Stable and accurate characterization of optical microcavity using linear frequency modulation and thermal locking

Precise characterization of the quality factor (<i>Q</i>) and coupling regimes in ultra-low-loss optical microcavities represents a critical research objective. Compact optical microcavities exhibit a smaller surface area, making thermal effects non-negligible. Consequently, the heat induced by the probe light can compromise the accuracy of characterization. This paper proposes a scheme for testing microcavity performance by modulating the probe light with radio frequency (RF) signals. The RF signal is applied to a Mach-Zehnder modulator (MZM), where the carrier wave enables the microcavity to reach a state of thermal locking, while the first-order sideband is scanned across frequencies near the resonance. This scheme combines fine frequency stepping at the Hz level and thermal locking to enable both stationary and dynamic measurements with exceptional stability.