Abstract: An optical fiber and an optical amplifier including the optical fiber are disclosed, the optical fiber includes a core region for guiding a propagation of a multimode optical signal, a cladding region laterally surrounding the core region and at least two doped rings, each of the at least two doped rings having a corresponding rare-earth or transition metal dopant concentration. The core region includes a central core having a first refractive index, at least one core layer laterally surrounding the central core, each of the at least one core layer having corresponding internal and external radii, an internal radius of an innermost core layer corresponding to a radius of the central core and an external radius of the outermost core layer corresponding to a radius of the core region.

Abstract: An optical fiber configured to improve the pump conversion efficiency of an L-band fiber amplifier which uses the multimode pump source. By directly absorbing multimode light including 915 nm, an active fiber core region co-doped with both erbium and ytterbium can provide gain to the L-band signals via stimulated emission. The unwanted C-band amplified spontaneous emission (ASE) light generate from this active fiber core region can be absorbed by another active fiber core region doped with erbium, then provides additional gain to the L-band signals. Active regions and cladding can be configured to match a given spatial mode of the optical signal. Signal-pump combiners with end-coupling or side coupling can be used.

Abstract: There is described a method of optically coupling a first optical fiber and a second optical fiber to one another. The method generally has a step of bringing a free end of the first optical fiber, the second optical fiber and liquid in close proximity to one another within a coupling region, the free end of the first optical fiber having a dimension below a critical dimension, the free end of the first optical fiber moving within said liquid to contact the second optical fiber along a given coupling length, said contact optically coupling the free end of the first optical fiber and the second optical fiber to one another.