Crosstalk reduction in semiconductor laser amplifiers

One of the important deficiencies of semiconductor laser amplifiers, compared with fibre amplifiers, is the crosstalk that is created by four-wave mixing and gain saturation. If the electron density were controlled at all points along the amplifier, the crosstalk could be greatly reduced. The paper looks at the theory of optoelectronic feedback, using the spontaneous emission as a measure of the electron density and introducing both linear and differential feedback into the injected current, to control the electron density in an amplifier. The paper also examines the consequential reductions in four-wave mixing. It is concluded that it may be feasible to effect this, particularly in an integrated amplifier. Preliminary practical trials are under way