Broadband sources and fibre delay line for the functionality enhancement of optical coherence tomography application

Abstract

The usage of supercontinuum sources has enabled a significant improvement of tomographic imaging in optical coherence tomography (OCT) systems. However, because of the intensity noise, the clarity of the OCT image can be sacrificed even though much finer axial resolution can be obtained when using this technology. Using a commercial supercontinuum SC450 (Fianium, UK) source, its performance in terms of its interference signal shape and its relative intensity noise (RIN) was compared with two other broadband sources, a semiconductor optical amplifier (SOA) and an erbium-doped fibre amplifier (EDFA). As a measure of axial resolution in OCT; by using different grating filters the full width at half maximum (FWHM) of the interference signal and the RIN figure for each source is analysed. The measured RIN value for the SC450 is found to be between ~26.8 dB and ~30.5 dB times noisier, in terms of power fluctuation, when compared to the SOA and EDFA. The development of a time-domain OCT system was also highlighted in this thesis. The OCT system can be used to perform a meaningful scan on small and thin transparent samples. An OCT image of a mirror sample was presented, taken using full bandwidth of the SOA source. Later, the SOA was amplified at higher driving current when scanning a biological sample and the OCT image of an onion skin was successfully constructed. Problems encountered during this research project were also highlighted and future work to be done to try to overcome these were also outlined.

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