Zun-Ren Lv

Dynamic characteristics of two-state lasing quantum dot lasers under large signal modulation

Large signal modulation characteristics of the simultaneous ground-state (GS) and excited-state (ES) lasing quantum dot lasers are theoretically investigated. Relaxation oscillations of ‘0 → 1’ and ‘1 → 0’ in the GS lasing region (Region I), the transition region from GS lasing to two-state lasing (Region II) and the two-state lasing region (Region III) are compared and analyzed. It is found that the overshooting power and settling time in both Regions I and III decrease as the bias current increases. However, there exist abnormal behaviors of the overshooting power and settling time in Region II owing to the occurrence of ES lasing, which lead to fuzzy eye diagrams of the GS and ES lasing. Moreover, the ES lasing in Region III possesses much better eye diagrams because of its shorter settling time and smaller overshooting power over the GS lasing in Region I.

Ultrashort pulse and high power mode-locked laser with chirped InAs/InP quantum dot active layers

We demonstrate an ultrashort pulse and high power single-section mode-locked laser using chirped multiple InAs/InP quantum dot (QD) layers as the active region of the laser. The chirped QD active region consists of seven layers of InAs QDs of different heights, which is beneficial in broadening the material gain spectrum. A transform-limited Gaussian pulse with a pulse duration of 322 fs is obtained from a device of 1 mm in length. Moreover, the femtosecond pulse with highest peak power of 6.8 W is achieved for the 45.5-GHz mode-locked laser. These results show the potential of the mode-locked laser for femtosecond pulse generation with high peak power and high repetition rate in the 1.55-μm wavelength band.

Large Signal Modulation Characteristics in the Transition Regime for Two-State Lasing Quantum Dot Lasers*

Large-signal modulation capability, as an important performance indicator, is directly related to the high-speed optical communication technology involved. We experimentally and theoretically investigate the large-signal modulation characteristics of the simultaneous ground-state (GS) and the excited-state (ES) lasing in InAs/GaAs quantum dot laser diodes. The large-signal modulation capability of total light intensity in the transition regime from GS lasing to two-state lasing is unchanged as the bias-current increases. However, GS and ES large-signal eye diagrams show obvious variations during the transition. Relaxation oscillations and large-signal eye diagrams for GS, ES, and total light intensities are numerically simulated and analyzed in detail by using a rate-equation model. The findings show that a complementary relationship between the light intensities for GS and ES lasing exists in both the transition regime and the two-state lasing regime, leading to a much smaller overshooting power and a shorter settling time for the total light intensity. Therefore, the eye diagrams of GS or ES lasing are diffuse whereas those of total light intensity are constant as the bias-current increases in the transition regime.

Flat-topped ultrabroad stimulated emission from chirped InAs/InP quantum dot laser with spectral width of 92 nm

We demonstrate the generation of 92 nm (−3 dB bandwidth) flat-topped ultrabroad stimulation emission from a chirped InAs/InP quantum dot (QD) laser. A greatly enhanced bandwidth of the gain spectrum is achieved, which is attributed to the additionally broadened quantum dot energy levels utilizing gradually changed height of QDs in the stacked active layers. The laser exhibits a maximum output power of 0.35 W under pulsed conditions, and the average spectral power density of above 3.8 mW/nm is obtained. The ultrabroad lasing spectrum in the wavelength interval of 1.49–1.61 μm covering S-C-L bands makes such a laser potentially useful as an optical source for various applications being compatible with silica fibers.

Improved performance of 1.3-μm InAs/GaAs quantum dot lasers by direct Si doping

We demonstrate significantly enhanced performances of 1.3-μm InAs/GaAs quantum dot (QD) lasers by directly Si-doped QDs. The lasers were grown by molecular beam epitaxy. Following Si doping, the ridge waveguide laser, with uncoated facets, showed a remarkably reduced continuous-wave threshold current density of 71.6 A/cm2 (14.3 A/cm2 per QD layer), compared with 167.3 A/cm2 (33.5 A/cm2 per QD layer) for an undoped device with an identical structure, measured at 20 °C. Moreover, doping improved the single-side slope efficiency from 0.28 to 0.42 W/A. In addition, the Si-doped QD laser exhibited a higher lasing temperature of up to 140 °C compared with 120 °C for the undoped QD laser.

1.55-µm ultrashort pulse InAs/InP quantum dot mode-locked lasers with high output power

Summary form only given. We demonstrate an ultrashort pulse and high power single-section mode-locked laser using chirped multiple InAs /InP quantum dot (QD) layers as the active region of the laser. The chirped QD active region consists of seven layers of InAs QDs of different heights, which is beneficial in broadening the material gain spectrum. A transform-limited Gaussian pulse with pulse duration of 322 fs is obtained from a device of 1 mm in length. Moreover, the femtosecond pulses with peak power of as high as 6.8 W are achieved for the 45.5 GHz mode-locked laser. These results show the potential of the mode-locked laser for femtosecond pulse generation with high peak power and high repetition rate in the 1.55 μm wavelength band.

2004-nm Ridge-Waveguide Distributed Feedback Lasers With InGaAs Multi-Quantum Wells

Fabrication and characteristics of 2004-nm wavelength InP-based ridge-waveguide distributed feedback lasers with InGaAs multi-quantum wells are described. By means of a relatively simple fabrication process, the device can operate stably in a single mode without any mode hopping. A high side-mode suppression ratio of 49 dB is achieved. The emission wavelength can be finely controlled from 2000 to 2008 nm with a current-tuning rate of 0.0047 nm/mA and a temperature-tuning rate of 0.127 nm/K. In addition, the influence of facet coating conditions on the single-mode property of these distributed feedback lasers was investigated.