Analysis, Simulations, and Experiments for Far-Field Fourier Ptychography Imaging Using Active Coherent Synthetic-Aperture

Mingyang Yang,Hui Zhao,Xuewu Fan,Yuming Wang

doi:10.3390/app12042197

Abstract

Fourier ptychography (FP) is a powerful phase retrieval method that can be used to reconstruct missing high-frequency details and high-space-bandwidth products in microscopy. In this study, we further advanced the application of FP in microscopic imaging to the field of macroscopic far-field imaging, incorporating camera scanning for spatial resolution improvement. First, on the basis of the Fraunhofer diffraction mechanism and the transmission imaging model, we found the analysis of the associated theoretical fundamentals via simulations and experiments to be crucially relevant to the far-field of FP imaging. Second, we built an experimental device with long-distance imaging and experimentally demonstrated the relationship between the spectrum overlap ratio and the reconstructed high-resolution image. The simulation and experimental results showed that an overlap ratio higher than 50% had a good reconstruction effect. Third, camera scanning was used to obtain low-resolution intensity images in this study, for which the scanning range was wide and spherical wave illumination was satisfied, and therefore different positions corresponded to different aberrations of low-resolution intensity images, and even different positions of the same image had aberration differences, leading to inconsistencies in the aberrations of different images. Therefore, in the reconstruction process, we further overcame the effect of the inconsistency of aberrations of different images using the partition reconstruction method, which involves cutting the image into smaller parts for reconstruction. Finally, with the proposed partition reconstruction algorithm, we were able to resolve 40 μm line width of GBA1 resolution object and obtain a spatial resolution gain of 4× with a working distance of 2 m.

Highlights

Fourier ptychography (FP) has emerged as a powerful tool to improve spatial resolution in microscopy [1,2]
We demonstrate a transmissive far-field FP imaging system using camera scanning, which uses a small aperture to synthesize a large aperture and an equivalent aperture expansion to improve the spatial resolution of the system
A total of 225 LR images with resolution of 231pixel × 231 pixel was was obtained with a scanning step of 4.5 mm and a 61% overlap ratio between two adjacent obtained with a scanning step of 4.5 mm and a 61% overlap ratio between two adjacent images

Summary

Introduction

Fourier ptychography (FP) has emerged as a powerful tool to improve spatial resolution in microscopy [1,2]. Zheng et al first proposed the Fourier ptychography microscopy (FPM) imaging technique and successfully built a microscopy setup [1]. In FPM, using light-emitting diodes (LEDs) to illuminate the object at different angles, we can obtain a series of low-resolution (LR) intensity images in the image plane and synthesize them together [1–4]. FP iteratively transforms the LR images in the spatial and frequency domains and minimizes the difference between the measured and calculated images [3–7]. The high-resolution (HR) intensity image and corresponding phase information can be recovered with the synthesized aperture. In the Fourier plane, camera scanning is a commonly used method that can effectively scan different portions of the space with the shifting pupil function [3]

Methods

Results

Discussion

Conclusion