Single multimode fiber endoscope.

Antonio M Caravaca-Aguirre,Rafael Piestun

doi:10.1364/oe.25.001656

Abstract

Multimode fibers can guide thousands of modes capable of delivering spatial information. Unfortunately, mode dispersion and coupling have so far prevented their use in endoscopic applications. To address this long-lasting challenge, we present a robust scanning fluorescence endoscope. A spatial light modulator shapes the input excitation wavefront to focus light on the distal tip of the fiber and to rapidly scan the focus over the region of interest. A detector array collects the fluorescence emission propagated back from the sample to the proximal tip of the fiber. We demonstrate that proper selection of the multimode fiber is critical for a robust calibration and for high signal-to-background ratio performance. We compare different types of multimode fibers and experimentally show that a focus created through a graded-index fiber can withstand a few millimeters of fiber distal tip translation. The resulting scanning endoscopic microscope images fluorescent samples over a field of view of 80µm with a resolution of 2µm.

Highlights

Endoscopic imaging is typically based on single mode fiber bundles, GRIN lenses or hybrid systems of fiber optics and mechanical actuators [1]
A further different method measures and stores each speckle field created at the proximal tip of a multimode fiber (MMF) for various input fields at the distal tip, enabling the reconstruction of the brightness of an object placed at the distal tip [6]
We experimentally demonstrated the feasibility of converting a single MMF into a fluorescence scanning endoscope

Summary

Introduction

Endoscopic imaging is typically based on single mode fiber bundles, GRIN lenses or hybrid systems of fiber optics and mechanical actuators [1]. Papadopoulos et al [3] use digital optical phase conjugation to calibrate a MMF and create a focus in every point at the tip of the fiber, converting the MMF into a scanning fluorescence microscope. Their method is capable of imaging in-vitro neurons with 1-3μm lateral resolution. A further different method measures and stores each speckle field created at the proximal tip of a MMF for various input fields at the distal tip, enabling the reconstruction of the brightness of an object placed at the distal tip [6] None of these techniques has so far overcome the problems arising from fiber perturbations (e.g. shape changes, temperature) that produce mode coupling. We discuss the implications of this work for the advancement of microendoscopy

Principle of operation

Speckle intensity contrast and enhancement

Fluorescence microscopy

Discussion and conclusions