Endoscope imaging system based on spectral domain optical coherence tomography(SDOCT)is developed.Its theoretical resolutions and imaging depth are studied.According to the paraxial meridian line equation,the imaging principle of self-focusing(Gradient Index,GRIN)lens is discussed.GRIN lens whose length is 5.31 mm and diameter is 1.8 mm is designed for SDOCT scanning probe.By use of modulating transfer function,the effect of GRIN lens on imaging quality is contrasted with traditional sphere lens.By use of e...