Self-injection locking to a high-quality-factor microresonator is a key component of various up-to-date photonic applications, including compact narrow-linewidth lasers and microcomb sources. For optimal construction of such devices, it is necessary to know the parameters of the locking mode, which is a challenging task. We experimentally develop and verify an original technique based on the fundamentals of the self-injection locking effect, which allows determining the key parameters of the mode of the microresonator (quality factor, vertical index) as well as the laser diode parameters. We demonstrate that this method can be used in the spectral ranges where conventional methods are not applicable, for example, in the mid-IR. We stabilize a $2.64\mu \mathrm{m}$ laser diode by a high-$Q$ whispering gallery mode microresonator made of crystalline silicon. Using the elaborated technique, the quality factor of the microresonator is determined to be $5\times {10}^8$.

Self-injection locking of a diode laser to a high-quality-factor microresonator is widely used for frequency stabilization and linewidth narrowing. We constructed several microresonator-based laser sources with measured instantaneous linewidths of 1 Hz and used them for investigation and implementation of the self-injection locking effect. We studied analytically and experimentally the dependence of the stabilization coefficient on tunable parameters such as locking phase and coupling rate. It was shown that precise control of the locking phase allows fine-tuning of the generated frequency from the stabilized laser diode. We also showed that it is possible for such laser sources to realize fast continuous and linear frequency modulation by injection current tuning inside the self-injection locking regime. We conceptually demonstrate coherent frequency-modulated continuous wave LIDAR over a distance of 10 km using such a microresonator-stabilized laser diode in the frequency-chirping regime and measure velocities as low as sub-micrometer per second in the unmodulated case. These results could be of interest to cutting-edge technology applications such as space debris monitoring and long-range object classification, high-resolution spectroscopy, and others.

We experimentally observe a self-injection locking regime of the gain-switched laser to a high-$Q$ optical microresonator. We reveal that the comb generated by the gain-switched laser experiences a dramatic reduction of comb-teeth linewidths in this regime. We demonstrate the Lorentzian linewidth of the comb teeth of sub-kHz scale as narrow as for a nonswitched self-injection locked laser. Such a setup allows generation of high-contrast electrically tunable optical frequency combs with tunable comb-line spacing in a wide range from 10 kHz up to 10 GHz. The characteristics of the generated combs are studied for various modulation parameters—modulation frequency and amplitude, and for parameters, defining the efficiency of the self-injection locking—locking phase, coupling efficiency, and pump frequency detuning.

We demonstrate numerically the possibility of generation of vector platicons (or vector flat-top solitons) having orthogonally polarized components by the modulated pump at normal group velocity dispersion (GVD). Dynamics of this process can be controlled by pump polarization and depends on both the spectral interval between pumped modes and the difference of their free spectral ranges. We also show the possibility of the excitation of the hybrid soliton-platicon complexes (or hybrid complexes of bright and flat-top solitons) if pumped modes have alternating signs of the GVD coefficient.

Laser diodes are widely used and play a crucial role in myriad modern applications including nonlinear optics and photonics. Here, we explore the four-wave mixing effect in a laser diode gain medium induced by the feedback from the high-Q microring resonator. This phenomenon can be observed at a laser frequency scan close to the microresonator eigenfrequency, prior to the transition of the laser diode from a free-running to a self-injection locking regime. The effect opens up the possibility for generation of remarkably low-noise, stable, and adjustable microwave signals. We provide a detailed numerical study of this phenomenon proven with experimental results and demonstrate the generation of the signals in the GHz range. The obtained results reveal the stability of such regime and disclose the parameter ranges enabling to achieve it. Cumulatively, our findings uncover, to our knowledge, a novel laser diode operation regime and pave the way for the creation of new types of chip-scale, low-noise microwave sources, which are highly demanded for diverse applications, including telecommunication, metrology, and sensing.

Optical frequency combs are a unique tool for fundamental metrology, spectroscopy, and a broad spectrum of applications. High-Q microresonators serve as a promising platform for the generation of coherent frequency combs. The key characteristics that determine the properties of an optical frequency comb are the microresonator dispersion parameters. We have developed and verified an original technique that allows one to measure the dispersion coefficients with a high accuracy for both crystalline and integrated microresonators with the free spectral ranges from gigahertz to terahertz. We demonstrate the generation of a soliton optical frequency comb in an integrated microresonator pumped by a laser diode in the self-injection locking regime at a wavelength of 1.55 μm and show that its spectral characteristics closely correspond to the measured microresonator dispersion parameters.