3 - Hollow-core fibers

Abstract

The hollow-core fiber, although not a new arrival in the fiber optics family, is one of the most dynamically developed, and arguably the most fascinating areas of specialty optical fibers. As opposed to the standard single-mode or multimode fibers or most solid-core photonic crystal fiber realizations, where light is guided owing to the total internal reflection mechanism, the hollow-core fibers relay on the photonic bandgap or antiresonance effects to confine and guide light in a hollow core surrounded by various types of microstructured claddings. In particular, the latter group, commonly referred to as the antiresonant fibers, arrived with considerable promises of pushing the attenuation limits below the standard single-mode fiber and low-latency transmission or transmission beyond the confines of silica’s attenuation characteristics. Guidance in the hollow core can also be associated with near-to-negligible chromatic dispersion and nonlinearity, which stirred interest from the ultrafast laser community looking forward to new means of femtosecond laser pulse delivery over fiber. In the following, we focus on some of the less mainstream yet unique and successful applications of antiresonant hollow-core fibers, which involve new mid-infrared gas sensing cells with sensitivity going down to single parts per billion or functionalization of the fibers with fluorescent nanodiamond particles for optical sensing of magnetic fields with nT-level sensitivity. We also discuss means of modification of the fibers’ microstructure for arriving at highly birefringent hollow-core fibers or for providing the short-wavelength, that is, visible and UV–violet transmission along with an environment suitable for the interaction of biological matter with the lightwave by infiltration of the hollow core with liquids.