Spatially‐Coded Fourier Ptychography: Flexible and Detachable Coded Thin Films for Quantitative Phase Imaging with Uniform Phase Transfer Characteristics

Abstract

Fourier ptychography (FP) is an enabling imaging technique that produces high‐resolution complex‐valued images with extended field coverages. However, when FP images a phase object with any specific spatial frequency, the captured images contain only constant values, rendering the recovery of the corresponding linear phase ramp impossible. This challenge is not unique to FP but also affects other common microscopy techniques — a rather counterintuitive outcome given their widespread use in phase imaging. The underlying issue originates from the non‐uniform phase transfer characteristic inherent in microscope systems, which impedes the conversion of object wavefields into discernible intensity variations. To address this challenge, spatially‐coded Fourier ptychography (scFP) is presented for true quantitative phase imaging. In scFP, a flexible and detachable coded thin film is attached atop the image sensor in a regular FP setup. The spatial modulation of this thin film ensures a uniform phase response across the entire synthetic bandwidth. It improves reconstruction quality, corrects refractive index underestimation issues prevalent in conventional FP, and adds a new dimension of measurement diversity in spatial domain. The development of scFP is expected to catalyze new research directions and applications for phase imaging, emphasizing the need for true quantitative accuracy with uniform frequency response.

Ptycho-endoscopy on a lensless ultrathin fiber bundle tip

“…As Eq. ( 3 ) suggests, an alternative implementation of SAPE is to replace the small lens of the miniaturized camera with a coded surface directly attached on top of the coverglass of the image sensor 18 . The coded surface serves the role of in Eq.…”

“…Alternatively, SAPE can be implemented in an existing distal-chip endoscope with a miniaturized camera. The small lens element of the miniaturized camera is then replaced with a coded surface 18 that serves the role of the fiber bundle for light wave modulation. In this case, the intentional defocusing distance corresponds to the space between the coded surface and the pixel array of the image sensor.…”

“…Notably, the SAPE concept can also be extended to distal-chip endoscopy, where a miniaturized camera is directly placed at the distal end of the endoscope probe 16 , 17 . To implement SAPE in this setting, the small lens element of the miniaturized camera can be replaced by a thin coded layer on the sensor 18 , which modulates the diffracted wavefields like the fiber bundle tip.…”