Impedance-Sensing CMOS Chip for Noninvasive Light Detection in Integrated Photonics

A 100-MHz-bandwidth multichannel instrument-on-chip for noninvasive light monitoring in photonic circuits by means of the impedance sensing of the waveguide (WG) conductance variation is presented. The low-noise front-end allows accessing the WG conductance with very high sensitivity and tracking its variation upon changes of the photon flux with a resolution better than 10 pS, i.e., down to -30 dBm in optical intensity. Each electronic chain features a capacitive-feedback amplifier with a bias-handling network based on subthreshold transistors, showing -50-dBc harmonic distortion at up to few nanoamperes of input leakage current and double-balanced square-wave demodulators incorporating a low-pass limiter. To downscale the area consumption, four 8× multiplexers have been designed to address a total of 32 different optical probes, featuring a 4× MOS multiplexer cell to drop out off-phase spurious injections. The ASIC opens the way to multipoint monitoring and reconfiguration in photonic systems with many sensing sites, demonstrating the suitability of this solution for the closed-loop control of complex photonic circuits.