Tapered Multicore Fiber for Lensless Endoscopes

We present a novel fiber-optic component, a "tapered multicore fiber (MCF)", designed for integration into ultraminiaturized endoscopes for minimally invasive two-photon point-scanning imaging and to address the power delivery issue that has faced MCF-based lensless endoscopes. With it we achieve experimentally a factor 6.0 increase in two-photon signal yield while keeping the ability to point-scan by the memory effect and a factor 8.9 sacrificing the memory effect. To reach this optimal design, we first develop and validate a fast numerical model capable of predicting the essential properties of an arbitrarily tapered MCF from its structural parameters. We then use this model to identify the tapered MCF design parameters that result in a chosen set of target properties (point-spread function, delivered power, presence or absence of memory effect). We fabricate the identified target designs by stack-and-draw and postprocessing on a CO2 laser-based glass processing and splicing system. Finally, we demonstrate the performance gain of the fabricated tapered MCFs in two-photon imaging when used in a lensless endoscope system. Our results show that tailoring of the taper profile brings new degrees of freedom that can be efficiently exploited for lensless endoscopes.