Novel process eases production of hollow-core fiber

The recent developments in hollow-core photonic bandgap fiber technology have made their production easier and cheaper as well as reaching their natural limits. A simple fabrication has been developed in which the capillaries are stacked together and thicker-walled capillaries were used, and the entire structure during fiber drawing was inflated. The inflation helps to close the interstitial air holes that makes it possible to form a core without adding the core tube. The core formed by omitting seven capillaries from the stack is filled at each end using much shorter capillaries that remains unsupported in the middle. A tapered hollow-core fiber has been used to efficiently compress and deliver amplified femtosecond pulses from a mode-locked fiber laser as solitons over several meters of fiber. The transform-limited hollow-core fiber output has been an efficient source for frequency-doubling, resulting in 60% conversion efficiency to the green.