Based On The Lcd Dynamic Zoom Lens

OCT ( Optical Coherence Tomography ) is a noninvasive, high-resolution depth-resolved imaging method. Its axial (depth) resolution is determined primarily by the coherence length of light source, whereas the lateral (transverse) resolution depends on the numerical aperture of the probe beam. In principle, the axial resolution could be improved by using a light source with larger spectral bandwidth. And the use of high numerical aperture lens in the probe improves the lateral resolution. However, there is a trade-off between the high lateral resolution and focusing depth, because high numerical aperture would decreases the depth of focus in the OCT with conventional optical components. That means high lateral resolution and long focusing depth can't be produced simultaneously in standard OCT.Dynamic focusing is an effective method to keep high lateral resolution of OCT. OCT uses coherence gate to select backscattered photons for imaging reconstruction. With the method of dynamic focus, the focus point can be located in the coherence gate during the whole depth scanning. So, the lateral resolution keeps constant.In this thesis, a new way of dynamic focusing based on liquid crystal is introduced after analysis several present ways of dynamic focusing of OCT.The thesis contains five parts. The first chapter introduces the principle of OCT and present ways of dynamic focusing. The second chapter introduces the basic knowledge and optical character of liquid crystal (LC) as well as the phase modulation principle of spatial light modulator (SLM) based on LC. The third chapter discussed how to perform a fresnel lens with the principle of fresnel zone diffraction. The forth chapter design programs by MATLAB to prove the feasibility of phase modulation and adjustable focal length of LC lens, and analysis the simulation result.The fifth chapter achieves the experiment by using TN-LCD as SLM. Finally, there is summarize and prospect of the whole thesis.