Improved demodulation scheme for fiber optic interferometers using an asymmetric 3×3 coupler

Problems associated with the demodulation of the signal produced by a fiber optic interferometer which employs a 3/spl times/3 fiber coupler are investigated both theoretically and experimentally. It is shown that existing demodulation methods do not work well, especially when the 3/spl times/3 coupler is asymmetric, as is often the case. Modifications to improve the performance of a previously proposed method are suggested. Furthermore, an alternative demodulation circuit is presented which is simple and which works well even when the 3/spl times/3 coupler is asymmetric.