Patent ID: 7266275

Claim:
An optical fibre for transmitting light of at least one predetermined wavelength λ, the optical fibre having a longitudinal direction and a cross-section perpendicular thereto, the optical fibre comprising: (a) a core region comprising a core material of refractive index n c ; and (b) a cladding region, said cladding region surrounding said core region and comprising low-index cladding features of refractive index n 1 arranged in a background cladding material of refractive index n b ; said cladding region further comprising first inner cladding features of refractive index n 1 and second inner cladding features of refractive index n 2 , where n 2 is lower than n c , and n 2 is higher than n 1 , and said first inner cladding features and said second inner cladding features are arranged proximal to said core region, and n 2 is lower than n b .