Hollow Optical Fibers for Delivery of CO₂ Laser Light

Abstract

Hollow optical fibers have a tube structure in contrast to common glass-optical fibers made of glass wire and light propagates in the hollow core. Therefore, the hollow optical fiber can transmit mid-infrared light including CO₂ laser light that cannot be delivered by common glass fibers because of the glass absorption. Hollow optical fibers are usually based on glass capillary and a metal film and a polymer film that is transparent in the mid-infrared are formed on the inside of the capillary. The polymer film enhances reflection at a targeted wavelength region by optical interference effect and this reduces the transmission loss of the fiber. A common silver plating is usually used for metal film deposition and a polymer solution is injected into the capillary and dried to from a polymer film. Fabricated hollow optical fibers for CO₂ laser light with an inner diameter of 0.7 mm and a length of 1 m show transmission higher than 90% when the fiber is straight. When bending the fiber, although the transmission is lowered, the fiber keeps transmission high enough for clinical applications.