Semi-random multicore fibre design for adaptive multiphoton endoscopy.

Youngchan Kim,Chris Dunsby,James Clegg,Jonathan Knight,Mark Neil,Paul French,James Stone,Fernando Favero,Carl Paterson,Sean Warren

doi:10.1364/oe.26.003661

Abstract

This paper reports the development, modelling and application of a semi-random multicore fibre (MCF) design for adaptive multiphoton endoscopy. The MCF was constructed from 55 sub-units, each comprising 7 single mode cores, in a hexagonally close-packed lattice where each sub-unit had a random angular orientation. The resulting fibre had 385 single mode cores and was double-clad for proximal detection of multiphoton excited fluorescence. The random orientation of each sub-unit in the fibre reduces the symmetry of the positions of the cores in the MCF, reducing the intensity of higher diffracted orders away from the central focal spot formed at the distal tip of the fibre and increasing the maximum size of object that can be imaged. The performance of the MCF was demonstrated by imaging fluorescently labelled beads with both distal and proximal fluorescence detection and pollen grains with distal fluorescence detection. We estimate that the number of independent resolution elements in the final image - measured as the half-maximum area of the two-photon point spread function divided by the area imaged - to be ~3200.

Highlights

The use of endoscopy to perform optical imaging in remote spaces is an established technique and there is continued interest to develop thinner endoscopes enabling access to smaller and more confined locations
In this paper we have extended the approach of Sivankutty et al [9], who presented a semirandom multicore optical fibres (MCF) fibre constructed from a hexagonally close-packed array of fibres where the core of each individual fibre was off-centre within its cladding and was incorporated into the bundle with a random rotation
Our work demonstrated an MCF constructed from sub-units consisting of seven single mode cores in a hexagonal close-packed array

Summary

Introduction

The use of endoscopy to perform optical imaging in remote spaces is an established technique and there is continued interest to develop thinner endoscopes enabling access to smaller and more confined locations. One approach to this has been to utilise adaptive optics approaches in combination with optical fibres with multiple single (or few) mode cores [1] or a single multimode optical fibre [2] to perform scanning-spot imaging without the need for a distal lens or scanner. Modal dispersion in multimode fibre makes it challenging to transmit the ultrashort pulses required for multiphoton excitation, since the coherence length of the pulses is typically smaller than the spread in optical path lengths between modes, this is possible by restricting the modes used to a small subset with similar optical path lengths [4]

Methods

Results

Discussion

Conclusion