Characterisation of imperfections in hollow core photonic bandgap fibres

Abstract

Over the past decades, the performance of standard single-mode fibre (SSMF) has improved to the point that limited scope now exists for significant further reductions in loss and nonlinearity, which determine the fibre’s transmission capacity. Given the current 40% per annum growth in data traffic, and the fact that state-of-the-art data transmission experiments are operating close to the fundamental information-carrying limit of SSMF, there is strong interest in developing radically new fibres capable of much higher data carrying capacity. Recently, a potentially disruptive new type of fibre, the hollow-core (HC) photonic bandgap fibre (PBGF), has emerged as a credible candidate. It guides light predominantly (i.e. ~99%) in air, providing a unique set of optical properties such as ultralow nonlinearity, ultimate low signal latency, and the potential for lower loss compared to SSMF. However, to enable the application of HC-PBGFs for data transmission, the fabrication of long lengths of uniform, low-loss HC-PBGFs is essential, which had not been possible until recently. Despite empirical observations of high loss section along HCPBGFs and of more frequent fibre breaks than in conventional fibres were known, very little was known about the root cause of these issues at the start of this PhD project.

The investigation of the problems preventing the fabrication of long length of uniform, defect free HC-PBGF is the topic of this thesis. I developed and/or applied a suite of characterisation methods, such as IR side-scatter imaging, X-ray tomographic analysis and optical side scattering radiometry, aimed at identifying defects and imperfections that arise in HC-PBGFs. Through these
techniques, I studied the morphology and longitudinal evolution (e.g. formation, stabilisation and decay) of such defects, the first systematic study of this kind for HC-PBGFs. Furthermore I could backtrack their origin to well defined stages in the fabrication (e.g. preforms and canes). My observations suggest that all or at least most defects arise due to contamination or stacking errors, which are unintentionally introduced when the HC-PBGF preforms are assembled from arrays of glass capillaries. Ultimately, the methods I have developed and the findings described in this PhD Thesis helped develop ways to greatly reduce (and hopefully, in future, completely eliminate) these defects, which resulted in several breakthroughs including the achievement of the current record length of low loss HC-PBGF, i.e., a 11km long fibre with a uniform 5.2dB/km loss and more than 200nm transmission bandwidth, a factor of 10 longer length than what had been reported before the start of this project.

More information

Identifiers

ORCID for Seyed Reza Sandoghchi: orcid.org/0000-0003-2196-3167

ORCID for David Richardson: orcid.org/0000-0002-7751-1058

Catalogue record

Export record