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Periodic structures in optical fibres

Periodic structures in optical fibres
Periodic structures in optical fibres
The work presented in this thesis concerns techniques for the formation of periodic structures in optical fibres. Two different methods of producing such structures are studied in detail.

The first of these involves a breakdown mechanism (known as the 'fibre fuse') that permanently damages the core glass in a periodic manner leaving it unable to guide light. The dynamics of this mechanism are studied, with a view to controlling it for the production of interactive grating structures. It is determined that, due to a sharp rise in fibre absorption with temperature, a thermal shock-wave, with a typical thermal gradient of several hundred degrees Kelvin per micron, forms and travels along the fibre, heating the core glass to such an extent that damage occurs. The periodicity of the resultant damage arises from thermal focusing and de-focusing of light in the region of this shock-wave.

The second method makes use of the photorefractivity observed in certain germanosilicate fibres on exposure to moderate intensity blue light of wavelength ~480nm or UV light ~240nm. A single-mode fibre transmission filter is demonstrated for the first time, produced by exposing a fibre Sagnac loop mirror to 488nm holographic fringes. Average index changes are shown to occur if such fibres are exposed to spatially uniform blue or UV light, indicating that grating formation is by a different mechanism to the local charge separation which occurs in photorefractive crystals. The various characteristics of these average index changes are measured and analysed, with the conclusion that they result from defect centre formation, driven by two photon absorption with blue light, or single photon absorption with UV light. Associated birefringence changes are also measured and are exploited in a hi-bi fibre to periodically perturb the birefringence axes, producing a narrow-line transmission filter.
Hand, Duncan
4ec03bb9-57a6-468e-8722-de463f590ced
Hand, Duncan
4ec03bb9-57a6-468e-8722-de463f590ced
Russell, Philip St.J.
d4140bef-5198-49d6-a7a6-326efdaeff42

Hand, Duncan (1990) Periodic structures in optical fibres. University of Southampton, Department of Electronics and Computer Science - Optical Fibre Group, Doctoral Thesis, 210pp.

Record type: Thesis (Doctoral)

Abstract

The work presented in this thesis concerns techniques for the formation of periodic structures in optical fibres. Two different methods of producing such structures are studied in detail.

The first of these involves a breakdown mechanism (known as the 'fibre fuse') that permanently damages the core glass in a periodic manner leaving it unable to guide light. The dynamics of this mechanism are studied, with a view to controlling it for the production of interactive grating structures. It is determined that, due to a sharp rise in fibre absorption with temperature, a thermal shock-wave, with a typical thermal gradient of several hundred degrees Kelvin per micron, forms and travels along the fibre, heating the core glass to such an extent that damage occurs. The periodicity of the resultant damage arises from thermal focusing and de-focusing of light in the region of this shock-wave.

The second method makes use of the photorefractivity observed in certain germanosilicate fibres on exposure to moderate intensity blue light of wavelength ~480nm or UV light ~240nm. A single-mode fibre transmission filter is demonstrated for the first time, produced by exposing a fibre Sagnac loop mirror to 488nm holographic fringes. Average index changes are shown to occur if such fibres are exposed to spatially uniform blue or UV light, indicating that grating formation is by a different mechanism to the local charge separation which occurs in photorefractive crystals. The various characteristics of these average index changes are measured and analysed, with the conclusion that they result from defect centre formation, driven by two photon absorption with blue light, or single photon absorption with UV light. Associated birefringence changes are also measured and are exploited in a hi-bi fibre to periodically perturb the birefringence axes, producing a narrow-line transmission filter.

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More information

Published date: 1990
Organisations: University of Southampton, Optoelectronics Research Centre

Identifiers

Local EPrints ID: 399491
URI: https://eprints.soton.ac.uk/id/eprint/399491
PURE UUID: ceb91e07-85e0-48cf-852a-2d584db2a9d2

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Date deposited: 18 Feb 2017 00:24
Last modified: 13 Mar 2019 20:18

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