Tapered multi-core fiber for lensless endoscopes

TL;DR

This paper introduces a tapered multi-core fiber for lensless endoscopes, significantly enhancing two-photon imaging signal strength and enabling customizable optical properties through a validated numerical model and precise fabrication.

Contribution

The study develops a fast predictive model for tapered MCFs, identifies optimal design parameters, and demonstrates improved imaging performance in a lensless endoscope system.

Findings

Achieved a 6.0x increase in two-photon signal yield.

Achieved an 8.9x increase with reduced memory effect.

Validated the design through fabrication and experimental imaging tests.

Abstract

We present 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 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 post-processing on a CO$_{2}$ 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.