Miniaturized coded ptychographic microscopy via spherical wave illumination

Coded ptychographic microscopy (CPM) is a lensless imaging technique that captures low-resolution diffraction images at various lateral positions and reconstructs them into high-throughput micrographs. The forward imaging model typically assumes the light source to be a plane wave. While this assumption simplifies calculations, it hinders the miniaturization necessary for maintaining imaging quality. A reduced axial distance from the light source to the sample can cause the plane wave approximation to fail, introducing ambiguities. In this Letter, a compact prototype has been developed, employing an accurate computational method to estimate the spatial position of the light source for the spherical wave model. A translation calibration method was implemented to precisely calculate the object's displacement. During reconstruction, iterative decoupling of the light source and object mitigates image degradation caused by a reduced source-to-sample distance. Simulations and experimental comparisons demonstrate a 25.5% resolution improvement over typical CPM based on plane waves under the same close-range conditions. This approach has the potential to significantly advance the miniaturization of CPM and enhance its applications in digital pathology and cytometric analysis.