Modulation response of Quantum Well lasers with carrier transport effects under weak optical feedback

We theoretically investigate the influence of optical feedback on the modulation response of quantum-well lasers. Controlled weak optical feedback is shown to be useful in overcoming the high frequency limitations imposed by carrier-transport effects. With a fine tuning of the external cavity length the maximum attainable modulation bandwidth can be increased. Modulation bandwidths (f 3dB ) higher than in bulk devices have been recently demonstrated in Quantum-Well (QW) lasers, achieving 40 GHz [1] and 25 GHz [2] for InGaAs/GaAs and InGaAsP/InP material systems, respectively. However, while the maximum intrinsic modulation bandwidth f max 3dB is limited in bulk lasers by damping, carrier transport introduces additional limitations in QW lasers [3, 4]. For bulk lasers f max 3dB is expressed in terms of the K-factor as f max 3dB ß 8:9=K [5], with K = 4ß 2 (ø p + ffl g gn ) (see Table I for parameter definitions). Carrier transport in QW lasers, including carrier diffusion acr..