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Low-loss hollow-core silica/air photonic bandgap fibre


Photonic bandgap structures use the principle of interference to reflect radiation. Reflection from photonic bandgap structures has been demonstrated in one, two and three dimensions and various applications have been proposed1,2,3,4. Early work in hollow-core photonic bandgap fibre technology5 used a hexagonal structure surrounding the air core; this fibre was the first demonstration of light guided inside an air core of a photonic bandgap fibre. The potential benefits of guiding light in air derive from lower Rayleigh scattering, lower nonlinearity and lower transmission loss compared to conventional waveguides. In addition, these fibres offer a new platform for studying nonlinear optics in gases6. Owing largely to challenges in fabrication, the early air-core fibres were only available in short lengths, and so systematic studies of loss were not possible. More recently, longer lengths of fibre have become available7,8 with reported losses of 1,000 dB km-1. We report here the fabrication and characterization of long lengths of low attenuation photonic bandgap fibre. Attenuation of less than 30 dB km-1 over a wide transmission window is observed with minimum loss of 13 dB km-1 at 1,500 nm, measured on 100 m of fibre. Coupling between surface and core modes of the structure is identified as an important contributor to transmission loss in hollow-core photonic bandgap fibres.

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Figure 1: SEM image of air-core PBGF profile, truncated to show central core defect and first rings of holes of microstructured cladding.
Figure 2: Comparison of experimental and theoretical mode profiles for the air-core PBGF.
Figure 3: Transmission spectra for the full 100-m-long fibre and two 1.5-m-long pieces taken from the end and the beginning of the 100-m section.
Figure 4: Optical attenuation as a function of wavelength for the 100-m-long air-core PBGF. A cutback method using a commercial Photon-Kinetics measurement bench was used.
Figure 5: Calculated dispersion of air-core modes and bandgap modes for the fibre profile in Fig. 1.


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Correspondence to Karl W. Koch.

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Smith, C., Venkataraman, N., Gallagher, M. et al. Low-loss hollow-core silica/air photonic bandgap fibre. Nature 424, 657–659 (2003).

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