Iron-oxide nanoparticles embedded silica microsphere resonator exhibiting broadband all-optical wavelength tunability.

In this Letter, a novel silica microsphere resonator (MSR) embedded with iron-oxide nanoparticles, which possesses broadband all-optical wavelength tunability, is demonstrated. It is generated by using in-line 1550 nm laser ablation of a microfiber with the assistance of magnetic fluid. To the best of our knowledge, this simple method of fabricating such MSRs is reported for the first time. Prominent photothermal effect is realized by the iron-oxide nanoparticles absorbing light pumped via the fiber stem, leading to a wavelength shift of over 13 nm (1.6 THz). Moreover, a linear tuning efficiency up to 0.2  nm/mW is realized. With excellent robustness and being fiberized, the spheres can be attractive elements in building up novel micro-illuminators, point heaters, optical sensors, and fiber communication modules.