Complex-domain-enhancing neural network for large-scale coherent imaging

Large-scale computational imaging can provide remarkable space-bandwidth product that is beyond the limit of optical systems.In coherent imaging(CI),the joint reconstruction of amplitude and phase further expands the information throughput and sheds light on label-free observation of biological samples at micro-or even nano-levels.The existing large-scale CI techniques usually require scanning/modulation multiple times to guarantee measurement diversity and long exposure time to achieve a high signal-to-noise ratio.Such cumbersome procedures restrict clinical applications for rapid and lowphototoxicity cell imaging.In this work,a complex-domain-enhancing neural network for large-scale CI termed CI-CDNet is proposed for various large-scale CI modalities with satisfactory reconstruction quality and efficiency.CI-CDNet is able to exploit the latent coupling information between amplitude and phase(such as their same features),realizing multidimensional representations of the complex wavefront.The cross-field characterization framework empowers strong generalization and robustness for various coherent modalities,allowing high-quality and efficient imaging under extremely low exposure time and few data volume.We apply CI-CDNet in various large-scale CI modalities including Kramers–Kronigrelations holography,Fourier ptychographic microscopy,and lensless coded ptychography.A series of simulations and experiments validate that CI-CDNet can reduce exposure time and data volume by more than 1 order of magnitude.We further demonstrate that the high-quality reconstruction of CI-CDNet benefits the subsequent high-level semantic analysis.

Non-iterative complex wave-field reconstructionbased on Kramers–Kronig relations

A non-iterative and non-interferometric computational imaging method to reconstruct a complex wave field called synthetic aperture imaging based on Kramers–Kronig relations(KKSAI)is reported.By collecting images through a modified microscope system with pupil modulation capability,we show that the phase and amplitude profile of the sample at pupil limited resolution can be extracted from as few as two intensity images by using Kramers–Kronig(KK)relations.It is established that as long as each subaperture’s edge crosses the pupil center,the collected raw images are mathematically analogous to off-axis holograms.This in turn allows us to adapt a recently reported KK-relations-based phase recovery framework in off-axis holography for use in KKSAI.KKSAI is non-iterative,free of parameter tuning,and applicable to a wider range of samples.Simulation and experiment results have proved that it has much lower computational burden and achieves the best reconstruction quality when compared with two existing phase imaging methods.

Ptycho-endoscopy on a lensless ultrathin fiber bundle tip

Synthetic aperture radar(SAR)utilizes an aircraft-carried antenna to emit electromagnetic pulses and detect the returning echoes.As the aircraft travels across a designated area,it synthesizes a large virtual aperture to improve image resolution.Inspired by SAR,we introduce synthetic aperture ptycho-endoscopy(SAPE)for micro-endoscopic imaging beyond the diffraction limit.SAPE operates by hand-holding a lensless fiber bundle tip to record coherent diffraction patterns from specimens.The fiber cores at the distal tip modulate the diffracted wavefield within a confined area,emulating the role of the‘airborne antenna’in SAR.The handheld operation introduces positional shifts to the tip,analogous to the aircraft’s movement.These shifts facilitate the acquisition of a ptychogram and synthesize a large virtual aperture extending beyond the bundle’s physical limit.We mitigate the influences of hand motion and fiber bending through a low-rank spatiotemporal decomposition of the bundle’s modulation profile.Our tests demonstrate the ability to resolve a 548-nm linewidth on a resolution target.The achieved space-bandwidth product is~1.1 million effective pixels,representing a 36-fold increase compared to that of the original fiber bundle.Furthermore,SAPE’s refocusing capability enables imaging over an extended depth of field exceeding 2 cm.The aperture synthesizing process in SAPE surpasses the diffraction limit set by the probe’s maximum collection angle,opening new opportunities for both fiber-based and distal-chip endoscopy in applications such as medical diagnostics and industrial inspection.