This thesis presents a novel structure composed of serially coupled double microsphere resonator (SCDMR) to reduce the non-fundamental resonances and therefore expand the resonance frequency spacing (RFS) in microsphere resonator systems. Coupled-mode theory is used to model the system and it is shown that the minimum RFS of a single 225µm microsphere is expanded from 5.2pm to 0.6nm by coupling to a 50µm radius microsphere while maintaining its high quality factor (2.14×10 8 ). It is shown that using the proposed structure in lasing application, a high-power narrow-linewidth low-threshold single-mode microsphere laser can be obtained. A model is proposed for microsphere lasers and verified by comparing its results to the experimental results published in the literature for a thulium doped tellurite glass 12.5?m microsphere laser. It is illustrated that by coupling an 11.5µm undoped microsphere to a multimode 50µm microsphere laser, single-mode operation is obtained and an output power of 208µW at 30mW pump power and the FWHM linewidth of 0.53fm are achieved. Furthermore, it is shown that by using the SCDMR in sensing application for sensing rodlike bacteria it is much easier to track the change in the bacteria surface density. Key Words WGM, microsphere resonator, RFS, coupled mode theory
