In the thesis the problem of laser power scaling and brightness improvement is addressed. The limits that the development of single laser devices (both semiconductor lasers and fiber lasers) has reached and hardly can overpass have been discussed and an overview on the different techniques to combine multiple lasers into a single beam with greater power and quality has been presented. Between them, for the promising results that have already been obtained and its importance in future research, coherent combining techniques have been investigated in detail. For this reason, a Master Oscillator Power Amplifier (MOPA) system seeded with a fiber laser have been numerically simulated on Matlab and the Stochastic Parallel Gradient Descent (SPGD) algorithm to actively correct the phase of the channels and maximize the on-axis intensity of the combined beam has been validated.