Robust nonlinear estimation of varying optical phase

This work presents a robust approach to estimate the continuously varying phase of an optical system. Here we extend the adaptive homodyne estimator scheme by using a nonlinear guaranteed cost robust filter in the feedback loop to improve the estimator performance. The nonlinear robust filter is designed by using a copy of the sector bounded nonlinear uncertainty present in the measurement of the adaptive homodyne estimator. Finally, closed loop simulations considering both linear and nonlinear uncertainty are performed and the results are compared with the standard Kalman filter results. Simulation results show a significant improvement using the nonlinear filter which provides a better choice for the time varying phase estimation problem.