Hollow core photonic bandgap optical fibres and methods of fabrication
A hollow core photonic bandgap optical fibre comprises: a cladding comprising capillaries in a hexagonal array and a hollow core formed by excluding a hexagonal group of nineteen capillaries from the centre of the hexagonal array. The core is inflated. A core size ratio is 1.26 or above, defined as a ratio of the core diameter to the cladding diameter normalized to the ratio of the core diameter to the cladding diameter in an undistorted hexagonal array; a first ring ratio is between 0.55 and 2.50, defined as a ratio of the length of radially aligned struts separating the capillaries of the first ring to the length of a strut in an undistorted hexagonal array; and a core node spacing is between 0.60 and 1.90, where defined as a ratio of a strut length around the core of a largest corner capillary and a strut length around the core of a smallest side capillary. The fabrication method comprises four different pressures for the core, corner capillary, side capillary and cladding.
1. A hollow core photonic bandgap optical fibre comprising:
a cladding comprising capillaries in a hexagonal array, the capillaries separated from each other by struts connected at nodes, the cladding having a cladding diameter; and
a hollow core formed by excluding a hexagonal group of nineteen capillaries from the centre of the hexagonal array, the core having a core diameter; wherein
the core is bounded by a first ring of capillaries comprising corner capillaries disposed adjacent to corners of the excluded group and side capillaries positioned between the corner capillaries;
and the hexagonal array has dimensions such that:
a core size ratio is between 1.34 and 1.82 inclusive;
where the core size ratio is defined as a ratio of the core diameter to the cladding diameter normalised to the ratio of the core diameter to the cladding diameter in an optical fibre formed from the same number and arrangement of capillaries in an undistorted hexagonal array;
a first ring ratio is between 0.65 and 2.20 inclusive;
where the first ring ratio is defined as a ratio of the length of radially aligned struts separating the capillaries of the first ring to the length of a strut in an undistorted hexagonal array with a core size ratio of 1; and
a core node spacing is between 0.60 and 1.90 inclusive;
where the code node spacing is defined as a ratio of a strut length around the core of a largest corner capillary and a strut length around the core of a smallest side capillary.
2. A hollow core photonic bandgap optical fibre according to claim 1 , in which the optical transmission loss is 1.1 dB/km or less for a wavelength of 1550 nm.
3. A hollow core photonic bandgap optical fibre according to claim 1 , in which the core size ratio is between 1.44 and 1.74 inclusive and the first ring ratio is between about 0.75 and 2.00 inclusive.
4. A hollow core photonic bandgap optical fibre according to claim 3 , in which the optical transmission loss is 1.0 dB/km or less for a wavelength of 1550 nm.
5. A hollow core photonic bandgap optical fibre according to claim 1 , in which the optical transmission loss is 1.2 dB/km or less for a wavelength of 2000 nm.
6. A hollow core photonic bandgap optical fibre according to claim 5 , in which the core size ratio does not exceed 1.80.
7. A hollow core photonic bandgap optical fibre according to claim 5 , in which the core size ratio is between 1.45 and 1.75 inclusive, the first ring ratio is between about 0.70 and 1.50 inclusive, and the core node spacing is between 0.80 and 1.50 inclusive.
8. A hollow core photonic bandgap optical fibre according to claim 7 , in which the optical transmission loss is 1.0 dB/km or less for a wavelength of 2000 nm.
9. A hollow core photonic bandgap optical fibre according to claim 5 , in which the core size ratio is 1.65, the first ring ratio is 1.22, and the core node spacing is 1.20.
10. A hollow core photonic bandgap optical fibre according to claim 9 , in which the optical transmission loss is 0.88 dB/km for a wavelength of 2000 nm.
11. A hollow core photonic bandgap optical fibre according to claim 1 , in which the cladding comprises at least five concentric rings of capillaries around the core.
12. A hollow core photonic bandgap optical fibre according to claim 11 , in which the cladding comprises five, six, seven or eight concentric rings of capillaries around the core.
13. A hollow core photonic bandgap optical fibre according to claim 1 , in which the cladding comprises nine concentric rings of capillaries around the core, the core size ratio is 1.45 or above, and the optical transmission loss is 1.0 dB/km or less for a wavelength of 2000 nm.
14. A hollow core photonic bandgap optical fibre according to claim 13 , in which the first ring ratio is 0.80 or above, and the optical transmission loss is 0.8 dB/km or less for a wavelength of 2000 nm.
15. A hollow core photonic bandgap optical fibre according to claim 1 , in which the cladding is formed from one or more undoped or doped silicate glasses.
16. A hollow core photonic bandgap optical fibre according to claim 1 , wherein the cladding includes cells in second and subsequent rings surrounding the first ring, wherein the cells in the second and subsequent rings have an undistorted radial thickness.