Multimode emission and optical power in a semiconductor quantum dot laser.

Effect of spatial hole burning (SHB) and multi-longitudinal-mode generation on high power operation of a quantum dot (QD) laser is studied. We use a set of rate equations for confined carriers in QDs, free carriers in the optical confinement layer and photons. The threshold currents and output powers of modes are computed numerically. The power of the main mode is reduced due to lasing of higher-order modes and spatially nonuniform carrier distribution. As a new mode turns on, kinks appear in the light-current curves (LCCs) of existing modes. SHB reduces the total optical power of a laser and contributes to nonlinearity of the overall LCC. The effect is more significant when any of the parameters of the structure is close to its critical tolerable value. The LCC becomes more linear with improving QD-size uniformity or increasing surface density of QDs or cavity length.