Analog Modulation of 1.55μm Vertical-Cavity Lasers

We analyze the performance of InP/GaAs fused 1.55μm vertical-cavity lasers (VCLs) under analog modulation. Our VCLs employ a strain-compensated InGaAsP/InP multi-quantum well (MQW) active region sandwiched between two AlGaAs/GaAs distributed Bragg reflectors (DBRs). The first AlGaAs layer of the p-doped top mirror is laterally oxidized for optical and electrical confinement. These devices exhibit the lowest threshold current as well as the highest temperature of continuous-wave operation of any electrically pumped long-wavelength VCL. Two different device designs are investigated and compared. Reduction of the MQW barrier strain and enhancement of the optical index guiding by the oxide layer lead to an improvement of VCL performance. However, parasitic effects limit the modulation bandwidth. Higher order harmonic distortion is measured and simulated using a rate equation model. The model includes a non-linear gain function, gain compression, spontaneous emission and Auger recombination as well as carrier density dependent absorption in the quantum wells which reduces the differential gain. The good agreement between measurement and simulation indicates that electronphoton interaction within the quantum wells dominates the non-linear distortion. Multiple higher order response peaks are measured and reproduced by the model.