Abstract
We report the fabrication and characterization of the first double clad tubular anti-resonant hollow core fiber. It allows to deliver ultrashort pulses without temporal nor spectral distortions in the 700-1000 nm wavelength range and to efficiently collect scattered light in a high numerical aperture double clad. The output fiber mode is shaped with a silica microsphere generating a photonic nanojet, making it well suitable for nonlinear microendoscopy application. Additionally, we provide an open access software allowing to find optimal drawing parameters for the fabrication of tubular hollow core fibers.
Highlights
A major issue in early cancer diagnostic is the identification of potential tumors that requires the careful preparation and inspection of ex vivo tissue biopsies by standard histology (haematoxylin, eosin and saffron (HES) staining)
For coherent anti-Stokes Raman scattering (CARS) imaging, an additional short pulse has to be synchronized to match the vibrational frequency of the molecule to be probed [10] and it is convenient to use continuously tunable optical parametric oscillators (OPOs) delivering both pulses [11]
Starting from a 29 μm mode field diameter (MFD) at the fiber output would require a ×30-×60 de-magnification to reach a near diffraction limited spot, which would require large focal length lenses, a solution unpractical regarding the final compactness on the endoscope distal head
Summary
A major issue in early cancer diagnostic is the identification of potential tumors that requires the careful preparation and inspection of ex vivo tissue biopsies by standard histology (haematoxylin, eosin and saffron (HES) staining). Collection efficiency, in the visible spectral range (typically between 400 and 650 nm, depending on the imaging modality), and to guide them back to the various detection channels (PMTs) This signal collection is optimally achieved by using a high numerical aperture (NA) double cladding surrounding the fiber core [1,2,3,4,6,8]. A double clad can be located much closer to the main core, and its surface can be enhanced while keeping an outer diameter sufficiently small for a flexible fiber Such fibers were successfully used to deliver ultrashort pulses in the context of nonlinear fiber-based microscopy [14,22,23], but the lack of double clad prevented them to be used in an endoscopic configuration. The fiber has been functionalized to transform the original output fundamental mode with a large mode field diameter (MFD) and low NA into a near diffraction limited spot, making it compatible with miniature distal imaging probes [6,24]
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