Complete ground state gain recovery after ultrashort double pulses in quantum dot based semiconductor optical amplifier

Gain recovery dynamics are studied in electrically pumped quantum dot (QD) based semiconductor optical amplifiers (SOAs) after amplification of double femtosecond laser pulses using ultrafast pump-probe spectroscopy with heterodyne detection. The authors observe a distinct change in gain recovery in the ground state when a significant excited state population is achieved. A complete gain recovery is found when two $150\mathrm{fs}$ pulses with $5\mathrm{ps}$ time delay pass through the SOA in resonance to the ground state under high injection currents of $80–100\mathrm{mA}$ . The obtained results open the way for ultrafast $(>200\mathrm{GHz})$ operation in $p$ -doped QD based SOAs at $1.3\mu \mathrm{m}$ telecommunications wavelengths.