Hollow core fibre (HCF) is a type of novel optical fibre which has lower refractive index in the hollow core than in the cladding. Total internal reflection (TIR) cannot explain the confinement of light to the core of a HCF. According to the confinement mechanism, the HCFs can be generally divided into hollow core photonic bandgap fibres and hollow core leaky mode fibres depending on their optical properties of the cladding structure. Hollow core negative curvature fibre (HC-NCF) is a kind of hollow core leaky mode fibre, which is defined by the negative curvature of the core boundary.This thesis presents my study of HC-NCFs over the last two years. My research has focused on developing low loss silica HC-NCFs and exploring the attenuation limit of HC-NCFs. Fifty different HC-NCFs were fabricated, which covered the spectral range from 800 nm to 4.5 μm. Minimum attenuations of 24.4 dB/km and 85 dB/km were measured at around 2400 nm wavelength and 4000 nm respectively, which are the best achieved in HCFs at these wavelengths to the best of my knowledge. The limits of HC-NCF attenuation were revealed by analysing the data from HC-NCFs scaled for minimum attenuation in different spectral regions.Other properties of HC-NCFs, including bending loss and dispersion, were also studied experimentally. By using white light interferometery, a low group velocity dispersion (GVD) was found in HC-NCFs, which agrees well with simulations. The bending loss of HC-NCFs was preliminarily studied by measuring the transmission spectra under different bending conditions. Significant bending loss was found when the bending radius was less than 15 cm.Numerical simulations were performed using COMSOL software to study the properties of HC-NCFs. In the simulations, it was found that the capillary thickness is the most important factor determining the attenuation of HC-NCFs. These results were used to explain the experimental results.This thesis is comprised of seven chapters. Chapter 1 and 2 supply background material that helps to understand the light guidance mechanism of HC-NCFs. My original work is presented in Chapter 3, 4, 5, and 6. Chapter 7 includes a summary and suggestions for future work.
|Date of Award||1 Nov 2013|
|Supervisor||Jonathan Knight (Supervisor)|