Micro-structured optical fibre

An optical fibre according to any of the preceding claims, wherein any distance L from the inner boundary of a high index region to the outer boundary of a following low index region taken along a radial direction in the cross-sectional plane is larger than or equal to a minimum length Lmin and below or equal to a maximum length Lmax, where Lmax is two times Lmin.

An optical fibre according to any of the preceding claims, wherein at least 6 spaced apart low index type cladding regions each have a radial width being larger than a predetermined wavelength of light to be guided by the fibre, while said radial width is smaller than three times the-predetermined wavelength of light to be guided by the fibre.

An optical fibre according to any of the preceding claims in which at least 6 spaced apart low index type cladding regions each have a radial width being larger than 1.5 μm, such as larger than 2.0 μm, such as larger than 2.5 μm, such as larger than 3.0 μm, such as larger than 3.5 μm, such as larger than 4.0 μm, such as larger than 4.5 μm.

An optical fibre according to any of the preceding claims, wherein each of the second plurality of concentric cladding regions are made of a solid material with no cladding features.

An optical fibre according to any of the preceding claims, wherein the spaced apart first cladding features within a given first cladding region are spaced at substantially equal distances.

An optical fibre according to any of the preceding claims, wherein the first cladding features are arranged in a locally two-dimensionally periodic structure within each or at least part of said first cladding regions.

An optical fibre according to any of the preceding claims, wherein the spaced apart second cladding features within a given second cladding region are spaced at substantially equal distances.

An optical fibre according to any of the preceding claims, wherein the second cladding features are arranged in a locally two-dimensionally periodic structure within each or at least part of said second cladding regions.

An optical fibre according to any of the preceding claims, wherein the shape of the inner and outer boundaries of the cladding regions is substantially circular or elliptical.

An optical fibre according to any of the preceding claims, wherein the centres of the plurality of spaced apart first cladding features are arranged essentially at even distances within each or at least part of said first cladding regions.

An optical fibre according to any of the preceding claims, wherein the centres of the plurality of spaced apart second cladding features are arranged essentially at even distances within each or at least part of said second cladding regions.

An optical fibre according to any of the preceding claims, wherein the core region comprises a hollow core.

An optical fibre according to any of the preceding claims, wherein the ratio of the radial widths of the radial widest and the radial most narrow of the concentric cladding regions is less than 4, such as less than 3, such as less than 2, such as less than 1.5, such as less than 1.2, such as less than 1.1.

An optical fibre according to any of the preceding claims, wherein each of the concentric cladding regions has the same background refractive index.

An optical fibre according to any of the preceding claims, wherein the background material of at least one of the concentric cladding regions is a dielectric material such as silica with a refractive index in the range of 1.43 to 1.49, such as around 1.45.

An optical fibre according to any of the preceding claims, wherein the center of any of the spaced apart cladding features is situated near the center of another spaced apart cladding feature at a distance smaller than 5.0 μm, such as smaller than 2.0 μm, such as smaller than 1.0 μm, such as smaller than 0.7 μm, such as smaller than 0.4 μm, such as smaller than 0.2 μm, such as smaller than 0.1 μm.

An optical fibre according to any of the preceding claims, wherein the largest cross-sectional dimension of any one of the spaced apart cladding features is smaller than 5.0 μm, such as smaller than 2.0 μm, such as smaller than 1.0 μm, such as smaller than 0.7 μm, such as smaller than 0.4 μm, such as smaller than 0.2 μm, such as smaller than 0.1 μm.

An optical fibre according to any of the preceding claims, wherein the value of the radial widest width of any of the cladding regions divided by a predetermined wavelength to be guided by the fibre is less than 3.0, such as less than 2.0, such as less than 1.5, such as less than 1.0, such as less than 0.5, such as less than 0.3.

An optical fibre according to any of the preceding claims, wherein the spaced apart cladding features are voids.

An optical fibre according to any of the preceding claims, wherein the spaced apart cladding features contain air or another gas, or contain water, oil, gasoline or another liquid.

An optical fibre according to any of the preceding claims, wherein each of the first plurality of low index cladding regions has a geometrical index being lower than 1.25, such as lower than 1.2, such as lower than 1.15, such as lower than 1.1, such as lower than 1.05.

An optical fibre according to any of the preceding claims, wherein the geometrical index of the high index cladding region with the lowest geometrical index is more than 5% larger than the geometrical index of the low index cladding region with the highest geometrical index, such as more than 10% larger, such as more than 20% larger, such as more than 25% larger, such as more than 30% larger, such as more than 35% larger, such as more than 40% larger, such as more than 45% larger.

An optical fibre according to any of the preceding claims, wherein the core region has a largest cross-sectional dimension being larger than 1 μm, such as larger than 2 μm, such as larger than 4 μm, such as larger than 8 μm, such as larger than 15 μm, such as larger than 30 μm.

A method of using an optical fibre according to any of the preceding claims in a process involving third order harmonic generation or the reversed process.