Optical Coherence Tomography (OCT) is an imaging technique that enables the acquisition of high-resolution, cross-sectional, real-time images of transparent scattering media. The application of swept source lasers to OCT has enabled axial acquisition rates in the MHz range, limited in the first instance by the availability of lasers with the desired spectral bandwidth (>100 nm) and high sweep rates (100s of kHz to MHz). Several important characteristics of candidate sources are readily accessible, such as the laser power, scan range and spectral flatness. The characterisation of the phase noise properties of such sources is challenging however, not least because the linewidth is expected to vary throughout the sweep. A technique based on the synchronisation of an optical gate with the sweep trigger has been described , but with resolution limited to that of an optical spectrum analyser, and with a high degree of sweep averaging.
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