High-speed Time-stretch Optical Coherence Tomography

Supercontinuum sources have great potential in optical coherence tomography due to their ultrabroad spectra, which provide ultrahigh resolution images. High intensity noise of conventional supercontinuum sources, however, has been the limiting factor of widespread adoption, but the emergence of low noise supercontinuum sources promise to change this. In this thesis, both types of supercontinuum sources are tested in a spectrometer-based optical coherence tomography setup, where it is found that the low noise supercontinuum is able to produce the shot noise limited images, a feat that is not replicated by the conventional supercontinuum. Furthermore, the two types of supercontinuum sources are tested in a time-stretched setup, where chromatic dispersion maps each wavelength to a point in time, such that the spectral content can be detected by an ultrafast photo detector, which allows for millions of scans per second. The low-noise supercontinuum is again able to reach within close range of the shot noise limit, despite the much higher speed, but heavy spectral modulation introduces artefacts that impact the image quality, which shows the need for more research. Finally, generation of low noise supercontinuum sources in the important mid-infrared spectral region is investigated by experiments and numerical simulations, and it is demonstrated that a setup with active and passive fibres in a cascade drastically reduces the intensity noise, thereby increasing the potential of supercontinuum sources in mid-infrared
spectroscopy and imaging.