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.