Quantum dot nanostructures are one of the best practical examples of emerging nanotechnologies hence offering superior properties as compared to their quantum well counterparts. InAs/GaAs quantum dots allow producing energy- and cost-efficient devices with outstanding temperature stability, lowest threshold current, ultrafast gain dynamics, and low amplified spontaneous emission. This paper reports on the recent achievements in ultrafast and nonlinear dynamics properties of InAs/GaAs quantum dot lasers for radar systems, wireless communications and high-speed optical communications. Passive mode-locking is shown to exhibit a great potential for microwave, millimeter-wave and Terahertz signal generation with high repetition frequency tuning and jitter reduction. The optical feedback is also used to stabilize the pulse emission leading an integrated timing jitter as low as 90 fs without consuming additional power. Lastly, multimode optical feedback dynamics of InAs/GaAs QD lasers emitting on different lasing states is also studied. In particular, a chaos free operation is observed for the first time from the ground state lasing operation.
In this paper, we investigate the temperature dependence of spectral linewidth of InAs/InP quantum dot distributed feedback lasers. In comparison with their quantum well counterparts, results show that quantum dot lasers have spectral linewidths rather insensitive to the temperature with minimum values below 200 kHz in the range of 283K to 303K. The experimental results are also well confirmed by numerical simulations. Overall, this work shows that quantum dot lasers are excellent candidates for various applications such as coherent communication systems, high-resolution spectroscopy, high purity photonic microwave generation and on-chip atomic clocks.
Frequency conversion using highly non-degenerate four-wave mixing is reported in InAs/GaAs quantum-dot Fabry- Perot lasers. In order to compress the spontaneous emission noise, the laser is optically injection-locked. Under proper injection conditions, the beating between the injected light frequency and the cavity resonant frequency dominates the dynamic behavior and enhances a carrier modulation resonance at frequencies higher than the relaxation oscillation frequency. Conversion efficiencies as high as -12 dB associated to a large optical signal-to-noise ratio of 36 dB are reported. The conversion bandwidth is extended up to 2.1 THz for down-conversion (resp. 3.2 THz for up-conversion) with a quasi-symmetrical response between up- and down-converted signals.
In this work, the sensitivity to external optical feedback of two different InAs/GaAs QD Fabry-Perot (FP) lasers is investigated under long cavity regime. The first, which has a 1.5 mm-long cavity, emits on the GS while the second one, which is 1 mm long, radiates solely on the ES transition. The results indicate that for the same bias level, the ES laser presents a larger sensitivity to external feedback, the critical level being under 1% versus above 9% for the GS laser. In particular, the ES laser exhibits a route to chaos such that the first destabilization occurs for a lower feedback strength than for the GS laser.
Non-degenerate four-wave mixing effects are investigated in an injection-locked InAs/InP nanostructure Fabry-Perot laser. Locking a longitudinal mode at various wavelengths within the gain spectrum and using the locked mode as the pump for the wave mixing shows different levels of asymmetry between up- and down-conversion. Experiments reveal that the normalized conversion efficiency is less asymmetric when the pump is locked at wavelengths below that of the gain peak. The values of nonlinear conversion efficiencies are maintained above -60 dB for pump-probe frequency detunings up to 3.5 THz. The role of the linewidth enhancement factor on the asymmetry is discussed and the value of the nonlinear susceptibility is compared to similar InAs/InP nanostructure semiconductor optical amplifiers. From an end-user viewpoint, data transmission experiments have also confirmed the possibility to propagate up-converted signals over 100 km at a 5 Gb/s bit rate under an OOK modulation format.