Integrated planar Bragg grating devices for advanced optical communication systems

Abstract

This thesis presents theoretical and experimental studies of planar Bragg grating devices for all-optical signal processing. Bragg gratings offer a route to realise many systems for all-optical signal processing including photonic Hilbert transformers. The fabrication of Bragg gratings in a planar format allows monolithic integration with traditional planar components and micro-heaters to realise devices with desired performance.

Photonic Hilbert transformers offer potential for a wide range of applications such as single-sideband modulation, and also provide operational bandwidths and speeds far beyond current electronic technologies. A series of experimental demonstrations of photonic Hilbert transformers based on apodised planar Bragg gratings with phase-shifts are presented. Devices implementing fractional order Hilbert transform are also investigated. Grating structures are synthesised to achieve improved spectral quality including the demonstration of devices with Terahertz bandwidths.

A direct UV grating writing technique based on phase-controlled interferometry is proposed and demonstrated to fabricate arbitrary Bragg gratings in a silica-on-silicon platform. Electro-optic phase modulation of one beam in the interferometer is used to manipulate the fringe pattern and control the parameters of Bragg gratings and waveguides. Along with the unique micron-order writing spot, modulation linearity and translation consistency ensures the desired grating apodisation profile is achieved. Furthermore, the significant improvement in fringe control results in larger grating index contrast, enabling Terahertz bandwidth devices.

Finally, the system utilising the phase controlled UV writing technique is applied to the inscription of fibre Bragg gratings. Various kinds of fibres are experimentally tested in the work. The small writing spot shows potential and significant capability to inscribe arbitrary Bragg gratings into fibre structures.

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Identifiers

ORCID for P.G.R. Smith: orcid.org/0000-0003-0319-718X

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