Patent ID: 8903214

Claim:
A single-mode optical fiber for guiding an optical signal, said optical fiber having a longitudinal, optical axis and a cross section perpendicular thereto, said optical fiber comprising: a core region being capable of guiding an optical signal in a fundamental core mode with an effective refractive index, n c , at an optical signal wavelength, λ 1 ; a cladding region surrounding the core region, the cladding region comprising an inner cladding region and an outer cladding region, said inner cladding region comprising a background material having a refractive index, n b , and a plurality of inner cladding features arranged in said background material, wherein at least a plurality of said plurality of inner cladding features are of a first type of feature, said first type of feature comprising an air hole surrounded by a high-index region comprising a high-index material having a refractive index, n r , that is larger than the refractive index of the inner cladding background material, said first type of feature supports an optical mode with an effective refractive index, n 1 , which is lower than or equal to the effective refractive index of the fundamental core mode, n c , at said optical signal wavelength, λ 1 , wherein said core region has a maximum cross-sectional dimension of more than about 40 μm, and wherein the index difference between the high-index material and the background material of the inner cladding is below about 1.10 −2 .