Numerical investigation on photonic microwave generation by a sole excited-state emitting quantum dot laser with optical injection and optical feedback*

Based on three-level exciton model, the enhanced photonic microwave signal generation by using a sole excited-state (ES) emitting quantum dot (QD) laser under both optical injection and optical feedback is numerically studied. Within the range of period-one (P1) dynamics caused by the optical injection, the variations of microwave frequency and microwave intensity with the parameters of frequency detuning and injection strength are demonstrated. It is found that the microwave frequency can be continuously tuned by adjusting the injection parameters, and the microwave intensity can be enhanced by changing the injection strength. Moreover, considering that the generated microwave has a wide linewidth, an optical feedback loop is further employed to compress the linewidth, and the effect of feedback parameters on the linewidth is investigated. It is found that with the increase of feedback strength or delay time, the linewidth is evidently decreased due to the locking effect. However, for the relatively large feedback strength or delay time, the linewidth compression effect becomes worse due to the gradually destroyed P1 dynamics. Besides, through optimizing the feedback parameters, the linewidth can be reduced by up to more than one order of magnitude for different microwave frequencies.