Observation of Critical Coupling in a Fiber Taper to a Silica-Microsphere Whispering-Gallery Mode System

TLDR

The study reports the observation of critical coupling in a high‑Q fused‑silica microsphere whispering‑gallery mode resonator coupled to a fiber taper. The experiment uses a high‑Q (~10⁷) fused‑silica microsphere resonator coupled to a fiber taper to achieve critical coupling. The experiment achieved extremely efficient power transfer to the high‑Q resonator, with off‑resonance scattering loss below 0.3 %, on‑resonance extinction of up to 26 dB, and demonstrated potential for applications in near‑field sensing and quantum optics.

Abstract

We present the observation of critical coupling in a high- Q fused-silica microsphere whispering-gallery mode resonator coupled to a fiber taper. Extremely efficient and controlled power transfer to high- Q ( approximately 10(7)) resonators has been demonstrated. Off-resonance scattering loss was measured to be less than 0.3%. On-resonance extinction in transmitted optical power through the fiber coupler was measured as high as 26 dB at the critical coupling point. This result opens up a range of new applications in fields as diverse as near-field sensing and quantum optics.