Small-signal cross-gain modulation and crosstalk characteristics of quantum dot semiconductor optical amplifiers at 1.3 μm

We present experimental and numerical results of the highspeed small-signal cross-gain modulation (XGM) and crosstalk of quantum-dot (QD) semiconductor optical amplifiers (SOAs) operating at 1.3 μm. The measured small-signal XGM responses at various injection currents show that they can be enhanced by injecting more carriers to the QD carrier reservoir. The calculated results of gain saturation in QD SOAs, based on multiple couple-rate equations, demonstrates that the enhanced XGM responses at high injection current is due to the transition of the main XGM mechanism from slow total carrier density depletion to ultrafast spectra hole burning. The calculated small-signal crosstalk becomes larger at high injection current, which is similar to the high-speed XGM responses.