WGM Photonic Molecules as a Platform for Stable Pulsed Laser Emission Generation

The WGM resonator, owing to its high Q-factor and compact structure, stands out as an ideal resonant cavity for the miniaturization of solid-state lasers. However, current research is limited to CW lasers and excludes pulsed lasers due to stricter material/structural demands of pulsed laser operation. Here, we achieved a stable Q-switched pulsed laser output using WGM microcavities fabricated from various YAG crystalline films, and we propose that WGM photonic molecules hold significant promise as a platform for generating stable pulsed laser emissions. However, this size increased the number of cavity modes, leading to multimode oscillation and making it difficult for a single WGM microcavity (i.e., the Cr,Nd:YAG microring) to generate stable Q-switched pulsed laser output. To address this issue, we constructed a WGM photonic molecule by combining the Cr,Nd:YAG microring with a YAG microdisk. By utilizing the Vernier effect within this WGM photonic molecule for mode selection, we successfully achieved stable single-mode Q-switched pulsed laser output at 1065.64 nm with a signal-to-noise ratio below 23.8 dB. This pulsed laser exhibited stable pulse emission characteristics, with a maximum repetition rate of 21.1 MHz and a minimum pulse width of 5.121 ns. This work demonstrates that, compared to a single WGM microcavity, photonic molecules offer a more convenient and effective platform for achieving stable Q-switched pulsed laser output.