Novel direct UV written devices

Abstract

This thesis reports a series of developments based on UV writing of novel waveguide structures. The first section is an investigation into the production of Direct UV-written channel waveguides on the perimeter of a cylindrical substrate. Cylindrical waveguides were produced using variants of the Modified Chemical Vapour Deposition (MCVD) and Flame Hydrolysis Deposition for the fabrication of thin films on either surface of the cylinder. Three layer, buried waveguide structures were produced using three techniques, and channel waveguides Directly UV-written into one of the samples. The second section concerns the simultaneous definition of channel waveguides and Bragg grating structures in planar substrates. This new process used two overlapped, tightly focused UV laser beams to generate a ~3µm writing spot with an interference pattern within the intensity profile. Translation of the writing spot with the power set to a continuous value averages out the effect of the interference pattern, defining channel waveguides. Modulation of the intensity of the writing spot in the fabrication process results in the definition of channel waveguides and Bragg gratings at the same time. The structure of the grating is defined by the precise motion and modulation of the writing spot, a function controlled by a computer and is not an absolute function of the interference pattern. Using this Direct Grating Writing technique, grating and channel structures were written into blank photosensitive 3-layer silica-on-silicon samples producing gratings with peak reflection intensities between 0dB and >30dB. Bragg gratings with peak centre wavelength reflections spanning 488nm were written in a single fabrication run, all with equalised grating strengths. Direct Grating Writing was also used to produce a range of 2-dimensional planar structures including y-splitters and directional couplers. The gratings produced using this new technique were used to investigate sample photosensitivity and waveguide dispersion. Other results include; superimposed gratings, the superposition of a grating onto an etched structure and a Bragg grating based sensor.

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Identifiers

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

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