Dispersion Optimization For Optical Coherence Tomography

In Optical Coherence Tomography(OCT),high speed and high resolution are always important and there are a lot of research in these areas.With higher imaging speed,wider range of samples can be detected.Also,higher imaging speed can reduce image blur caused by the movement of the sample.Higher resolution enables clearer images,so as to get more structure information of the sample.Based on the study of dispersion,this thesis proposed a novel transformation to compensate dispersion and achiev e high resolution along depth.Furthermore,for optical computing OCT(OC2T),dispersion is introduced to enable a conjugate restrained OCT high speed imaging without any data processing,achieving ?2 times higher resolution than typical OC2 T.In addition,to achieve super-resolution along depth,we also proposed a novel method to break the resolution limitation fundamentally determined by the bandwidth of the light source and obtained preliminary results.Firstly,in the Fourier-domain OCT,the interference spectrum exists distortion due to the dispersion imbalance caused by sample or the system itself.Numerical dispersion compensation method is widely used by multiplying a phase factor prior to the Fast Fourier Transform(FFT).However,this method can only compensate the dispersion of the system and the sample at a certain depth.It might fail if a depth-dependent dispersion exists.In this thesis,we proposed a novel transformation which chooses the conjugate function of the signal itself as an optimized kernel function and therefore can compensate the dispersion at all range of depth in the sample.Also,the dispersion of unknown samples can be calculated using conjugate transformation.Secondly,in the optical computing OCT,the optical computing gives an imperfect Fourier transformation,trending to increase the signal width and hence lower down the axial resolution.In this thesis,we prove that between reference and sample arm,there always exists a unique dispersion imbalance that can introduce suitable distortion into interference spectrum and achieve the resolution limit which determined by the light source.Also,by introducing this unique dispersion imbalance,the conjugate signal can be restrained.As this method does not need any post processing,to the best of our knowledge,it is the fastest method to restrain the conjugate signal for real-time imaging.Fast and complicated calculation with optical computing is also demonstrated.The methods above can achieve the resolution limit determined by the light source.While,how to break through the limit the limit is also an important research direction.In this thesis,we proposed a super resolution OCT method based on optical path stretch,enabling resolution higher than the limitation.Preliminary results are obtained.Our studies demonstrate that high speed optical computing OCT and high-resolution OCT are of great significance for the performance of OCT and will have very good prospects for future application.