Diagonal illumination scheme for Fourier ptychographic microscopy: resolution doubling and aliasing minimization

Fourier ptychographic microscopy (FPM) is a high-throughput computational imaging technology that enables wide-field and high-resolution imaging of samples with both amplitude and phase information. It holds great promise for quantitative phase imaging (QPI) on a large population of cells in parallel. However, detector undersampling leads to spectrum aliasing, which may significantly degenerate the resolution, efficiency, and quality of QPI, especially when an objective lens with a high space-bandwidth product is used. Here, we introduce a diagonal illumination scheme for FPM to minimize spectrum aliasing, enabling high-resolution QPI under a limited detector sampling rate. By orienting the LED illumination diagonally relative to the detector plane, the non-aliased sampling frequency of the raw image under oblique illumination can be maximized. This illumination scheme, when integrated with a color camera, facilitates single-shot, high-throughput QPI, effectively overcoming spectrum aliasing and achieving incoherent diffraction-limited resolution. Theoretical analysis, simulations, and experiments on resolution target and live cells validate the effectiveness and the proposed illumination scheme, offering a potential guideline for designing an FPM platform for high-speed QPI under the limited detector sampling rates.