Synergy between doping with rare earth elements and optoplasmonics for whispering gallery mode resonators

Whispering gallery mode (WGM) resonators enhance light-matter interaction due to their high quality (Q) factors, making them well suited for wide variety of applications. The material, geometry and surface of the WGM resonator can be tailored to enhance desirable optical properties. The possibilities to combine the material doping and adding optoplasmonic metal nanoparticles to create a hybrid active/passive system has not been widely explored. We have fabricated silica microspheres doped with erbium ions. These doped samples when pumped with 1470 to 1500nm source emitted at 1530 to 1560nm at a threshold of 1.6mW. Optimal concentration of Er ions is vital for generation of lasing signal, as both too high and too low concentration of Er ions incorporated into silica microspheres will not generate any lasing signal. Lasing was also observed when gold nanoparticles were deposited on the surface of the doped microsphere. Multiple depositions of nanoparticles when using lower concentration of colloidal nanoparticles solution help to suppress most of the higher order WGM modes leaving opportunity for excitation of nonlinear effect. Further research into these hybrid doped optoplasmonic resonators is being explored.