Carrier transport effects on pulse statistics of modulated quantum well lasers

摘要

Abstract: We perform a theoretical study of carrier transport effects on the pulse statistics of QW lasers modulated at GHz rates for different bias levels, I$-b$/, and modulation frequencies. The lasers considered are ultra-high speed In$- 0.35$/Ga$-0.65$/As/GaAs MQW lasers with intrinsic modulation bandwidths of 40GHz. A rate-equation model, including spontaneous emission noise, which incorporates the dynamics of the unconfined carriers in the core is used. Different values of the transport/capture time, $tau$-cap$/, and the re-emission time out of the QW's (escape time) $tau$-esc$/, are considered to illustrate carrier transport effects. Different bias currents near threshold are considered. In this way small enough turn-on delay times and good on-off ratio are obtained.It is found that for slow modulation the laser switch-on is delayed and the timing jitter is increased when $tau$-cap$/ increases and $tau$-esc$/ decreases. These detrimental effects are reduced at high rates. However, the maximum modulation frequency decreases when $tau$-cap$/ increases. Concerning the combined dependence of turn-on time of I$-b$/ and on the modulation frequency, the results are similar to those obtained for bulk lasers when $tau$-cap$/ is not very large, even for small $tau$-esc$/. Timing jitter becomes rather independent of the modulation frequency at GHz rates when biasing slightly below threshold. However, for large $tau$-cap$/ timing jitter increases with the modulation period. The dependence on the modulation frequency is due to the initial condition at the beginning of a pulse, that is very different from the steady state associated to I$-b$/. !24