Interfacing whispering-gallery microresonators and free space light with cavity enhanced Rayleigh scattering

TL;DR

This paper introduces a novel nanocoupler based on cavity enhanced Rayleigh scattering that enables free-space light coupling into whispering gallery mode resonators, demonstrated through a whispering gallery microlaser with potential for compact, integrated photonics.

Contribution

The authors present a new nanocoupler scheme using cavity enhanced Rayleigh scattering, overcoming symmetry and size limitations of traditional WGMR coupling methods.

Findings

Successful free-space optical pumping of Ytterbium-doped silica microtoroid

Demonstration of whispering gallery microlaser using the new nanocoupler

Potential for integrating WGMRs into compact, solar-powered photonics

Abstract

Whispering gallery mode resonators (WGMRs) take advantage of strong light confinement and long photon lifetime for applications in sensing, optomechanics, microlasers and quantum optics. However, their rotational symmetry and low radiation loss impede energy exchange between WGMs and the surrounding. As a result, free-space coupling of light into and from WGMRs is very challenging. In previous schemes, resonators are intentionally deformed to break circular symmetry to enable free-space coupling of carefully aligned focused light, which comes with bulky size and alignment issue that hinder the realization of compact WGMR applications. Here, we report a new class of nanocouplers based on cavity enhanced Rayleigh scattering from nano-scatterer(s) on resonator surface, and demonstrate whispering gallery microlaser by free-space optical pumping of an Ytterbium doped silica microtoroid via the scatterers. This new scheme will not only expand the range of applications enabled by WGMRs, but also provide a possible route to integrate them into solar powered green photonics.