PhD Oral Exam - Tabassom Hamidfar, Physics
When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.
Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.
Sensing with optical whispering gallery modes (WGMs) is a rapidly developing detection method in modern micro uidics research. This method explores the perturbations of spectra of WGMs propagating along the wall of an optical microresonator to characterize the liquid medium inside it. Out of the many available types of WGM microresonators, the surface nanoscale axial photonics (SNAP) platform enables fabrication of resonant ultralow loss photonics structures at the surface of an optical ber with unprecedented precision currently approaching 0:1 angstroms. In this work, rst we explore a new technique for the creation of SNAPs, by using a regular hydrogen-oxygen torch, which requires less equipment than current techniques. The transmission spectra shows that light can be fully localized by pulling a ber, with very low loss resonant modes. We then present the rst demonstration of a platform with potential for micro uidic sensing based on SNAP microresonators fabricated in silica capillary ber with ultra-thin walls by local annealing with a focused CO2 laser and internal etching with hydro uoric acid. This demonstration paves the groundwork for advanced micro uidic sensing with SNAP microresonators.
Finally, we show that light circulating in a silica microcapillary can be fully localized by evanescent coupling to a water droplet forming a high Q-factor microresonator. The discovered phenomenon suggests a novel method for micro uidics sensing and a new type of tunable resonant micro uidic-based photonic devices.