Countering the optical network ‘capacity crunch’ calls for a radical development in optical fibres that could simultaneously minimize nonlinearity penalties, chromatic dispersion and maximize signal launch power. Hollow-core fibres (HCF) can break the nonlinear Shannon limit of solid-core fibre and fulfil all above requirements, but its optical performance need to be significantly upgraded before they can be considered for high-capacity telecommunication systems. Here, we report a new HCF with conjoined-tubes in the cladding and a negative-curvature core shape. It exhibits a minimum transmission loss of 2 dB km−1 at 1512 nm and a <16 dB km−1 bandwidth spanning across the O, E, S, C, L telecom bands (1302–1637 nm). The debut of this conjoined-tube HCF, with combined merits of ultralow loss, broad bandwidth, low bending loss, high mode quality and simple structure heralds a new opportunity to fully unleash the potential of HCF in telecommunication applications.

Laser spectroscopy outperforms electrochemical and semiconductor gas sensors in selectivity and environmental survivability. However, the performance of the state-of-the-art laser sensors is still insufficient for many high precision applications. Here, we report mode-phasedifference photothermal spectroscopy with a dual-mode anti-resonant hollow-core optical fiber and demonstrate all-fiber gas (acetylene) detection down to ppt (parts-per-trillion) and <1% instability over a period of 3 hours. An anti-resonant hollow-core fiber could be designed to transmit light signals over a broad wavelength range from visible to infrared, covering molecular absorption lines of many important gases. This would enable multi-component gas detection with a single sensing element and pave the way for ultra-precision gas sensing for medical, environmental and industrial applications.

We report on a hollow-core fiber (HCF) whose fundamental transmission band covers almost the whole visible spectral window, starting at 440 nm. This HCF, in the form of a nodeless structure (NL-HCF), exhibits unprecedented optical performance in terms of low transmission attenuation of 80 dB/km at 532 nm, a broad transmission bandwidth from 440 to 1200 nm, a low bending loss of 0.2 dB/m at 532 nm under 8 cm bending radius, and single-mode profile. When launched to high-power picosecond laser systems at 532 nm, the fiber, exposed to ambient air, could easily deliver an 80 ps, 58 MHz, 32 W average power laser pulse with no damage and a 20 ps, 1 kHz high-energy laser pulse with a damage threshold in excess of 144 μJ at a fiber output. A proof-of-concept experiment on Raman spectroscopy in ambient air shows the significance of this broadband visible guiding HCF for interdisciplinary applications in nonlinear optics, ultrafast optics, lasers, spectroscopy, biophotonics, material processing, etc.

We demonstrate a 2.8 μm gas Raman laser in a methane-filled hollow-core negative-curvature fiber with average power of 113 mW, pulse energy of 113 μJ and estimated peak power of 9.5 MW. Raman quantum efficiency of 40% has been reached from the pump source at 1.064 μm to the 2nd order vibrational Stokes at 2.812 μm using 1.8 MPa methane gas. To our knowledge, this is the first high peak power fiber-based gas Raman laser in mid-infrared region and a range of applications in supercontinuum generation, laser surgery, molecular tracing and gas detection are in prospect.