Han Xue Zhao

Two-state competition in 1.3 μm multilayer InAs/InGaAs quantum dot lasers

The competition of ground state (GS) and excited state (ES) is investigated from the as-grown and thermally annealed 1.3 μm ten-layer p-doped InAs/GaAs quantum dot (QD) lasers. The modal gain competition between GS and ES are measured and analyzed around the ES threshold characteristics. Our results show that two-state competition is more significant in devices with short cavity length operating at high temperature. By comparing the as-grown and annealed devices, we demonstrate enhanced GS and suppressed ES lasing from the QD laser annealed at 600 °C for 15 s.

Temperature Characteristics of Gain Profiles in 1.3-

The modal gain and differential gain of 1.3-mum p-doped and undoped InAs/GaAs quantum-dot (QD) lasers have been investigated as a function of injection current under different operation temperatures. The results show that p-doping improves the modal and differential gains in QD lasers at high temperatures. Exponential decrease in the differential gain profiles were observed in both types of lasers from 20degC to 80degC. Theoretical calculations based on the rate equation model for the undoped QD laser gain at different temperatures are presented.

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The modal gain and differential gain of 1.3-μm InAs-GaAs quantum-dot (QD) lasers with different doping concentrations have been investigated as a function of injection current under different operation temperatures from 20°C to 120°C. The results show that QD laser with light doping density can improve the characteristic temperature (To), modal gain, and differential gain and reduce the threshold current density.

-Doped and Undoped InAs/GaAs Quantum-Dot Lasers

We investigated the effects of rapid thermal annealing (RTA) on the dynamic characteristics of the InAs/GaAs ten-layer quantum dot (QD) laser. Improvements in the temperature stability of bandwidth have been demonstrated upon annealing. We attribute the improvements to the following factors: 1) increase in internal quantum efficiency and 2) reduction in temperature dependency of differential gain. The increase in bandwidth at high temperature from the annealed QDs could be due to a reduction in the relaxation time on the order of 0.1 ps. More importantly, the RTA process resulted in better temperature stability in the differential gain and gain compression. This is beneficial for the development of uncooled high-speed QD lasers.

Temperature-Dependent Study on Modal Gain and Differential Gain of 1.3-

InAs-InGaAs-GaAs quantum-dot (QD) structures are extensively investigated for 1.3- lasers with applications in low-cost metropolitan access and local area networks. For the purpose of monolithic integration, realization of QD electroabsorption modulators (EAMs) is equally important. However, there are few research efforts on InAs-InGaAs-GaAs QDs for EAMs. Furthermore, existing results either demonstrate low extinction ratio ( 5 dB) or multimode profile, i.e., unsuitable for practical applications. In this work, we investigated the electroabsorption characteristics of a single-mode 1.3- InAs-InGaAs-GaAs ten-layer QD waveguide. The obtained extinction ratio of 13 dB from the single-mode QD waveguide demonstrates the feasibility of implementing QD-EAM for practical applications. We believe that our findings will be beneficial for researchers working on the monolithic integration of the QD laser and modulator.

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The characteristic temperature (<i>T</i>₀) and modal gain of 1.3-μm p-doped InAs/GaAs quantum-dot (QD) lasers with different ridge heights (<i>h</i>) have been investigated as a function of injection current under different operation temperatures ranging from 20°C to 120°C. The results show that the geometrical shape of the laser ridge has significant effect on the threshold current density, <i>T</i>₀, and modal gain. The optimum ridge height in the QD laser should be controlled with etch depth where most of the doped layers above the active region are removed.

m InAs–GaAs QD Lasers With Different

We investigate the influence of thermal effects on the high-speed performance of 1.3-μm InAs/GaAs quantum-dot lasers in a wide temperature range (5–50°C). Ridge waveguide devices with 1.1 mm cavity length exhibit small signal modulation bandwidths of 7.51 GHz at 5°C and 3.98 GHz at 50°C. Temperature-dependent K-factor, differential gain, and gain compression factor are studied. While the intrinsic damping-limited modulation bandwidth is as high as 23 GHz, the actual modulation bandwidth is limited by carrier thermalization under continuous wave operation. Saturation of the resonance frequency was found to be the result of thermal reduction in the differential gain, which may originate from carrier thermalization.

p

The self-heating effect in 1.3-μm InAs/GaAs quantum dot (QD) lasers with different doping levels has been investigated by comparing the characteristics of the threshold current density (<i>J</i>_th) and modal gain measured in continuous wave and pulsed modes with the heat sink temperature ranging from 20°C to 120°C. The results show that the <i>p</i>-doping can significantly reduce the self-heating effect in QD lasers.

-Doping Levels

We have explained the two-state lasing in QD lasers with different doping density by the laser modal gain behavior, and shown that the laser with relatively light doping density can largely suppress the exited-state lasing.