Optical amplifier

摘要

The present invention provides a two stage optical fibre amplifier wherein the first stage of the amplifier is coupled via a first coupler to a first pump source producing pump radiation of a first wavelength and the second stage of the amplifier is coupled via a second coupler to a second pump source producing radiation of a second wavelength characterised in that residual pump radiation from one of the amplifier stages is usable for amplification in the other amplifier stage and wherein the amplifier includes locking prevention means for preventing radiation of the first wavelength from reaching the second pump source and also stopping radiation of the second wavelength from reaching the first pump source.