Estimation of a parameter of a cavity on an integrated photonic chip

An apparatus comprising:

• a source of pump light configured to generate light at a pre-determined frequency;
• a system configured to introduce a shift into a phase of the light received from the source of pump light to transform the light to a phase-shifted light and to deliver the phase-shifted light to a first location;
• an optical detection system configured to receive the phase-shifted light from a second location that is different from the first location upon propagation from the first location to the second location;
• and
• electronic circuitry operably coupled with the optical detection system and configured to determine, based on parameters of said phase-shifted light registered at the second location when a resonant medium is present between the first and second locations, a coupling rate representing said resonant medium,
• wherein the resonant medium has a resonance frequency that is substantially equal to the pre-determined frequency, an input port at the first location configured to receive the phase-shifted light from the system, and an output port at the second location configured to outcouple the phase-shifted light that has traversed the resonant medium from the input port to the output port towards the optical detection system.