The Oct Axial Superresolution

Optical coherence tomography (OCT) is an emerging modality which combines confocal scanning microscopy and low coherence interference technology. Axial resolution in optical coherence tomography (OCT) imaging is determined by the coherence length of light source and the beam-focusing condition. Currently, the most adopted approach for achieving high axial resolution in OCT is using a light source with a broaden bandwidth. In this thesis we propose an alternative method to increase the axial resolution of OCT by combining coherence gating with superresolution through an appropriate phase filter. In the proposed OCT system, 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 light source, which is nevertheless costing and inconvenient in implementation.We start off with the theory of three dimensional point spread function, analyze superresolution characteristics of amplitude filters and phase filters based on the requirement of axial superresolution in OCT system, and carry out the experiment using an assigned filter on OCT system in laboratory.Four chapters are included in this thesis. In chapter 1, the development of superresolution and the principle of OCT are introduced. The most adopted approach to increase axial resolution of OCT system is summarized and several advantages of the application of axial superresolution in OCT are presented. In chapter 2, the characteristics of point spread function near the focus are analyzed in detail based on the theory of superresolution. Different kinds of optical filters are enumerated and three factors used to evaluate the effect of superresolution are discussed. In chapter 3, the axial gains of several classical optical filters are calculated according to the requirement of enhancement of axial resolution in OCT by superresolution. Two theoretic schemes are put forward in order to actualize the axial superresolution of OCT. In chapter 4, theoretical results and laboratorial OCT system are combinedthrough a three-zone phase filter in experiment. Various factors that influence the effects of superresolution are analyzed concretely. In chapter 5, the project is summed up and further assignments about the improvement of our scheme are suggested.