A theoretical model for the micron resolution spectral domain optical coherence tomography

The resolution and effective imaging depth (EID) of spectral domain optical coherence tomography (OCT) are of great importance for visualizing the fine details of biological tissues. To this end, a theoretical model for the micron resolution spectral domain OCT was proposed with both the temporal coherence and the longitudinal spatial coherence considered. Based on the model, the parameters that influence the axial resolution, the signal intensity and the EID can be quantitatively analyzed. Among all the parameters the focusing effect of objective lens affects the signal intensity most due to the fast broadening of the effective point spread function (PSF) incident on the photosensitive surface of detector. It limits the EID defined by the signal fall-off less than 500 mu m. Similar to the dispersion mismatch between the sample arm and the reference arm, the NA of objective lens does influence the axial resolution in the form of convolution. A large NA, such as 0.4, would lead to multiple split peaks and severe side lobes in the axial PSF. The axial resolution could even be reduced to 11.6 mu m, which is about ten times of the micron level resolution. For the EID defined by the micron axial resolution NA < 0.1 should be recommended, otherwise, the method to eliminate the effect of NA must be taken. Finally, the experimental results are presented to demonstrate the accuracy and effectiveness of our model.