32-Channel low-noise lock-in ASIC for non-invasive light detection in silicon photonics

In order to address the challenges posed by the growing complexity of silicon photonic chips integrating more and more photonics devices, which require tuning and reconfiguration, a 32-channel 0.35 μm CMOS ASIC for a recently developed in-line non-invasive light power monitor has been designed. By combining a low-noise front-end with a carefully optimized low-parasitic multiplexer and with two square-wave multipliers (real and imaginary components) the waveguide admittance (affected by the local light power) can be measured on chip over a 100 MHz bandwidth with 10 pS resolution in four simultaneous channels, suitable for closed-loop stabilization of photonic devices such as microring resonators. The results of the chip experimental characterization here reported demonstrate dramatic miniaturization, a 20-fold improvement in resolution and a 10-fold bandwidth extension with respect to a state-of-the-art bench-top instrumentation.