Nanosecond-Pulsed Passively Q-Switched Fiber Laser by Using Photothermal Dynamics in a Dielectric Microcavity

Thermal nonlinear effects have been extensively studied in whispering-gallery optical microcavities. Photothermal effect originating from high light power buildup in the microcavities plays an important role in various applications, such as thermal tuning, thermal detection, and thermal imaging; however, they are often limited by the slow photothermal response time. Here, we demonstrate a nanosecond passively Q-switched fiber laser via photothermal dynamics in a dielectric microcavity and reveal the nanosecond-time-scale photothermal response in the microcavity. The passive Q-switched fiber laser is realized by a novel Q-switching mechanism, which is derived from the dynamic photothermal effect in an ultrahigh-quality silica microcavity. Q-switched pulses with a duration of 25.8 ns and a repetition rate of 653 kHz are achieved, and it indicates that the photothermal response time is far shorter than a microsecond, which is much faster than conventional thermo-optic switching based on dielectric photonic structures. We also provide rigorous theoretical analyses on the photothermal effect and generated Q-switched pulses, which agree well with the experimental results. Our work demonstrates a counterintuitive feature of the photothermal effect in a dielectric microcavity that paves the way to ultrafast thermo-optic switching and pulsed lasing.