Abstract: A system for the Raman amplification of mode-division multiplexed optical signals at the telecom wavelengths in multimode optical fibers, and a method. A mode-division multiplexer (105) is used at the input of a multimode fiber (107) to inject signals (101), and continuous-wave pump waves at lower wavelength (102), on the different transverse modes of the fiber. A second mode-division multiplexer (106) is used at the output of the fiber to extract the amplified signals (103). The amplification of one or more signals is accomplished by inter-modal and intra-modal stimulated Raman scattering occurring between the fiber transverse modes carrying the signals and those carrying the pumps.

Abstract: A wave guide may have an index profile including at least one maximum. The maximum or maxima of the index profile may correspond respectively to at least one maximum intensity of the outlet radiation with a mode of desired order. The wave guide may also have at least one doping ion configured to absorb the pump radiation. The doping ion or ions may have a concentration profile of doping ions including at least one maximum.