Four-wave mixing in a laser diode gain medium induced by the feedback from a high- <i>Q</i> microring resonator

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.