IEEE J. Sel. Top. Quantum Electron. 20, 8201710 (2014)

In large-scale photonic integration, it is important to perform circuit monitoring and feedback control of devices to counteract fabrication tolerances, environmental fluctuations and crosstalk effects. An on-chip non-invasive detector that could inspect the light inside optical waveguides without altering its propagation state would be very useful for this purpose. Now, Francesco Morichetti and co-workers in Italy and the UK have demonstrated exactly that. Their contactless integrated photonic probe (CLIPP) is a few hundred micrometres in size and is fabricated on a silicon photonic platform that is compatible with complementary metal–oxide–semiconductor technology. The device works by monitoring the change in the waveguide conductance induced by the interaction of photons with intra-gap energy states localized at the waveguide's silicon–silicon oxide interface. Capacitive access to the waveguide is exploited to avoid direct contact with the waveguide core. Measurements with a dynamic range of 40 dB and a sensitivity as low as −30 dBm in waveguides and high-Q resonators were reported. The probe could prove useful for various applications, including telecommunications, optical interconnects, biosensing, and quantum manipulation and computing.