Efficient coupling of free propagating light into Whispering Gallery Modes

Xavier Zambrana‐Puyalto ,Davide D’ambrosio ,G Gagliardi

doi:10.1051/epjconf/202125504002

Xavier Zambrana‐Puyalto , Davide D’ambrosio + Show 1 more

Open Access

https://doi.org/10.1051/epjconf/202125504002

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Abstract

Whispering Gallery Mode resonators are dielectric structures with cylindrical symmetry. They are typically excited with an evanescent field leaking out of a tapered fiber or a waveguide. It is also known that they can be excited with free propagating beams. In this work, we use a recently developed analytical model which quantitatively describes the coupling of free propagating beams into Whispering Gallery Modes for spherical particles. Using this model, we have been able to theoretically quantify the mode purity and the coupling efficiency of a resonant Whispering Gallery Mode of an order j*= 1456. We have observed that the transverse position of the beam plays a crucial role in determining the mode purity and coupling efficiency. Last but not least, we have verified that the coupling efficiency as well as the Q-factor predicted by our model are in an outstanding agreement with the experimental values measured on a microresonator of the same dimensions as the simulated one.

Highlights

Whispering Gallery Mode (WGM) resonators are dielectric structures with cylindrical symmetry
We are interested in studying the coupling efficiency (CE) as well as the mode purity (MP) of one of these resonances
We compute the MP as the scattered power given by a targeted single mode, divided by the total scattered power

Summary

Introduction

Whispering Gallery Mode (WGM) resonators are dielectric structures with cylindrical symmetry. Their sizes tend to range from ten to a few hundreds of micrometers. We have theoretically demonstrated that the WGM excitation in direct scattering set-ups is due to angular momentum (AM) matching [5]. We focus our attention on the mode purity (MP) and the coupling efficiency (CE) of the excited WGMs. we compare our theoretical predictions with the experimental data collected for a microdroplet resonator with a diameter of 300 μm. We compare our theoretical predictions with the experimental data collected for a microdroplet resonator with a diameter of 300 μm As it will be shown, the match of our theoretical and experimental data is outstanding, in terms of CE, and in terms of resonance spectrum, Q-factor of resonances, and EM field distribution

Theoretical model

Results

Conclusion