Since their inception, about 20 years ago, hollow-core photonic crystal fiber and its gas-filled form are now establishing themselves both as a platform in advancing our knowledge on how light is confined and guided in microstructured dielectric optical waveguides, and a remarkable enabler in a large and diverse range of fields. The latter spans from nonlinear and coherent optics, atom optics and laser metrology, quantum information to high optical field physics and plasma physics. Here, we give a historical account of the major seminal works, we review the physics principles underlying the different optical guidance mechanisms that have emerged and how they have been used as design tools to set the current state-of-the-art in the transmission performance of such fibers. In a second part of this review, we give a nonexhaustive, yet representative, list of the different applications where gas-filled hollow-core photonic crystal fiber played a transformative role, and how the achieved results are leading to the emergence of a new field, which could be coined “Gas photonics”. We particularly stress on the synergetic interplay between glass, gas, and light in founding this new fiber science and technology.

We report on the first deep-ultraviolet/ultraviolet (DUV/UV) emission using a highly compact microwave-driven plasma-core photonic crystal fiber. The latter consists of a few centimeter long micro-plasma column of a gas mixture in the core of Kagome hollow-core photonic crystal fiber. The plasma is generated by nonintrusively exciting a ternary gas mixture of argon, nitrogen, and oxygen ($\mathrm{Ar}/{\mathrm{N}}_2/{\mathrm{O}}_2$) with a microwave resonator. Several spectral lines in the wavelength range of 200–450 nm were produced, guided by an $\mathrm{Ar}\text{-}{\mathrm{N}}_2\text{-}{\mathrm{O}}_2$ plasma-filled fiber, and controlled by simply varying the gas ratio of this gas mixture. An optimum gas mixture ratio was experimentally and theoretically identified for the strongest emission in the DUV range of 200–275 nm. The developed DUV emitting plasma-core fiber represents an important milestone towards the development of tunable and miniaturized DUV/UV laser sources.