Fabrication of Ultra Low Loss Optical Fibre Tapers and Spherical Microresonators

Abstract

In this thesis we investigate the design and fabrication of optical fibre tapers and optical whispering gallery mode microspheres. Fabrication of the optical fibre tapers have successfully been demonstrated in exponential shaped tapers. These tapers are produced by maintaining a constant heat zone of the flame-brushing technique. Other shapes have also been investigated such as reciprocal and linear profile tapers. Tapers as small as 460 nm in diameter have been fabricated. Our tapers are proven to be low loss with 98% transmission, and can survive high humidity ( 40% RH) for 2 days. The ability to fabricate well-defined tapers has opened the window into fabrication of microspheres from fused silica. Surface tension induced from melting the tip of the fibre produces near perfect spherical shape microresonators. We have developed a technique that uses varying diameters of the tapers to produce a wide range of microsphere diameters. Microspheres with diameter from 40-400 m are demonstrated. We finally demonstrate a linewidth reduction application when using a microsphere cavity (of diameter 76 m coupled from a 1 m radius fibre taper) where this cavity is embedded into an external cavity. The linewidth of a single mode lasing was found to be 600 Hz.