Abstract: The invention relates to a high power amplifier waveguide for amplifying an optical signal wherein photo darkening due to high optical flux is reduced considerably. This is achieved by providing a cladding pumped amplifier waveguide wherein the optical mode overlap to the active material of the waveguide is low and/or wherein the active material is distributed over a large cross sectional region of the waveguide.

Abstract: The invention relates to a high power amplifier waveguide for amplifying an optical signal wherein photo darkening due to high optical flux is reduced considerably. This is achieved by providing a cladding pumped amplifier waveguide wherein the optical mode overlap to the active material of the waveguide is low and/or wherein the active material is distributed over a large cross sectional region of the waveguide.

Abstract: The invention relates to an optical fiber defining a longitudinal direction, the optical fiber comprising a core having a diameter larger than 10 ?m, said core comprises at least two solid segments of different composition, at least one of the segments comprises a photo-sensitive material. The core may be segmented in its cross-sectional direction and/or in its longitudinal direction. The optical fiber may comprise a Bragg grating written in at least one of said solid core segments In a preferred embodiment the optical fiber comprises a core with an effective refractive index ncore, and a cladding surrounding said core, wherein in a cross-section perpendicular to said longitudinal direction, said core being segmented, said core comprising a first core segment with an area a1 and a second core segment with an area a2; said first core segment comprises at least one photo-sensitive material, such as Ge and/or B and/or P doped silica; said second core segment surrounds said first core segment.

Abstract: An optical fiber having a longitudinal direction and a cross-section perpendicular thereto, said fiber in a cross-section comprising: (a) a core region (11) having a refractive index profile with a highest refractive index nc, and (b) a cladding region comprising cladding features (10) having a center-to-center spacing, ?, and a diameter, d, of around 0.4? or larger, wherein nc, ? and d are adapted such that the fiber exhibits zero dispersion wavelength of a fundamental mode in the wavelength range from 1530 nm to 1640 nm; a method of producing such a fiber; and use of such an optical fiber in e.g. an optical communication system, in an optical fiber laser, in an optical fiber amplifier, in an optical fiber Raman amplifier, in a dispersion compensator, in a dispersion and/or dispersion slope compensator.