Injection locking of photothermal oscillation in optofluidic microcavities

Optical microcavities, which exhibit ultrahigh quality factors and exceptional light-field confinement, have become an important platform for investigating nonlinear phenomena and developing highly sensitive sensors. Within these systems, photothermal oscillations induced by competing thermo-optic effects in multimaterial structures show considerable application potential. However, their practical implementation is severely limited by frequency drift and high phase noise. In this study, we demonstrate the first successful frequency stabilization of photothermal oscillation signals using electro-optic injection locking within an optofluidic microbubble resonator. Experimental results show that after locking, the linewidth of the frequency spectrum narrows markedly and the phase noise is reduced by more than 10 dB at an offset frequency of 10 Hz. Statistical analysis of 450 consecutive measurements reveals that the standard deviations of both the center frequency and peak power in the locked state are significantly lower than those in the unlocked state. This approach converts unstable photothermal oscillation signals into controlled outputs with narrow spectral bandwidth and improved phase stability. It, therefore, offers a promising strategy for overcoming signal instability, while preserving the ultrahigh sensitivity of microcavities, and provides a strong foundation for sensing applications such as biomolecule detection and environmental gas monitoring.