Nonlinear gain dynamics in quantum-dot optical amplifiers and itsapplication to optical communication devices

摘要

Ultrafast gain dynamics in quantum-dot (QD) optical amplifiers hasnbeen studied. It was found that there are at least three nonlinearnprocesses, which are attributed to carrier relaxation to the groundnstates, phonon scattering, and carrier capture from the wetting layersninto the QDs. The relevant time constants were evaluated to be ~90 fs,n~260 fs, and ~3 ps, respectively, under a 50-mA bias condition. Thendephasing time was evaluated to be ~85 fs. The third-order opticalnsusceptibility (Χ(3)) has been evaluated by means of bothnnonlinear transmission and four-wave mixing experiments. The resultsnshow that the nonlinearity expressed bynΧ(3)/g0 is quite similar to that of bulk andnquantum wells, which can be explained by similar relaxation times.nApplications to optical communication devices are also discussed