Fabrication of Shatter-Proof Metal Hollow-Core Optical Fibers for Endoscopic Mid-Infrared Laser Applications

Katsumasa Iwai,Mitsunobu Miyagi,Yi-Wei Shi,Yuji Matsuura,Hiroyuki Takaku

doi:10.3390/fib6020024

Abstract

A method for fabricating robust and thin hollow-core optical fibers that carry mid-infrared light is proposed for use in endoscopic laser applications. The fiber is made of stainless steel tubing, eliminating the risk of scattering small glass fragments inside the body if the fiber breaks. To reduce the inner surface roughness of the tubing, a polymer base layer is formed prior to depositing silver and optical-polymer layers that confine light inside the hollow core. The surface roughness is greatly decreased by re-coating thin polymer base layers. Because of this smooth base layer surface, a uniform optical-polymer film can be formed around the core. As a result, clear interference peaks are observed in both the visible and mid-infrared regions. Transmission losses were also low for the carbon dioxide laser used for medical treatments as well as the visible laser diode used for an aiming beam. Measurements of bending losses for these lasers demonstrate the feasibility of the designed fiber for endoscopic applications.

Highlights

Mid-infrared lasers are increasingly being used in medical applications because mid-infrared light is strongly absorbed by the water, proteins, and lipids in human tissue
The RMS roughness of the inner surface of the original SUS tube was as large as 0.6–0.9 μm, and it was made drastically smoother by the base coat
One can see that the inner surface of the SUS tubing was smoothed by applying the resin base coating

Summary

Introduction

Mid-infrared lasers are increasingly being used in medical applications because mid-infrared light is strongly absorbed by the water, proteins, and lipids in human tissue. Mid-infrared lasers can be used in combination with a flexible endoscope or catheter for minimally invasive treatments of tumors and other diseased tissue. Such applications require an optical fiber that is sufficiently thin and flexible for insertion into the working channel of endoscopes or thin catheters. Common silica-glass fibers cannot transmit mid-infrared light with wavelengths longer than 2 μm because of absorption in the silica-glass material [1], so many types of infrared optical fibers have been developed, such as chalcogenide-glass fibers [2,3], metal-halide polycrystalline fibers [4,5], and hollow-core optical fibers [6,7]. The other is made entirely of glass and utilizes photonic crystal structures to confine light in the central air core [11,12]

Methods

Results

Conclusion