Quadrature-averaged homodyne detection for cavity parameter estimation

TL;DR

This paper introduces a phase-averaged homodyne detection method for cavity parameter estimation that simplifies analysis, removes the need for active feedback, and accurately characterizes cavity frequency modulations.

Contribution

The study demonstrates both theoretically and experimentally that quadrature averaging in homodyne detection improves cavity parameter estimation without active feedback.

Findings

Quadrature averaging simplifies the transduction function.

The method is robust against non-resonant channel parameters.

It enables direct measurement of cavity frequency modulation magnitude.

Abstract

Balanced homodyne interferometry is a well-known detection technique that allows for sensitive characterization of light fields. Conventionally a homodyne interferometer is operated by locking the relative phase of a reference beam to the signal beam by means of an active feedback loop. A less often used method is to perform a slow continuous modulation of the reference beam arm length that corresponds to averaging all relative phases during the measurement.Here we show theoretically and experimentally that this quadrature averaging can be advantageous in estimating the parameters of a resonant optical cavity. We demonstrate that the averaging turns the transduction function, from cavity frequency fluctuations into the interferometer signal, into a simple function of the laser detuning that, notably, does not depend on the parameters of possible non-resonant channels present in the system. The method needs no active feedback and gives results that are easy to interpret. Moreover, the phase-averaged measurement allows to characterize the absolute magnitude of a cavity frequency modulation.