Low-noise instrument for non-invasive monitoring of photonic integrated circuits

A compact USB-controlled impedance sensing instrument based on a low-noise analog lock-in detector combined with a pseudo-integrator front-end is presented. This system, whose design is illustrated in this paper along with the results of the experimental characterization, has been custom tailored on a novel application in the field of integrated photonics. Non-invasive light monitoring is achieved by means of the contactless measurement (through a thin dielectric SiO₂ cladding) of the variation of the conductivity of a silicon waveguide, with sub-micrometric cross-section, due to propagating infrared light. The instrument measures the sensor impedance up to 10 MHz, featuring a 16 pS conductivity resolution with a 100 ms measuring time. An example of automatic alignment of a source optical fiber to the chip facet achieved with the CLIPP systems is reported.