Abstract
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.
Highlights
Distributed feedback (DFB) lasers are technologically significant for their wide range of applications in long-distance fiber optical communication and terahertz (THz) radiation due to their narrow emission spectrum and stabilized emission wavelength [1–3]
To avoid the re-growth process, Goshima et al proposed a quantum dot (QD)-based laterally coupled distributed feedback (LC-DFB) laser structure which was realized by deeply etching the grating vertically into the ridge waveguide, but low slope efficiencies below 0.03 W/A and small side-mode suppression ratio (SMSR) of 20 dB were observed due to large waveguide losses [10]
Our work demonstrates the promise applications of QD-based LC-DFB lasers for long-distance fiber-optic communication and CW THz radiation sources
Summary
Distributed feedback (DFB) lasers are technologically significant for their wide range of applications in long-distance fiber optical communication and terahertz (THz) radiation due to their narrow emission spectrum and stabilized emission wavelength [1–3]. CW THz signals can be generated by using two independent DFB laser beams of slightly different frequencies This technique has emerged as an excellent choice to generate THz radiation benefitting from the very narrow emission spectrum and stabilized emission wavelength of DFB laser diodes [3, 16–18]. Dual-mode lasing was successfully obtained with the LC-DFB lasers by fabricating two sets of gratings of different periods, and the lasing wavelengths can be manipulated by delicately modifying the grating periods, which enable a large range tuning of the frequency difference of the two lasing modes from 0.10 to 14 THz. Our work demonstrates the promise applications of QD-based LC-DFB lasers for long-distance fiber-optic communication and CW THz radiation sources
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