WELL-BARRIER HOLE BURNING IN QUANTUM-WELL LASERS

The reported wide variations in the damping behavior of quantum well lasers are explained by a novel theory of nonlinear gain, well-barrier hole burning. It is shown that with increasing photon density, carriers build up in the higher bandgap barrier/confinement layers due to a nonzero capture time recently measured in quantum well amplifiers. In analogy with spectral hole burning, this spatial hole perpendicular to the active region acts under certain circumstances like an additional photon-dependent gain suppression (1 - epsilon-S), with epsilon = tau-cap dg / dn upsilon-g n(eq)2 where tau-cap is the effective capture time and eta-eq is the equilibrium ratio between the number of carriers in the barriers and those in the wells. This additional damping is shown to be consistent with anomalously high damping rates found in some quantum well lasers. Design considerations to reduce this additional damping term are discussed.