetric and quadrature, can be used for passive homodyne Mach-Zehnder optical fiber interferometry. The former provides intensity outputs proportional to cos(phi) that are shifted 120 degree(s) apart, and the latter linear combination of sin(phi) and cos(phi) , where (phi) is the optical phase difference between the sensing and reference arms. Many demodulation algorithms, both analog and digital, have been developed. Demodulation with both 3 X 3 couplers is simulated to determine the performance of algorithms when noise exists in the coupler outputs because of uncontrolled environmental inputs. Results of simulations and experimental evaluations of several demodulation schemes found in the literature are evaluated for comparison purposes. The simulation developed for this study can be used to evaluate different 3 X 3 coupler digital demodulation methods using experimental data as well as contrived numerical inputs.