Widefield lensless imaging through a fiber bundle via speckle correlations

Abstract

Flexible fiber-optic endoscopes provide a solution for imaging at depths beyond the reach of conventional microscopes. Current endoscopes require focusing and/or scanning mechanisms at the distal end, which limit miniaturization, frame-rate, and field of view. Alternative wavefront-shaping based lensless solutions are extremely sensitive to fiber-bending. We present a lensless, bend-insensitive, single-shot imaging approach based on speckle-correlations in fiber bundles that does not require wavefront shaping. Our approach computationally retrieves the target image by analyzing a single camera frame, exploiting phase information that is inherently preserved in propagation through convnetional fiber bundles. Unlike conventional fiber-based imaging, planar objects can be imaged at variable working distances, the resulting image is unpixelated and diffraction-limited, and miniaturization is limited only by the fiber diameter.

Two-photon lensless micro-endoscopy with in-situ wavefront correction

“…The measured transverse (x-y) focal spot size was measured to have a FWHM of 5.4µm ± 0.2 ( Fig.4(b)). A value which is in accordance with the measured axial resolution, and also the expected diffraction-limited spot size dictated by the measurement geometry [18]:…”

“…These are expected to yield an optimization time of the order of seconds or less even using fluorescent markers, as was recently demonstrated using galvanometric-mirrors for 2PF microscopy through scattering tissue [30]. In general, any similar approaches for wavefront correction using nonlinear feedback that were originally developed for scattering media are directly applicable for bundle-based endoscopy, since a fiber bundle can be considered as a thin scattering layer [18]. After the initial focusing, image acquisition speed is limited by the galvanometric scanners speed.…”

“…The field of view using fiber bundles with ordered cores is limited by the diffraction side-lobes of the periodic arrangement of cores [18], and the fiber 'memory-effect' angular range. The maximal angular FoV will be attained by using a disordered bundle having single-mode fibers, with no light propagation between the cores.…”

Ultrathin endoscopes based on multicore fibers and adaptive optics: a status review and perspectives

“…64 More recently, speckle-based imaging has also been reported. 65,66 Imaging fiber bundles are often fabricated with very small Λ, down to 5 μm, which comes at the cost of increased cross talk between the cores and eliminates many of the advantages of MCF, cf., Sec. 2, but can often be tolerated in incoherent imaging.…”

Deep learning enabled real time speckle recognition and hyperspectral imaging using a multimode fiber array

“…Compared to traditional approaches such as Integral Field Spectrometers [18,19], complex media can offer new opportunities for combining broadband transmission with high spectral resolution [20,21,22]. In the spatial domain, multimode fibers as well as multi-core fiber bundles are a topic of study for a variety of imaging applications such as remote sensing and endoscopy [23,24,25,26].…”