In this paper, we demonstrate a hybrid plasmonic bottle microresonator (PBMR) which supports whispering gallery modes (WGMs) along with surface plasmon waves (SPWs) for high performance optical sensor applications. The BMR was fabricated through “soften-and-compress” technique with a thin gold layer deposited on top of the resonator. A polarization-resolved measurement was set-up in order to fully characterize the fabricated PBMR. Initially, the uncoated BMR with waist diameter of 181 μm, stem diameter of 125 μm and length of 400 μm was fabricated and then gold film was deposited on the surface. Due to surface curvature, the gold film covering half of the BMR had a characteristic meniscus shape and maximum thickness of 30 nm. The meniscus provides appropriately tapered edges which facilitate the adiabatic transformation of BMR WGMs to SPWs and vice versa. This results in low transition losses, which combined with partially-metal-coated resonator, can result in high hybrid-PBMR Q’s. The transmission spectra of the hybrid PBMR are dramatically different to the original uncoated BMR. Under TE(TM) excitation, the PBMR showed composite resonances with Q of ~2100(850) and almost identical ~ 3 nm FSR. We have accurately fitted the observed transmission resonances with Lorentzian-shaped curves and showed that the TE and TM excitations are actually composite resonances comprise of two and three partially overlapping resonances with Q’s in excess of 2900 and 2500, respectively. To the best of our knowledge these are the highest Qs observed in plasmonic microcavities.
The fabrication and performance of a new optical microstub resonator is presented. The technique is simple and versatile enabling fabrication of high quality resonators. Q factors in excess of 10+6 have been demonstrated. Furthermore, active Ytterbium-doped microstub resonators are fabricated and characterized which show potential applications in fiber lasers and sensors.
We have carried out a systematic study of the effect of microtaper diameter on the spectral characteristics of bottle microresonators. By increasing the microtaper-diameter (Dt) from 2μm to 10μm results in progressively cleaner spectra. The transmission depth at resonance varies from ~15dB (@Dt=2μm) to >3dB (@Dt=10μm). The loaded Q factors were measured to be >10+6 in all cases. However, with microtaper Dt=10μm clearly-resolved single resonance peaks could be observed and free-spectral ranges could be easily identified. At some transmission resonances, we have observed LP01→LP11 mode transformation at the excitation microtaper waist, for the first time, as the resonance is scanned.
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