Low-loss single-mode hybrid-lattice hollow-core photonic-crystal fibre

Hollow-core photonic crystal fibres: Low loss with hybrid-lattice cladding A hybrid microstructured cladding significantly reduces confinement loss and preserves single-mode operation in hollow-core photonic crystal fibres. The hybrid cladding was conceptualised and designed by Fetah Benabid of XLIM Institute, CNRS, and colleagues in France and Italy. It is made of an inner cladding of six tubes connected to an outer basket weave-like 'Kagome' lattice via a number of small, thin tubes. Hollow-core photonic crystal fibres surrounded by this hybrid cladding demonstrated a minimum loss figure of 1.6 decibels per kilometre at wavelengths of 1050 nanometres with robust single-mode operation in a ten-metre-long fibre. The design demonstrates the concept's potential for single-mode waveguides and could contribute towards realising the next generation of long-haul optical fibres. Remarkable recent demonstrations of ultra-low-loss inhibited-coupling (IC) hollow-core photonic-crystal fibres (HCPCFs) established them as serious candidates for next-generation long-haul fibre optics systems. A hindrance to this prospect and also to short-haul applications such as micromachining, where stable and high-quality beam delivery is needed, is the difficulty in designing and fabricating an IC-guiding fibre that combines ultra-low loss, truly robust single-modeness, and polarisation-maintaining operation. The design solutions proposed to date require a trade-off between low loss and truly single-modeness. Here, we propose a novel IC-HCPCF for achieving low-loss and effective single-mode operation. The fibre is endowed with a hybrid cladding composed of a Kagome-tubular lattice (HKT). This new concept of a microstructured cladding allows us to significantly reduce the confinement loss and, at the same time, preserve truly robust single-mode operation. Experimental results show an HKT-IC-HCPCF with a minimum loss of 1.6 dB/km at 1050 nm and a higher-order mode extinction ratio as high as 47.0 dB for a 10 m long fibre. The robustness of the fibre single-modeness is tested by moving the fibre and varying the coupling conditions. The design proposed herein opens a new route for the development of HCPCFs that combine robust ultra-low-loss transmission and single-mode beam delivery and provides new insight into IC guidance.

Automated summary

The design of hollow-core photonic crystal fibres with hybrid-lattice cladding significantly reduces confinement loss and preserves single-mode operation, showing potential for next-generation optical fibres.