Patent ID: 8837887

Claim:
A waveguide comprising a first longitudinal section, comprising at least one core with a first refractive index and at least one sheath surrounding said core, said sheath comprising a material having a second refractive index, and said waveguide being adapted to guide at least one optical signal in the core, a third longitudinal section comprising a sheath and a coating surrounding said sheath and comprising a material having a third refractive index, said third longitudinal section of the waveguide being adapted to guide at least one optical signal in the sheath, and a second longitudinal section, being arranged between the first longitudinal section and the third longitudinal section and wherein the diameter of the core decreases over the length of the second longitudinal section from an initial value to a final value; wherein parameters V = π · d K · n K 2 - n M 2 λ in the first and second longitudinal sections and parameter V = π · d M · n M 2 - n B 2 λ in the third longitudinal section differ from one another by less than 5%, less than 2% or less than 0.5%, where n K is the first refractive index, n M is the second refractive index, n B is the third refractive index, d K is the diameter of the core, d M is the diameter of the sheath, and λ is the wavelength of the optical signal which may be conducted in the waveguide.