Patent ID: 6856742

Claim:
A micro-structured optical fibre for guiding light at an operating wavelength, said optical fibre having an axial direction and a cross section perpendicular to said axial direction, said optical fibre comprising: a core region, an inner cladding region surrounding said core region, said cladding region comprising a multiplicity of spaced apart inner cladding features that are elongated in the fibre axial direction and disposed in an inner cladding material, said inner cladding features having a smallest cross-sectional dimension, d i,min , and a largest cross-sectional dimension, d i,max , and having a centre-to-centre spacing, Λ i , between two neighbouring inner cladding features, an outer cladding region surrounding said inner cladding region, said outer cladding region comprising a multiplicity of spaced apart outer cladding features that are elongated in the fibre axial direction and disposed in an outer cladding material, at least part of said outer cladding features having a smallest cross-sectional dimension, d o,min , and having a centre-to-centre spacing, Λ o , between two neighbouring inner cladding features, wherein d i,min is in the range from 0.35Λ i to 0.50Λ i , d o,min is in the range from 0.50Λ o to 0.90Λ o , d i,min is smaller than d o,min , and Λ i is larger than 2.0 μm.