An Investigation of Untapered and Tapered Fibre Transmission Properties

Abstract

This thesis is about investigation of untapered and tapered fibre transmission properties by experimentation and simulation. Tapered fibre fabricated from commercial products and custom fibre from Bath University was investigated including different fibre type, taper length, and taper ratios. Simulations of untapered and tapered fibre by consideration of geometrical optics using Zemax are presented and compared to electromagnetic waveguide simulations using COMSOL. In addition, the impact of modal noise in tapered fibre is investigated, especially graded-index tapers, by quantifying macro- and micro-bending loss. Moreover, the fabrication of build-inhouse connector tapered fibre is introduced as a robust and cost-saving tool for spectrograph link. Lastly, a tapered fibre is tested with a compact EXOplanet high-resolution SPECtrograph (EXOhSPEC) of the University of Hertfordshire using Tungsten and ThAr lamps. Although the cladding light is detected clearly in custom graded-index taper, the light throughput in EXOhSPEC is improved. Overall these results indicate the potential for reasonable fibre-fed spectrograph performance using a ’single tapered fibre’.