A waveguide can have a first longitudinal section, with at least one core having a first refractive index and at least one sheath surrounding the core. The sheath can be made of a material having a second refractive index so the waveguide will guide at least one optical signal in the core. A third longitudinal section has a sheath and a coating surrounding the sheath having a third refractive index so the third longitudinal section of the waveguide will guide at least one optical signal in the sheath. A second longitudinal section, arranged between the first longitudinal section and the third longitudinal section being adapted to guide an optical signal from the core into the sheath.