Ptychographic lensless coherent endomicroscopy through a flexible fiber bundle.

Conventional fiber-bundle-based endoscopes allow minimally invasive imaging through flexible multi-core fiber (MCF) bundles by placing a miniature lens at the distal tip and using each core as an imaging pixel. In recent years, lensless imaging through MCFs was made possible by correcting the core-to-core phase distortions pre-measured in a calibration procedure. However, temporally varying wavefront distortions, for instance, due to dynamic fiber bending, pose a challenge for such approaches.

Fourier holographic endoscopy for imaging continuously moving objects.

Coherent fiber bundles are widely used for endoscopy, but conventional approaches require distal optics to form an object image and acquire pixelated information owing to the geometry of the fiber cores. Recently, holographic recording of a reflection matrix enables a bare fiber bundle to perform pixelation-free microscopic imaging as well as allows a flexible mode operation, because the random core-to-core phase retardations due to any fiber bending and twisting could be removed in situ from the recorded matrix. Despite its flexibility, the method is not suitable for a moving object because the fiber probe should remain stationary during the matrix recording to avoid the alteration of the phase retardations.

Flexible-type ultrathin holographic endoscope for microscopic imaging of unstained biological tissues.

Ultrathin lensless fibre endoscopes offer minimally invasive investigation, but they mostly operate as a rigid type due to the need for prior calibration of a fibre probe. Furthermore, most implementations work in fluorescence mode rather than label-free imaging mode, making them unsuitable for general medical diagnosis. Herein, we report a fully flexible ultrathin fibre endoscope taking 3D holographic images of unstained tissues with 0.

Single-shot multiple-depth macroscopic imaging by spatial frequency multiplexing.

We present a low-coherence interferometric imaging system designed for 3-dimensional (3-D) imaging of a macroscopic object through a narrow passage. Our system is equipped with a probe-type port composed of a bundle fiber for imaging and a separate multimode optical fiber for illumination. To eliminate the need for mechanical depth scanning, we employ a spatial frequency multiplexing method by installing a 2-D diffraction grating and an echelon in the reference arm.

Removal of back-reflection noise at ultrathin imaging probes by the single-core illumination and wide-field detection.

Thin waveguides such as graded-index lenses and fiber bundles are often used as imaging probes for high-resolution endomicroscopes. However, strong back-reflection from the end surfaces of the probes makes it difficult for them to resolve weak contrast objects, especially in the reflectance-mode imaging. Here we propose a method to spatially isolate illumination pathways from detection channels, and demonstrate wide-field reflectance imaging free from back-reflection noise.