Whispering-gallery-mode optical resonators have shown their potentials for sensing applications in recent years owing to significantly enhanced light-matter interactions in a strongly confined volume. Boosting the sensitivity of the sensor and miniaturing the sensing system are two of the most important directions of whispering-galley-mode sensors. In this talk, I will present our recent work on novel sensing mechanism to enhance the sensitivity of a whispering-gallery-mode sensor, and a portable, wireless sensing system which can be fully controlled by smart devices. By tuning two nanoscale scatterers within the mode volume, a whispering-gallery-mode resonator can be steered to non-Hermitian degeneracies, also known as exceptional points. Due to the complex-square-root topology at the vicinity of exceptional points, the frequency splitting induced by a target object (with sufficiently small perturbation) is proportional to the square-root of its perturbation strength, and is thus larger than the frequency splitting obtained in conventional sensing schemes which is proportional to the perturbation strength of the target object. We also demonstrated that, by integrating a packaged sensor, a microcontroller, a wireless transceiver and power supply, we could build a miniature whispering-gallery-mode sensing system with a wireless interface. A customized iOS app has been developed to monitor and adjust the system parameters, and collect and analyze the sensing signals. This wireless sensing system could be employed to measure temperature distribution in a selected area. Our studies help broaden the applications of the whispering-gallery-mode resonators as an innovative sensor platform.
Whispering gallery mode (WGM) microresonators have been intensively studied in many areas such as sensing, lasing, and fundamental study. WGM microresonators are always coupled by a tapered fiber, and the coupling is controlled by a 3D nanotranslation stage. We always suffer from the instability of coupling condition, which means it is difficult to put microresonators in practical applications. Hence, we present an efficient way to package on-chip ultrahigh-Q microresonators. Stimulated Raman Scattering is achieved in this packaged microresonator, which means we have a portable, narrow linewidth laser and it can be used to expand the working wavelength of a laser. In addition, by coupling two whispering-gallery modes (WGM), which is simultaneously excited in the packaged microtoroid resonator, we can observe an electromagnetically induced transparency (EIT) effect for the first time in a portable WGM structure. This packaged microresonator can be used for real quantum communication applications. Furthermore, highly sensitive sensing can benefit from the high Q-factor and its stability.
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