Hollow core large mode area fibre employing a subwavelength grating reflector

Abstract

Hollow core large mode area fibres are ideal candidates to guide light at high powers while avoiding non-linear effects and, as such, they are generating much scientific interest. A variety of fibres have been investigated, including tube lattice photonic bandgap fibres and Kagomé-latticed photonic crystal fibres. One of the major challenges in obtaining low loss hollow core fibres is related to the unavoidable perturbations induced by the coupling between the core and cladding modes which is responsible for the increase of leakage loss. Recent approach based on the insertion of additional antiresonant elements demonstrates the significance of fibre geometrical parameters and shows leakage loss of an order of ~10-4 dB/m. In this paper, we present preliminary results of a novel approach to fibres that guide light in a large hollow core, starting from the high index contrast grating reflector platform. Subwavelength gratings have been used to achieve broadband mirrors with reflectivity greater than 99%. Importantly, the physical dimensions of the grating must be smaller than the wavelength of incident light, which implies that the diffraction order of interest is 0th. Under a surface normal incidence on diffraction grating, evanescent orders in the direction parallel to the grating period overlap with the leaky mode of the grating leading to the effect of guided mode resonance and a destructive interference effect between the two grating modes, which results in high reflection