Near-field misalignment-robust real-domain Fourier ptychographic microscopy with spherical-wave forward model and micro-LED array illumination

Fourier ptychographic microscopy (FPM) is a computational imaging method that enables high-resolution, large field-of-view quantitative phase imaging of transparent or reflective samples. It conventionally relies on large LED arrays and assumes plane-wave illumination, which constrains system miniaturization and limits performance under near-field illumination conditions. Here, we introduce a compact micro-FPM (μFPM) platform based on near-field illumination from a micro-LED array. It is combined with a new reconstruction framework: a real-domain FPM (rdFPM) algorithm that accurately models spherical wavefront illumination and the improved intensity constraint (IIC) algorithm update procedure, which generally makes any FPM reconstruction robust and stable even in misaligned systems. In the near-field FPM, each micro-LED acts as a localized point source, producing strongly spherical, spatially varying illumination that breaks standard plane-wave FPM models. The proposed rdFPM framework, supported by the designed system-specific calibration method, incorporates spherical wavefront curvature and non-uniform illumination directly into the forward model. Thus, the proposed framework enables robust amplitude and phase reconstruction despite the limited and localized illumination area of individual emitters. Simulations and experimental results using resolution targets target and biological specimens validate the robustness of the proposed μFPM system and rdFPM+IIC reconstruction framework. Results demonstrate high-quality reconstructions of both amplitude and phase objects with 2.5-2.8-fold resolution improvement over the objective diffraction limit, confirming the proposed platform as a compact, alignment-robust, and high-performance alternative to conventional FPM implementations. By uniting on-chip micro-LED illumination with rdFPM+IIC reconstruction and geometry-locked calibration, this work establishes a practical pathway toward true on-chip quantitative Fourier ptychographic microscopy.