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

• Published in: IEEE transactions on circuits and systems. II, Express briefs Express briefs, 2016-10, Vol.63 (10), p.929-933
• Main Authors: Ciccarella, Pietro, Carminati, Marco, Ferrari, Giorgio, Bianchi, Davide, Grillanda, Stefano, Morichetti, Francesco, Melloni, Andrea, Sampietro, Marco
• Format: Article
• Language: English
• Subjects: Capacitance; Integrated photonics; light power monitor; microsensors; Monitoring; multichannel lock-in; Optical amplifiers; Optical sensors; Optical waveguides; Photonics; silicon photonics
• ISSN: 1549-7747; 1558-3791
• DOI: 10.1109/TCSII.2016.2538338

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.