Optimal phase-transfer-enabled high-fidelity Fourier ptychographic quantitative phase imaging

Fourier ptychographic quantitative phase imaging (FP-QPI) is a promising label-free microscopy technique that has shown broad applications in biomedicine owing to its large-field and high-resolution imaging features. However, the low-frequency components of the phase spectrum cannot be transferred into detectable intensity variations when the illumination angle is smaller than the maximal acceptance angle of the objective. As a result, phase underestimation occurs, inherently degrading the fidelity of FP-QPI. Here, we present optimal phase-transfer-enabled FP-QPI (OFP-QPI) to address this issue by complementarily combining defocus modulation and angle-varied illumination into each intensity measurement at a single defocus plane. Low-frequency phase-to-intensity transfer from defocus modulation and data redundancy from angle-varied illumination collectively enable full phase spectrum reconstruction, thus providing high-fidelity imaging results. We develop a strategy to determine the optimal phase transfer and demonstrate that OFP-QPI reduces the phase imaging error from 52.2% to 11.3%. Experiments on RHNC cells validate the capability of OFP-QPI to perform large-field and long-term cell observation. These results indicate that OFP-QPI enables high-fidelity quantitative phase imaging over extended time scales, making it well suited for long-term, label-free studies of dynamic cellular processes.