Excitation of Whispering Gallery Modes in Micro-Bottle Resonator.

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Name of the Speaker: Suresh Chejarla (EE19D016)
Guide: Dr. Balaji Srinivasan
Venue/Online meeting link: ESB-244 (Seminar Hall)
Date/Time: 2nd December 2022, 9.00 am

Whispering gallery modes (WGMs) are specific resonances of a wave field that are strongly confined inside a micro-resonator, potentially providing a quality factor of 10­­6 - 10­­9. Such WGM could be used for sensing applications by trapping the particles on to the surface of the micro-resonators. Recently, microbottle resonators (MBR) have attracted much attention since it promises a customizable mode structure while maintaining a favorable Q/V ratio and good confinement. However, the excitation of WGMs in such MBRs is a challenging task and conventional approaches involve a rather cumbersome exercise of exciting these WGMs using a tapered fiber, limiting its use for only laboratory demonstrations.

We propose a novel approach to excite the WGMs in a microbottle resonator using an optical beam possessing orbital angular momentum (OAM). We observe that the helical propagation of the OAM, its azimuthally varying phase, as well as its transverse electric field profile are consistent with that of the WGM in a microbottle resonator. Such an observation is also confirmed by the similarity in the analytical solutions of the field profiles for both the high charge OAM and the WGM. We have also performed FEM/FDTD simulations to simulate the WGM in a microbottle resonator and find that the simulation results are consistent with the analytical results. We have also investigated the purity of the OAM modes that could be generated using a phase only spatial light modulator (SLM). Such results, along with a roadmap for future experiments will be discussed during this talk.