Influence of the carrier density dependence of the absorption on the harmonic distortion in semiconductor lasers

It is shown that the carrier density dependence of the absorption can result in a significant increase of the harmonic distortion caused by gain suppression or by spatial hole burning in distributed-feedback (DFB)-lasers. This carrier density dependence of the absorption is often neglected in theoretical studies, but the author found that it may result in a dominant contribution to the second-order distortion in the AM response, especially at high output powers. The distortion then mainly depends on material parameters such as differential gain, differential absorption and the gain suppression coefficient.