Micro-structured optical fiber

An optical fibre for transmitting light, said optical fibre having an axial direction and a cross-section perpendicular to said axial direction, said optical fibre comprising:

• a core region, and
• a micro-structured cladding surrounding said core region, wherein
• the cladding comprises a number of successive concentric cladding regions encompassing said core region, each of said concentric cladding regions having inner and outer boundaries of substantially similar cross-sectional shape and a substantially constant background refractive index,
• a first plurality of the concentric cladding regions being of a low index type, each of said first cladding regions comprising a plurality of spaced apart first cladding features elongated in the fibre axial direction, each of said first cladding feature having a refractive index being lower than the background refractive index of the cladding region comprising the cladding feature, and each said first cladding feature having a largest cross-sectional dimension being smaller than or equal to the distance between the inner and the outer boundary of the cladding region comprising the cladding feature, whereby the geometrical index of a cladding region of the first type is lowered,
• a second plurality of the concentric cladding regions being of a high index type having a geometrical index being higher than the geometrical index of each of the first plurality of cladding regions,
• said high index type and low index type cladding regions being alternating arranged so that each low index region at its outer boundary is encompassed by a high index region, and
• wherein the arrangement of cladding features in relation to the micro-structured cladding as a whole is a non-periodic arrangement in the cross-sectional plane.