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

Abstract

This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.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 À1 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.

Twofold gain enhancement by elongation of QDs in polarization preserving QD-SOAs

“…Except for the stimulated emission rate, all rates depend on a specific lifetime and QD state occupation probability. While the spontaneous emission lifetime is treated as a constant, the relaxation and excitation lifetimes depend on the wetting layer carrier density ( 6)- (8).…”

“…Ultrafast gain recovery and pronounced nonlinear effects 3 substantiate the high potential of QD-SOAs in the fields of high frequency signal amplification, all-optical data processing and wavelength conversion using four-wave-mixing (FWM) [4][5][6][7] . Devices with modulation frequencies exceeding 200 GHz 8 and a 120 nm broadband gain with saturation output powers above 20 dB facilitate wavelength division multiplexing 9,10 and high efficiency symmetric FWM. 11 Furthermore, several experimental and theoretical works have shown that, using closely stacked QDs, polarization preserving amplification can be realized.…”

Laser Characteristic and Strain Distribution Dependence on Embedding Layer Thickness of Quantum Dots Laser Diodes Grown on InP(311)B Substrate

“…Therefore, this study also focused on QDs, employing the strain compensation technique, [ 25,26 ] which enables a highly stacked QD structure with more than 300 layers, [ 25 ] owing to the prevention of the degradation of the QD quality, and QD‐SOAs and QD‐LDs were successfully fabricated in the 1.55 μm band grown on an InP(311)B substrate. [ 27–31 ] Moreover, this study already demonstrated heterogeneous integrated devices, such as tunable LDs [ 32–34 ] and dual‐wavelength lasers, for the signal source in the access network that used radio over fiber technique, [ 35 ] with QD‐and Si photonics‐based PICs in the O‐band and 1 μm band (1.0−1.26 μm, which we call T‐band). [ 36 ] However, the threshold current of the fabricated QD‐LD was insufficient because the design of the device was not optimized.…”

Influence and its Optimal Design of Number of Stacked Layer in Quantum‐Dot Lasers

“…Several groups have reported that laser diodes (LDs), semiconductor optical amplifiers (SOAs), and photodiodes (PDs) that utilize QD structures have displayed high performance in terms of high thermal stability, low threshold, wide operation bandwidth, and ultra‐fast response . In our previous studies, employing the strain compensation technique, we successfully fabricated QD‐SOAs and QD‐LDs in the 1.55 μm‐band grown on an InP(311)B substrate, which enables highly stacked QD structure up to more than 300 layers, and demonstrated that ultra‐fast operation over 220 Gb/s class speed of QD‐SOA and a characteristic temperature ( T 0 ) of more than 2000 K of QD‐LD utilizing a delta‐doping method of p‐dopants, could be achieved. However, the threshold current of our fabricated QD‐LD was not as small because the design of the device was not optimized .…”