Real-time automatic polarization control based on golden section search and proportional endless reset-free control action.

We propose and experimentally demonstrate a real-time automatic polarization control scheme for fiber-optic systems based on golden section search (GSS) and proportional endless reset-free (PE-RF) control action. In the proposed method, we separate the orthogonal components of the incoming state of polarization of light and use one of the polarization components to generate a feedback signal such that the power in the other component is maximized. The feedback signal is applied to waveplates of an electronic polarization controller for which the required voltage signals are derived by the application of GSS and PE-RF control algorithms, implemented on an Arduino Uno R3 microcontroller. Our proposed method is simple, cost-effective, and has a fast response to mitigate polarization fluctuations in optical fiber links. We demonstrate this by maintaining stable polarization operation of binary and 4-PAM optical links consisting of 50 km optical fiber operating at 1550 nm. The proposed method maintains a Q-factor to within ±0.5 with excellent eye opening over 100 min of continuous operation.