Multi-Degree-of-Freedom Stabilization of Large-Scale Photonic-Integrated Circuits

We present and elaborate the principles of a novel control and calibration (C&C) systematic approach, aiming at feedback stabilization of large scale photonic-integrated circuits (PIC) to their nominal operating points in D-dimensional spaces of tuning parameters, based on refinement of extremum-seeking (ES) real-time optimization techniques. The novel methodology enables, in principle, stabilizing a large number D of tuning degrees of freedom (DOF) of PICs, with just one optical power monitoring (probe) point. The proposed C&C digital controller ports multidimensional ES stabilization concepts to photonics for the first time and further introduces novel improvements to known ES techniques, proposing a new frame-based discrete-multitone method of actuation signals generation and probe signals detection, akin to an orthogonal-frequency-division multiplexing modulation format. Another novel element is that the iterative digital algorithm adaptively selects between gradient- versus Newton-based descent and between various methods of line search. This approach enables real-time application of unconstrained optimization techniques for C&C of photonic circuits with multiple tuning DOFs. The new technique is exemplified by numeric simulations of the stabilization of a Silicon photonic microring modulator with D = 2 tuning DOFs, concurrently tuning both resonant phase and a second coupling phase parameter, optimizing critical coupling into the microring based on observing the optical power at single low-frequency monitoring point.