Path Length Coded Coherence Combination For OCT Three-dimensional Superresolution

Optical coherence tomography (OCT) is an emerging modality which combines low coherence interference technology and confocal scanning microscopy, it is widely used in the internal organization structure tomographic imaging. Resolution is one of the most important factors that measure the performance and technical level of OCT. But for OCT system, the axial resolution and traverse resolution are determined by different factors, the axial resolution is determined both by the bandwidth of the light source and the focused condition of the probe beam, and the traverse resolution is only determined by the focused condition of the sample arm of the OCT system. Currently, the most adopted approaches for achieving high axial resolution in OCT are using a light source with broad bandwidth and by combing combining coherence gating with apodization. By using an appropriate designed filter, the width of the central lobe of the axial point spread function is narrowed within the coherence gate of the light source, while its side lobes are lying outside without contributing to coherence imaging. It is in this way that we can obtain improved resolution in OCT system without recurring to broadening the bandwidth of the light source, which is nevertheless inconvenient and costing in implantation. However, the improvement of axial resolution is not so obvious and the traverse resolution is not improved with these methods.In this thesis, we introduced an approach of path length coded coherence combination, which can both improve the axial and traverse resolution in OCT system. Different effective functions are conformed by adding in a path length coding lens in the proposed OCT system, which are corresponding with different path lengths, owing to the intrinsic ability to differentiate path lengths, we can get several images of the same sample corresponding to the different effective functions simultaneously. By adding these functions through numerical controlling their relative contributions, we can finally get a compounding signal with both three dimensional superresolution. Compared with the previous approaches, path length coded and compounding method is very easy to operate and its cost is very low, which not only can avoid the costing and inconvenient in implantation, but also can both increase axial and traverse resolution simultaneously.We start off with the character of OCT system structure and the theory of three dimensional point spread function, theoretically prove the availability of path length coded and combination, design the two-zone path length coded lens and three-zone path length coded lens and numerical control the relative contributions, we can finally get a compounding signal with both three dimensional superresolution. According to these theory and OCT system, we simulate the imaging process of two-zone path length coded and combination and analyze the relative influence factors. At last, we carry out the experiment using the two-zone lens on SD-OCT system in laboratory.