Field access techniques for single-mode fibres

Abstract

This thesis reports on the exploitation of the beam-expanding properties of tapers in single-mode fibres and on the development of a new and versatile approach to fibre polishing.

A theoretical study of the fused-taper coupler explains the differences in coupling and polarisation characteristics of strongly-fused and weakly-fused couplers in terms of the difference in tunnelling capability of TE and TM polarised waves.

A study of the application of glass capillary overjackets in the production of stable taper-based devices resulted in the realisation of the first practical tapered beam-expander for single-mode fibres and a class of couplers in which cut-off of the LP11 mode of the composite waveguide comprising the coupler waist induced a flattening of the wavelength characteristics of splitting ratio.

The operational principles and fabrication of a single-mode fibre beam-splitter is described. This new device which operates as a LP01 mode transformer exhibits wavelength independent 50:50 power splitting.

A new polishing technique in which the optical fibre is polished on a motor driven polishing wheel is reported. The polishing can be completed in less than ten minutes and polished lengths of up to 40mm are easily attainable. The technique was successfully applied to the construction of spectrally broad fibre polarisers.

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