InAs/GaAs Quantum Dot Dual-Mode Distributed Feedback Laser Towards Large Tuning Range Continuous-Wave Terahertz Application

In this paper, a laterally coupled distributed feedback (LC-DFB) laser based on modulation p-doped multiple InAs/GaAs quantum dot (QD) structures has been fabricated. The device exhibits a high side-mode suppression ratio (SMSR) of > 47 dB and a high thermal stability of dλ/dT = 0.092 nm/K under continuous-wave (CW) operation, which is mainly attributed to the high material gain prepared by modulation p-doping and rapid thermal annealing (RTA) process, and the significantly reduced waveguide losses by shallow-etched gratings and its close proximity to the laser ridge feature in the LC-DFB laser. With this superior performance of the DFB laser, the wide tunable dual-wavelength lasing operation has been obtained by delicately defining different periods for the grating structures on the two sides of the laser ridge or combining the reduced laser cavity length. The wavelength spacing between the two lasing modes can be flexibly tuned in a very wide range from 0.5 to 73.4 nm, corresponding to the frequency difference from 0.10 to 14 THz, which is the largest tuning range by the utilization of single device and hence providing a new opportunity towards the generation of CW THz radiation.