Optimized design of QD-LD toward QD-SOA to achieve 35-dB maximum chip gain with 400-mA injected current

We measured the characteristics of Quantum Dot Semiconductor Optical Amplifiers (QD-SOA) with 25 stacked layers of InAs/InGaAlAs QDs grown on InP(311)B substrate. The temperature dependence of threshold current and lasing peak wavelength in C-band of QD-Laser Diode (QD-LD) were analyzed over its operating range of 15-80 degrees C. The chip gains of 3 device lengths (1.5, 2 and 2.4 mm) were compared under varied injected currents up to 500 mA. To avoid overheat and chip damage during measurements, the pulse current source with 1% and 10% duty cycles was used. Based on our best results of 2-mm long QD-SOA with 25 stacked QD layers, the 1% pulse is preferable because of its lower heating and additional chip gain of 11.9 dB. Hence, the highest chip gain of 35 dB was achieved at 400-mA injected current, as well as the highest 3-dB saturation output power at 20.9 dBm. According to the plot of chip gain versus wavelength, it shows 3-dB gain spectrum over 20 nm and the highest peak at 1570-nm wavelength with 500-mA injected current. In addition, the results of another QD-SOA module showed 15.4-dB Input Power Dynamic Range (IPDR), faster response time due to less pattern effect and error-free transmission of 40 Gb/s data over 20-km Single Mode Fiber (SMF) link.