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Abstract

An optical fibre structure usable in amplifying optical signals, comprising a length of optical fibre (1) which includes two uniformally spaced monomode optical cores (2,4) located within a common cladding (6) so as to provide two optical guidance paths, the optical characteristics of at least the cores being different such as to give the two guidance paths different propagation constants the values of which coincide for a predetermined coupling wavelength, one of the cores including a fluorescent material capable of producing stimulated emission. There is also disclosed a method of amplifying an optical signal using such an optical fibre structure, comprising arranging for the wavelength (.lambda..sub.s) of the optical signal, the fluorescent wavelength of said material in said one core, and said predetermined coupling wavelength all to be substantially the same, launching optical pump energy having a different wavelength (.lambda..sub.p) into said one core to pump the fluorescent material, launching the optical signal into the other core so that the optical signal transfers repeatedly between the two cores due to optical coupling and, when in said one core, gives rise to stimulated emission substantially at its own wavelength from the fluorescent material thereby becoming amplified, and extracting the amplified optical signal from the fibre structure when it is in said other core. A device (FIG. 4) using this method is also disclosed.

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