Optical fibre taper components

Abstract

This thesis describes the fabrication, properties and analysis of some components made from tapered single-mode optical fibres. Its greater part is concerned with the study of directional couplers made by the taper technique, and the well-known properties of these important components are summarised.

An extensive investigation into the effects of twist on tapered couplers is described. Twist is found to change (‘tune’) the output splitting ratio of couplers, an effect which is examined experimentally. The practical application of twist-tuning as the basis of a freely tunable coupler, and also as an aid in the fabrication of standard fixed-ratio couplers, is considered. The effects of twist on couplers are analysed in detail, and a simple twist-tuning law is derived, tested and criticised.

The use of a pre-polish technique for the fabrication of asymmetric tapered couplers is described. The adjustment of the maximum splitting ratio of asymmetric couplers is demonstrated, a priori by control of the coupler's cross-sectional shape, and a posteriori by twist-tuning. Questions concerning the connection between waveguide adiabaticity and loss, raised by the successful implementation of asymmetric couplers, are considered.

The effects of birefringence on the performance of the fibre Sagnac reflector, which is made by joining together the two output fibres of a coupler, are examined experimentally and analysed using Jones calculus.

Miscellaneous studies concerning single-fibre tapers are also described. These consider the fabrication and properties of tapers with rectangular cross-sections, light propagation through tapered few-mode fibres, and the effects of a tapered section of fibre on the 'fibre fuse' thermal damage mechanism.

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