Ultra-high-speed modulation of 1.3-micron InGaAsP diode lasers

The differential gain of 1.3-micron InGaAsP lasers is found to be a strong function of the active layer doping level. Using devices with doping enhanced differential gain and short cavity lengths, a modulation bandwidth of 15 GHz is achieved. The parasitic shunt capacitance which often severely limits the modulation bandwidth of diode lasers is greatly reduced by using a 0.4-micron thick oxide isolation layer and a device structure which minimizes parasitic capacitances. It is found that nonlinear gain saturation predominantly determines the damping factor of these devices, and thus greatly influences their modulation characteristics. These data directly show that the damping factor of multilongitudinal-mode lasers is smaller than that of single-mode lasers, suggesting that wider modulation bandwidths can be achieved with multimode devices than with single-mode devices.