Dynamic characteristics of 20‐layer stacked QD‐SOA with strain compensation technique by ultrafast signals using optical frequency comb

Abstract

In this article, we evaluated the static and dynamic characteristics of 20‐layer stacked quantum dot semiconductor optical amplifiers (QD‐SOAs) grown on an InP(311)B substrate with a strain compensation technique by ultrafast signals using an optical frequency comb. The gain peak wavelength of the fabricated QD‐SOA was 1520 nm, and a maximum gain of approximately 15.8 dB was obtained when the injection current was 350 mA. By using optical bit rate multiplier modules, an optical pulse, which was generated by the use of the optical frequency comb, was multiplexed. We observed the dynamic behavior of the QD‐SOA with the pulse trains. The minimum interval between pulses was 4.2 ps, and we measured using an optical sampling oscilloscope. It was found the QD‐SOA could respond to ultrafast pulses that were equivalent to the signals of 220 Gb s−1 class speed without any large pattern distortions. In addition, we could obtain a rather clear optical pulse waveform. We also estimated the gain recovery time of the QD‐SOA to be 6.0 ps by using a pump probe‐like method. One of the reasons that the fabricated QD‐SOA could respond to ultrafast signals was its ultrashort gain recovery time.