Abstract: The present disclosure relates to a multimode optical waveguide comprising a cladding and a core. The core of the multimode optical waveguide has a polygonal cross-section. The core forms a coil spun around the longitudinal axis of the cladding. The multimode optical waveguide may be used to realize a mode scrambler and a mode conditioner.

Abstract: Multi-cladding optical fibers to be used in the context of fiber amplifiers and fiber lasers are described herein. Embodiments of optical fibers include a rare-earth doped core into which the signal field is to be amplified. The doped core is surrounded by multiple claddings that guide the pump field to be absorbed by the reactive core material. The first cladding has a depressed refractive index to improve high-order mode bending losses without incurring significant fundamental mode bending losses.

Abstract: The invention provides a multi-clad fiber, with three claddings or more, where at least one intermediate cladding is inserted between an inner core and an outer core of the multi-clad fiber, for enlarging the cross-section of the fiber core or for increasing the dopant density in the core. The invention also provides an intermediate cladding having a multi-layer structure to better confine the pump power in a suitable pumping region of the fiber.

Abstract: An optical fiber comprises a singlemode core, and an inner cladding disposed around said core, an intermediate cladding disposed around said inner cladding and an outer cladding disposed around said intermediate cladding thereby forming a triple-clad geometry. The core is doped with rare-earth elements and represents the waveguide section of higher refractive index through which the signal is transmitted and amplified. A fiber coating is provided around said outer cladding. The core has a higher refractive index than said inner cladding, said inner cladding having a higher refractive index than said intermediate cladding, and said intermediate cladding having a higher refractive index than said outer cladding. The inner cladding has a fairly high refractive index to limit the numerical aperture (NA) of said core.

Abstract: An all-glass multi-clad polygon-shaped convex optical fiber comprises a core having a core refractive index, a first glass cladding disposed around the core and having a first cladding refractive index that is lower than the core refractive index of the core, and at least a second glass cladding disposed around the first glass cladding and having a second cladding refractive index that is lower than the first cladding refractive index. The first and second claddings each have a convex polygonal cross-section, e.g. octagonal cross-sections. A method for fabricating such an optical fiber comprises the steps of: (i) mechanically machining an all-glass optical fiber preform having a core and a first cladding into an optical fiber preform having a convex polygonal cross-section; and (ii) fusing at least another glass cladding to the optical fiber preform, thereby resulting in the all-glass multi-clad polygon-shaped convex optical fiber.