The results obtained from luminescence measurements made on one-dimensional optical amplifiers are reviewed. The investigated samples are GaAs/(Ga, Al)As waveguiding structures containing a multiple quantum well structure as active element. The experimental data are compared with the results of a numerical self-consistent model of the optical amplifier. The observed spatial dependencies of carrier and luminous densities are found to agree in a semi-quantitative way with the theoretical predictions. Saturation of optical amplification is caused by carrier depopulation through stimulated recombination, and by the loss of light caused by scattering at sample defects and/or imperfect waveguiding. It is argued that the discrepancies found on the high-energy side of the grain spectra are caused by reabsorption of amplified light at the edges of the amplifier.