Pigtailing the high-Q microsphere cavity:?a simple fiber coupler for optical whispering-gallery modes

Abstract

We demonstrate a simple method for efficient coupling of standard single-mode optical fibers to a high-$Q$ optical microsphere cavity. Phase-matched excitation of whispering-gallery modes is provided by an angle-polished fiber tip in which the core-guided wave undergoes total internal reflection. In the experimental setup, which included a microsphere with both an input and an output coupler, the total fiber-to-fiber transmission at resonance reached 23% (total insertion loss, 6.3 dB), with loaded quality factor $Q\ge 3\times {10}^7$ and unloaded $Q\approx 1.2\times {10}^8$ at 1550 nm. A simple pigtailing method for microspheres permits their wider use in fiber optics and photonics devices.