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.
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