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Femtosecond laser written diffractive optical devices

Femtosecond laser written diffractive optical devices
Femtosecond laser written diffractive optical devices
This thesis presents the development of optical diffractive and scattering-based devices fabricated by femtosecond laser direct writing. Structures investigated include waveguides, Fresnel lenses, diffractive gratings and scattering chips. Firstly, the laser induced refractive index change was estimated as 7×10−4 to 6×10−3 for writing powers of Pw=35 mW to 55 mW in silica. It was determined by fabricating waveguides and analysing their mode field diameter. A new writing method for controlling laser induced stress distribution was developed for improving the uniformity of inscribed structures and reducing laser-induced damage. A 36% diffraction efficiency improvement for a 50/50 grating was achieved compared to the standard multiscan writing technique. A two-layer Fresnel lens with a focal efficiency of 55% was also demonstrated. The writing technique was applied to create an integrated waveguide structure within multi-core fibre, thus forming a directional bend sensor, for which a sensitivity of -1.4 nm/degree was achieved. For a diffractive Fresnel lens, the design and the propagation simulation were demonstrated. For the high aspect ratio structure, Bessel beam writing has been utilised for a faster fabrication. A new method for refractive index estimation has been tested with the blazed diffractive grating. The diffraction efficiency of the grating has been investigated in both silica and lead silicate, a 57% diffraction efficiency was achieved with Gaussian beam writing. Finally, a laser-fabricated scattering chip based on induced voids was presented in this thesis, with applications as a wavemeter, spectrometer, and interferometric distance sensor. The algorithm based on the correlation and singular value decomposition has been demonstrated.
University of Southampton
Sun, Qi
66e3c3df-5a60-4927-a47a-c4f6020c2fc0
Sun, Qi
66e3c3df-5a60-4927-a47a-c4f6020c2fc0
Brambilla, Gilberto
815d9712-62c7-47d1-8860-9451a363a6c8

Sun, Qi (2021) Femtosecond laser written diffractive optical devices. University of Southampton, Doctoral Thesis, 106pp.

Record type: Thesis (Doctoral)

Abstract

This thesis presents the development of optical diffractive and scattering-based devices fabricated by femtosecond laser direct writing. Structures investigated include waveguides, Fresnel lenses, diffractive gratings and scattering chips. Firstly, the laser induced refractive index change was estimated as 7×10−4 to 6×10−3 for writing powers of Pw=35 mW to 55 mW in silica. It was determined by fabricating waveguides and analysing their mode field diameter. A new writing method for controlling laser induced stress distribution was developed for improving the uniformity of inscribed structures and reducing laser-induced damage. A 36% diffraction efficiency improvement for a 50/50 grating was achieved compared to the standard multiscan writing technique. A two-layer Fresnel lens with a focal efficiency of 55% was also demonstrated. The writing technique was applied to create an integrated waveguide structure within multi-core fibre, thus forming a directional bend sensor, for which a sensitivity of -1.4 nm/degree was achieved. For a diffractive Fresnel lens, the design and the propagation simulation were demonstrated. For the high aspect ratio structure, Bessel beam writing has been utilised for a faster fabrication. A new method for refractive index estimation has been tested with the blazed diffractive grating. The diffraction efficiency of the grating has been investigated in both silica and lead silicate, a 57% diffraction efficiency was achieved with Gaussian beam writing. Finally, a laser-fabricated scattering chip based on induced voids was presented in this thesis, with applications as a wavemeter, spectrometer, and interferometric distance sensor. The algorithm based on the correlation and singular value decomposition has been demonstrated.

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Submitted date: October 2021

Identifiers

Local EPrints ID: 467364
URI: http://eprints.soton.ac.uk/id/eprint/467364
PURE UUID: 847d4dd5-e905-4ed0-8951-cb57bcde6df4
ORCID for Qi Sun: ORCID iD orcid.org/0000-0002-0850-5463
ORCID for Gilberto Brambilla: ORCID iD orcid.org/0000-0002-5730-0499

Catalogue record

Date deposited: 07 Jul 2022 16:56
Last modified: 17 Mar 2024 07:20

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Contributors

Author: Qi Sun ORCID iD
Thesis advisor: Gilberto Brambilla ORCID iD

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