Simple three-stage control scheme achieving interrupt-free integrated polarization stabilization

It is a long-outstanding challenge to achieve low-complexity interrupt-free integrated polarization stabilization of infinitely changing light. Integrated phase shifters have finite tuning range and experience abrupt switching or reset when reaching the limits of their tuning ranges during the polarization stabilization process. We propose a three-stage interrupt-free integrated polarization stabilization scheme with nested electronic-photonic loops (NEPL) and dimensionality reduction (DR) method. Based on the NEPL structure, only three Mach-Zehnder interferometer (MZI) stages are needed to achieve interrupt-free polarization stabilization scheme. The input state is first constrained into a predetermined range using a nested loops with the first MZI stage and then processed by regular two-stage scheme. Throughout the entire operation, all phase shifters are tuned continuously without any pause, abrupt switching or reset. Furthermore, a DR method is introduced to reduce the control complexity and enhance control speed and accuracy of the regular two-stage scheme. A detailed analysis of the proposed design is provided, and its effectiveness is verified using electronic-photonic co-simulation in the Cadence platform. This scheme consists of only phase shifters, couplers and photodiodes (PDs) with simple electronic controllers, and can be implemented in various material systems and process platforms. To the best of our knowledge, this is the first three-stage interrupt-free polarization stabilization scheme reported in the literature.