Integrated end-to-end instrumentation for the study of whispering gallery modes in dynamic liquid micro-cavities coupled to sub-micron tapered fibers

Meenakshi Gaira,C.S Unnikrishnan

doi:10.1140/epjti/s40485-020-00062-3

Meenakshi Gaira, C.S Unnikrishnan

Open Access

https://doi.org/10.1140/epjti/s40485-020-00062-3

Copy DOI

Abstract

An integrated table-top facility with the end-to-end instrumentation for the study of high-Q Whispering Gallery Modes in solid and liquid micro-cavities is described, with emphasis on the in situ fabrication of reliable tapered fibers of sub-micron waist sizes for coupling light into time-dependent liquid micro-cavities. The experimental parameters have been chosen to get nearly adiabatic tapers, with their waist size consistent with the theoretical model. The oscillations in the transmitted power during fiber tapering are monitored to check the coupling of higher order modes and identify the point when the fiber is suitable for pure single mode coupling. The fabricated tapered fibers have greater than 85% transmission on the average and very good polarization fidelity. The tapered fibers have been used for efficiently exciting and detecting WGMs of Q∼107 in silica microspheres and of Q up to 7×107 in microdrops of silicone oils. The set-up is suitable for conversion to a transportable system, for sensing applications involving WGMs in liquid microdrops.

Highlights

Whispering Gallery modes (WGMs) are the eigenmodes of cylindrically symmetric cavities which get excited when evanescently coupled light gets trapped due to continuous total internal reflections and after orbiting the cavity, it returns to its starting point in phase
The facility is self-contained and dust-protected with the modular setups for fabrication of micro-cavities and tapered fibers, and for exciting WGMs in solid and liquid micro-cavities, which are all built on a single floated optical table and inside a custom-designed laminar flow assembly
We have explained in detail the fabrication and performance analysis of tapered fibers of submicron waist sizes

Summary

Introduction

Whispering Gallery modes (WGMs) are the eigenmodes of cylindrically symmetric cavities (like spheres, disks, toroids, etc.) which get excited when evanescently coupled light gets trapped due to continuous total internal reflections and after orbiting the cavity, it returns to its starting point in phase. Thereafter, tapered fibers have been widely used for efficiently and selectively exciting WGMs in different kinds of solid micro-cavities like microspheres [7, 11], micro-toroids [3, 12], microdisks [2], etc These tapered-fiber coupled solid micro-cavities have applications such as sensors ( biological [7], physical [29], chemical [30] and mechanical [31]), micro-lasers [32], cavity optomechanical oscillators [5], photonic filters and switches in Wavelength Division Multiplexed (WDM) systems [10, 33], in generation of optical frequency combs [34] and solitons [35], etc. These tapered-fiber coupled solid micro-cavities have applications such as sensors ( biological [7], physical [29], chemical [30] and mechanical [31]), micro-lasers [32], cavity optomechanical oscillators [5], photonic filters and switches in Wavelength Division Multiplexed (WDM) systems [10, 33], in generation of optical frequency combs [34] and solitons [35], etc. (Ref. [1] and [10] give detailed reviews of applications)

Methods

Findings

Conclusion