Integrated mixed-signal optoelectronic system-on-a-chip sensor

A mixed-signal optoelectronic system-on-a-chip sensor was integrated with embedded photodetector arrays and interferometric optical waveguides on a silicon (Si) complementary metal oxide semiconductor (CMOS) circuit chip. Photodetector (PD) arrays were fabricated with parallel mixed-signal delta-sigma (ΔΣ) analog-to-digital converters (ADC) using a standard 1.5 μm n-well Si CMOS process. The electrical and optical sensitivities of the circuit were measured and the data suggests that the circuit can detect 100 pW optical power. On the fabricated 4.6×4.7 mm² chip, interferometric optical waveguides were integrated, and the complete system was a miniaturization of a Mach Zehnder interferometer-based sensor system. The integrated sensor micro system was tested with water vapor and the multimode interference pattern changes at the output of the interferometer were observed with the on-chip photodetector and ADC array.