Symmetrical illumination based extending depth of field in Fourier ptychographic microscopy.

Fourier ptychographic microscopy (FPM), simply replacing the traditional light source of a microscope with a LED array, can obtain high resolution and large field of view images simultaneously. A symmetrical LED illumination FPM is presented to improve the quality of high resolution images for defocus or thick samples in this paper. It is proven theoretically that symmetrical LED illumination had higher defocus tolerance than that of single LED illumination at first. Then, it is confirmed that symmetrical LED illumination FPM has better low-resolution images and reconstruction effect for defocus samples than that of single LED illumination by simulated and experimental results. Compared with the single illumination FPM, it is demonstrated that the depth of field of symmetrical FPM is more than doubled.