Optimization of the self-injection locking and resonator characterisation in this regime

摘要

Self-injection locking (SIL) is an effect of the oscillator frequency stabilization by means of a passive external high-quality cavity enabling frequency filtered coherent optical feedback to the oscillator. It is widely used in various photonic applications, including compact narrow-linewidth lasers and microcomb sources. While basic properties of this effect were studied in many theoretical and experimental works, deeper insight on its physical features and parameter space analysis allows us to build a model that describes its behavior and predicts at least an order of magnitude improvement of the stabilized laser lincwidth reduction as compared to the best previous results. We find out a global maximum over all parameters and obtain analytical expression for the optimal stabilization coefficient. Influence of the resonator non-linearity and transition from the SIL to single cavity regime arc discussed. Quality factor of the resonator appears to be a key parameter for effective SIL and oscillator stabilisation. Crystalline microresonators demonstrated the highest Q and a prism coupling is a robust method of its excitation, broadly used in applications. We developed and verified experimentally a new method of determining the key parameters of the chosen mode of the microresonator - quality factor and vertical index based on the measurement of the locking bandwidth as a function of the resonator to prism distance. Unlike other methods it allows for the measurement to be made right in the SIL regime and docs not require narrow-line lasers or fast photodetectors. A comparison with the FWHM and ringdown methods demonstrated excellent agreement.