CMOS Controller for Real-Time Stabilization and Configuration of Silicon Photonics Free-Space Receivers

We present a fully integrated CMOS architecture performing real-time reconfiguration of free-space optical receivers built in CMOS-compatible Silicon Photonics platforms. The chip comprises 8 independent channels and is used to dynamically drive the thermal actuators that set the working point of a photonic integrated circuit. Each channel includes the readout of a photodetector with 120 dB dynamic range, a digital processor implementing two integral controllers, and two 12-bit DACs driving the actuators. By connecting a pair of ASICs to the photonic chip, we controlled a binary-tree mesh of 15 Mach-Zehnder Interferometers while dissipating <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\approx 10$</tex> mW/channel. Our setup achieved a settling time of the receiver <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\leq 10$</tex> ms when starting from a random working point, and compensated for atmospheric turbulence up to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\approx 300$</tex> Hz. This architecture thus provides a scalable solution for establishing reliable free-space optical links between photonic processors of growing complexity.