Lens-less 3D raster-scanning endomicroscopy via multicore fibers (MCFs) enables minimally invasive applications for instance auto fluorescent imaging for cancer diagnostics in the brain. However, it suffers from various issues: (i) periodic core arrangements, which result in higher diffraction orders and a limited field of view, (ii) bend-sensitive transfer functions which require constant on-line calibration, and (iii) inherent (static) differential path length differences of the individual fiber cores. To overcome these limitations, we present an MCF with 1200 aperiodically arranged cores, which is twisted to decrease dynamic bending sensitivity. Furthermore, diffractive optical elements (DOEs) were directly imprinted on the fiber facet using 2-Photon-Polymerization to compensate the inter-core-dispersion.
As a first demonstration, a simple imaging system consisting only of a camera and an MCF with an integrated DOE for phase compensation and focusing is realized for direct imaging. As a result, a flexible phase preserving fiber waveguide is realized, that can easily be included in standard microscopes to extend their field of applications to deep tissue and in vivo imaging.
Lens-less endoscopy based on multi-core fibers (MCFs) with aperiodic core arrangements enables 3D imaging deep inside tissue with reduced imaging artifacts such as higher-order diffraction. With a scalable iterative stack-and-draw process, we fabricated and characterized (e.g. cross-talk) two aperiodic MCFs: (i) a 250 µm fiber with 420 cores and (ii) a 333 µm fiber with 1281 cores. Since lens-less endoscopy is sensitive to dynamic bending, two different approaches to twist the fibers were evaluated: i) rotation of the fiber preform during fiber drawing and (ii) post-production twisting of the MCF within a fiber processing station.
Lensless endoscopy based on multicore fibres is a promising concept for 3D imaging deep inside tissue. In-depth design studies regarding novel aperiodic multicore fibre designs and their advantages in terms of endoscopy performance are presented.
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