Abstract:
Optical coherence tomography (OCT) is an established imaging modality that enables the acquisition of high resolution, cross-sectional images of biological tissues. Over the years OCT has been implemented with widely different geometries, including fiber components. Fiber-based OCT systems are advantageous in terms of compactness and portability. This thesis focuses on the development aspect of fiber-based OCT systems and presents an application of it to the field of marine biology. Fiber-based OCT systems are extremely portable, but using optical fibers often introduces a significant chromatic dispersion mismatch between the two arms of the interferometer, which unless properly compensated broadens the point-spread-function (PSF) and degrades the axial resolution. Dispersion can in principle be canceled by adjusting fiber lengths with sub-millimeter precision, but this is very impractical. We propose a novel technique by using dual-fiber stretchers that enables all-fiber tunable dispersion compensation. It also relaxes the constraint of cutting fibers with sub-millimeter precision, to coarsely matching them to within a few centimeters, making the operation of the system more flexible. Moreover, we show that this technique can also be used to compensate for sample dispersion. However, a drawback of the dual-fiber stretchers is that it introduces a residual 3rd-order dispersion term. This causes asymmetry and accentuates the sidelobes of the PSF. To resolve this, we couple the dual-fiber stretchers to a free-space time domain correlator and demonstrate independent 2nd- and 3rd-order tunable dispersion compensation. The former term is dealt through the dual-fiber stretchers, while the latter term is compensated by the correlator. This has the unique property to convert Seidel aberration coefficients into the same order dispersion coefficients, allowing us to compensate for the 3rd-order dispersion term. In the final topic of this thesis we apply OCT technology to the visualization of unique transparent tissues that are found among aquatic organisms. Whole body transparency is particularly common among animals living in the open oceans, often seasonally dominating the animal biomass. Recent studies have also shown some preliminary evidence that certain groups of lipid may be associated with achieving transparency in aquatic creatures. In this work, a feasibility study is conducted to test if OCT can be used as a tool to identify morphological features in aquatic creatures, to localize lipid spatially within the tissues and discriminate between the Different lipid types.