Experimental observation of whispering gallery modes in novel silicon microcylindrical resonators

Microresonators that support whispering gallery modes (WGMs) are ideal systems for studying nonlinear phenomena at low thresholds due to the small mode volumes and the high quality (Q) factors and, as such, they are currently generating much scientific interest [1]. A variety of geometries have been investigated including microspheres, microdisks, toroids and micropillars, using a range of dielectrics and, more recently, semiconductor materials. One of the major challenges in fabricating semiconductor microresonators is obtaining the smooth, defect-free, surfaces required for high Q operation. In this paper, we present a novel approach to fabricating high quality silicon microcylindrical resonators starting from the silicon optical fibre platform [2]. The silicon fibres are fabricated using a high pressure chemical deposition technique to fill silica capillaries with the semiconductor material. This process can be easily modified to fill capillaries of various internal diameters with the deposited material taking on the pristine smoothness of the capillary walls (0.1 nm RMS). As an optical material, silicon is particularly attractive due to its broad transparency window that extends from the telecoms band to the mid-IR (∼1.2 - 7 μm), as well as its high optical damage threshold and large nonlinearities.