Cavity-QED treatment of scattering-induced free-space excitation and collection in high-Qwhispering-gallery microcavities

Abstract

Whispering-gallery microcavity laser possesses ultralow threshold, whereas convenient free-space optical excitation and collection suffer from low efficiencies due to its rotational symmetry. Here we analytically study a three-dimensional microsphere coupled to a nano-sized scatterer in the framework of quantum optics. It is found that the scatterer is capable of coupling light in and out of the whispering-gallery modes (WGMs) without seriously degrading their high-Q properties, while the microsphere itself plays the role of a lens to focus the input beam on the scatterer and vice versa. Our analytical results show that (1) the high-Q WGMs can be excited in free space, and (2) over 50% of the microcavity laser emission can be collected within less than 1• . This coupling system holds great potential for low threshold microlasers free of external couplers.

Review Label-free detection with high-Q microcavities: a review of biosensing mechanisms for integrated devices

“…Furthermore, metal films have been shown to enhance prism-based coupling to WGMs [220]. It was also shown theoretically that a nanosized scatterer immobilized on the microresonator surface enables the efficient coupling to WGMs from a free space beam [221]. Another configuration for realizing hybrid photonic plasmonic microcavities are microring silicon resonators optically coupled to a metal microdisk located inside the ring.…”

Whispering-Gallery Sensors

“…There is still significant progress to be made in the development of WGM microresonator structures, such as deformed microresonators, 136 , 137 , 138 , 139 , 140 , 141 , 142 , 143 , 144 endoscopic sensing probes, 145 , 146 and WGM sensors in chip-based microfluidics channels. 147 Not only will these lead to further improvement in device sensitivity but they will also allow for the detection of analytes that are beyond the reach of current techniques.…”

Boundary Feedback Fiber Random Microcavity Laser Based on Disordered Cladding Structures

“…For example, laser emission is usually isotropic in the plane due to the rotational symmetry of the cavity structure in whispering gallery mode (WGM) lasers, resulting in very low collection efficiency in free space. When the cavity boundaries of microcavity lasers are partially disordered, the originally closed optical systems are more prone to be excited and coupled [24,25]. During this time, the output laser modes are stable, accompanied by improved laser efficiency, directional radiation, and tunable wavelength [26][27][28].…”