Characterization of Er:ZBNA microspherical lasers

Abstract

We report here on efforts to characterise erbium-doped, heavy-metal fluoride glass microspherical lasers as a function of pump laser parameters, such as wavelength and power, and the temperature of the microsphere. The microspheres are fabricated from a novel material, ZBNA, optimised for its ability to act as a host for erbium and to favour laser emissions in the near infra-red region at 1.56 microns from the dopant. We work with microspheres that have typical diameters of ~80 microns. By attaching the microsphere to the tip of a narrow optical fibre a suitable method for manipulating the microsphere within the set-up has been developed. Pump light at 980 nm is coupled into the microsphere through evanescent wave tunnelling and propagates within the sphere in whispering gallery modes. A half-taper fibre is used as the coupling element. Strong green fluorescence at 540 nm has been observed. This indicates that the pump light is efficiently coupled into the sphere and that the alignment of the system is reasonable. We present an introduction to the fabrication of microsphere lasers, half-taper fibres and the physics of whispering gallery modes. In addition, we discuss the suitability of erbium as a lasing material when used in conjunction with the 980 nm pump light. Finally, we discuss our first experimental observations.