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

Abstract

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) realtime 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.

Accurate Power-Efficient Format-Scalable Multi-Parallel Optical Digital-to-Analogue Conversion

“…An essential technology is already available to enable the proposed MPMZM: Control & Calibration of slow optical coherent fan-out/fan-in [39][40][41][42][43][44][45][46][47], since the onus of optimizing the oDAC D/A conversion 'staircase', reconfiguring the oDAC to lower-order constellations and switching between DD and COH operational modes is now assigned to the slow-rate (~kHz) control plane, mainly tuning the splitter and combiner taps and the phaseshifters in the parallel paths. More work is needed in this field, to work out off-line and on-line calibration procedures for the new MPMZM oDACs.…”

“…The other subfigures of Figure 5 depict constructions of VAR 1:3 and VAR 1:4 Splitters and Combiners. The MPMZM variable taps are implemented by tuning, in unison, the actuating phases of the constituent MZMs and PMs inside each of the 2:2 MCs, based on Control&Calibration (C&C) techniques for Photonic Integrated Circuits (PIC), techniques akin to those described in [39][40][41][42][43][44][45][46][47]. Postulating ability to accurately set the fan-out/fan-in modules, our novel analysis and design methodology for an S-way MPoDAC aims to evaluate the optimal MPoDAC parameters: the splitting and combining ratios (the taps), to either synthesize perfect target 1D constellations (COH PAM-2 B bipolar) or to maximin-optimize an imperfect unipolar constellation for DD.…”

“…This is akin to the trend of Digitally Assisted Analog Systems in ultra-high-speed RF mixed-signal electronics. In recent years there have been substantial advances in photonic C&C techniques similar to those described in [39][40][41][42][43][44][45][46][47], applicable to optical programmability. Those techniques may be directly leveraged to the MPoDAC C&C task for the taps and the path phases initialization and stabilization-to which topic a separate publication will be devoted.…”

Multiwavelength stabilization control of a thermo-optic system with adaptive reconfiguration

“…In addition, contactless integrated photonic probe (CLIPP) as input for feedback control for compact system integration was also demonstrated [12]. In 2015, Fisher et al [13] proposed a control scheme based calibration technique and extremum seeking algorithm on a large PIC incorporating ring resonators and MZI structures; however, there has been no experimental demonstration on MZI-based systems. In addition, the robustness, loop interaction and control are not analyzed and may not yield the best overall control.…”

“…The present demonstration shows the utility of the approach for dual outputs. The same technique can be extended to larger numbers of inputs and outputs, and is an alternative to other approaches such as dithering [2] and extremum seeking [13], and allows solid control theory to be applied to the problem, leading to a more robust solution with improved transient response. Future work will involve larger degrees of integration, employing schemes such as those of reference [12].…”