All-optical tuning of ultrahigh Q-factor microsphere resonators with graphite coating.

It is crucial to achieve large-scale and fast WGM tuning using a low-cost and simple system while maintaining the ultrahigh Q-factor of the resonator for applications. We prepared an ultrahigh Q-factor microsphere resonator with graphite coating for all-optical tuning. Microspheres were manufactured using ordinary single-mode optical fibers via the arc discharge method and then coated with a layer of graphite on top. A control laser was introduced from the tail fiber of a microsphere and irradiated onto the coating on top of the microsphere. The graphite coating could quickly absorb the energy of the control laser and cause temperature changes in the microspheres, achieving all-optical tuning. When the power of the control laser was within the range of 10 mW, the responsivity of all-optical tuning was 96 pm/mW. This type of microsphere exhibits the advantages of a simple structure, easy manufacturing, low cost, and ultra-high Q-factor.