All-Optical Tuning of Microbottle Resonator Assisted by a Movable Probe With Magnetic Nanoparticles

We demonstrate an all-optical tunable device consisting of a microbottle resonator (MBR) and an internal movable probe based on the photothermal effect. The inner wall of MBR and probe tip are coated with magnetic nanoparticles (MNPs) for enhancing pump laser absorption efficiency. The increased temperature of MBR caused by laser-induced heat changes the effective refractive index of MBR and thus tunes the resonance wavelength of whispering gallery modes (WGMs). The simulation results reveal that the tuning efficiency can be enhanced by increasing pump laser power and decreasing the distance between probe tip and coupling position, which are verified by the experimental results. The demonstrated maximum tuning sensitivity and tuning range are 0.23 nm/mW and 3.7 nm, respectively. Moreover, the comparative experiments are conducted to investigate the influence of MNP coating on tuning performance, which reveals that the sensitivity of coated sensor is 42 times larger than that of uncoated. The proposed all-optical tuning scheme provides great potential in optical switches.