In this paper, we demonstrate a fiber pigtailed thin wall capillary coupler for excitation of Whispering Gallery Modes (WGMs) of microsphere resonators. The coupler is made by fusion-splicing an optical fiber with a capillary tube and consequently etching the capillary wall to a thickness of a few microns. Light is coupled through the peripheral contact between inserted microsphere and the etched capillary wall. The coupling efficiency as a function of the wall thickness was studied experimentally. WGM resonance with a Q-factor of 1.14 x 104 was observed using a borosilicate glass microsphere with a diameter of 71 µm. The coupler operates in the reflection mode and provides a robust mechanical support to the microsphere resonator. It is expected that the new coupler may find broad applications in sensors, optical filters and lasers.


Electrical and Computer Engineering

Second Department

Nuclear Engineering and Radiation Science


National Science Foundation (U.S.)


The work was supported by National Science Foundation under the contract CMMI-1200787.

Keywords and Phrases

Microspheres; Optical fibers; Q factor measurement; Resonators; Thin walled structures; Whispering gallery modes, Broad application; Capillary wall; Coupling efficiency; Fusion splicing; Mechanical support; Microsphere resonators; Reflection modes; Wall thickness, Borosilicate glass

International Standard Serial Number (ISSN)


Document Type

Article - Journal

Document Version

Final Version

File Type





© 2013 Optical Society of America, All rights reserved.

Publication Date

01 Jul 2013