Rare-earth doped microlasers for microphotonic applications

Sol gels provide a highly flexible technique for preparation of both planar and non-planar oxide thin films. They also enable the incorporation of various dopants into the films. In this work we describe the application of erbium-doped solgel films to surface functionalize optical microresonators. The resulting microlaser devices are especially interesting because their emission band falls in the important 1.5 μm window used for optical fiber communications. Both microsphere and ultra-high-Q microtoroid resonators-on-a-chip were functionalized into lasers and then characterized [1]. The erbium-doped sol-gel films were applied to the resonator surface and subsequently a CO₂ laser was used to induce flow and densification of the sol-gel film on the surface. Optical quality thin films were obtained after the CO₂ laser induced anneal. By varying the doping concentration and thickness of the applied sol-gel layers in microsphere resonators, we can vary the laser dynamics so that both continuous-wave and pulsation operation are possible. Single mode performance with high differential quantum efficiency was also obtained using the ultra-high-Q microtoroid resonator. These chip-based microlasers enable integration with other optical or electronic functions [2-3].