Suppression of Nonlinear Residual Intensity Modulation in Multifunction Integrated Optic Circuit for Fiber-Optic Gyroscopes

The nonlinear residual intensity modulation (RIM) in a multifunction integrated optic circuit (MIOC), mainly caused by the recoupling of the stray light of the TE mode to the output fiber, can impact the stability of a fiber-optic gyroscope (FOG). Theoretically, the polarization extinct ratio (PER) of the MIOC can be utilized to evaluate the nonlinear RIM. To suppress the nonlinear RIM, we have constructed an anti-reflection layer consisting of rough treatment and absorption coating on the bottom of the MIOC. Compared with the traditional design, the MIOC presents a lower nonlinear RIM about an order of magnitude (from 6 × 10^-4 to 8 × 10^-5), which has been verified by both theoretical simulation and practical experiments. As well as, the PER of the MIOC is improved with this design. The MIOC design proposed in this article has good potential in the applications of high-accuracy FOGs.