Polymer optical fiber based active and passive whispering gallery mode resonators for microlasing and sensing applications

Abstract

In modern optics, optical microcavities are a vitally important class of tools to store light by resonant recirculation. The optical microcavities have found a wide range of applications in lasers, sensors, harmonic generation, filters and switches. High reflectivity mirrors and a decrease in the cavity length are the main factors that ensure better light confinement within an optical cavity. Achieving these requirements is extremely difficult and expensive for the mirror based resonators like Fabry-Perot cavity which eventually results in a low Q factor. Difficulty in miniaturization and assembly are other drawbacks of mirror based resonators. However, a whispering gallery mode (WGM) optical resonator can easily fulfill these requirements. WGM resonators are monolithic dielectric optical resonators with circular geometry. Extremely high Q factor and small size of WGM resonator ensure effective light confinement. Dielectric structures and liquid droplets with circular cross-sections and smooth boundaries can trap light and generate WGM resonances. WGM resonators are typically fabricated using liquid and solid materials having good optical quality. The optical performance of the WGM resonator mainly depends on the surface smoothness and optical losses of the material. Most of the WGM resonators are made up of silica fabricated by melting glass or by the sol-gel process. newlineCompared to liquid, silica, and semiconductor-based WGM cavities, polymer-based WGM cavities have many advantages including mechanical flexibility, ease of fabrication, low manufacturing temperature and cost-effectiveness. The polymer is an ideal host material for organic dyes due to its low manufacturing temperature. Dye doped polymer WGM cavities have shown great promise for the realization of flexible photonic circuits. There are several methods for the fabrication of dye-doped polymer fiber including direct drawing from dye-doped polymer solution, electrospinning and heat drawing from dye doped polymer preform.