We present an endoscopic system allowing to perform 3-photon excitation fluorescence and third harmonic generation imaging. The ultrashort pulses required for multiphoton excitation are delivered from an ultrafast laser system to the endoscopic probe using a connectorized hollow core delivery fiber.
The lensless endoscope represents the ultimate limit in miniaturization of imaging tools: an image can be transmitted through an optical fiber by numerical or physical inversion of the fiber's pre- measured transmission matrix. We present here a novel fiber-optic component, a "tapered multi-core fiber (MCF)", designed for integration into ultra-miniaturized endoscopes for minimally invasive two-photon point-scanning imaging. This new design addresses the power delivery issue that has faced MCF based lensless endoscopes. We achieve experimentally a factor 6.0 increase in two-photon signal yield while keeping the ability to point-scan by the memory effect. We report two-photon fluorescent imaging of cells and neurons with these improved MCF tapered fibers.
We demonstrate a highly multimodal nonlinear micro-endoscope for real-time, label-free imaging of biological tissues. The endoscope can perform two and three photon excited fluorescence, second, third harmonic and CARS imaging for different excitation wavelengths. Ultrashort pulses are delivered to the sample by a double-clad antiresonant hollow core fiber over the 800-1800 nm spectral band. The fiber tip is placed into a doubly resonant piezoelectric tube which allows a spiral scanning on the sample. The endoscope distal head containing the scanning device and the GRIN micro-objective is 1.5 mm in diameter and 35 mm long. Real-time nonlinear imaging at 10 frame/s is demonstrated.
We experimentally demonstrate a novel approach to generate a multi-frequency comb light source with a high mutual coherence in an all-fiber system. Starting from EOM combs, we exploit spatial light multiplexing in a 3-core all-normal nonlinear silica fiber at 1550 nm. Each pulse propagates in its own core to experience a nonlinear broadening but within the same fiber. We obtained 3 almost similar output flat-top spectra spanning over 14 nm with 3 nJ per pulse at 250 MHz and a flat phase noise spectrum down to -125 dBc/Hz. The signal-to-noise ratio of interferograms is about 40 dB.
We demonstrate 3-photon fluorescence micro-endoscopy using a negative curvature hollow core fiber and a 2.2 mm miniature scanning head. The fiber design allows distortion-less, delivery of <100 fs pulses without dispersion pre-compensation requirements. The fiber also features a double cladding allowing the back-collection of nonlinear signals through the same fiber. Sub-micron spatial resolution together with large field of view is made possible by the combination of a miniature distal objective lens with a functionnalization of the fiber output with a GRIN fiber spliced to the output facet. 3-photon fluoresence imaging is demonstrated on various biological samples.
Hybrid optical fibers, i.e. optical fibers that combine, in the same structure, glass with crystal, metal, polymer or a second type of glass, open access to a wide range of optical properties or optical functions not accessible to common single-glass-made optical fibers. Silicon-core fibers are one type of hybrid fibers that have been intensively studied since 2006 with the aim to take benefit of the mid-infrared transparency of silicon or to implement opto-electrical functions in the optical fiber itself. Some of the unique optical properties of these semiconductor-core fibers have been demonstrated but it is admitted that optical losses are still today a drag on the rise of performances and hence devote specific attention. Post-processing based on laser or thermal annealing can be applied on the as-drawn fibers to improve core crystallinity and then reduce optical losses. However, such processing techniques have been demonstrated on centimeter-long fibers only. In the present paper, we demonstrate as-drawn silicon-core fiber with loss level below 0.2 dB/cm on the 1250-1650nm wavelength range, this fiber being continuously manufactured over length exceeding one hundred of meters. Several fibers have been fabricated from a rod-in-stack approach and different core dimensions ranging from about 0.8 to 3.4 μm have been successively realized and extensive characterizations (XRD, micro-Raman spectroscopy, TEM and ToF-SIMS analysis) have been conducted on the 3.4 μm core fiber. The crystalline state of the core, the absence of oxygen contamination and the optical transmission from 1.1 to 4 μm will be presented.
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