Gas-filled microstructured hollow-core fibers (MS-HCFs) have demonstrated many advantages as a minimized gas cell and shown the promising potential of reforming the bulky gas laser and sensors into a more compact and robust all-fiber configuration. The gas–light interaction along MS-HCF could be possibly enhanced by times stronger than that in the Rayleigh zone of the free-space laser beam. In MS-HCF, both the gas and light field could be tightly confined in a core region of tens of area. Meanwhile, its effective interaction length depending on the fiber loss is much extended to tens of meters. The latest development of anti-resonant hollow-core fiber (AR-HCF) demonstrated 0.22 dB/km minimum fiber loss that implies more than a thousand effective length to use.