Rozenn Piron

Spectral Analysis of 1.55-

In this paper, a theoretical model is used to investigate the lasing spectrum properties of InAs-InP(113)B quantum dot (QD) lasers emitting at 1.55 mum. The numerical model is based on a multipopulation rate equations analysis. Calculations take into account the QD size dispersion as well as the temperature dependence through both the inhomogeneous and the homogeneous broadenings. This paper demonstrates that the model is capable of reproducing the spectral behavior of InAs-InP QD lasers. Especially, this study aims to highlight the transition of the lasing wavelength from the ground state (GS) to the excited state (ES). In order to understand how the QD laser turns on, calculated optical spectra are determined for different cavity lengths and compared to experimental ones. Unlike InAs-GaAs QD lasers emitting at 1.3 mum, it is shown that a continuous transition from the GS to the ES is exhibited because of the large inhomogeneous broadening comparable to the GS and ES lasing energy difference.

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Dynamic properties of truly three-dimensional-confined InAs∕InP quantum dot (QD) lasers obtained by molecular beam epitaxy growth on a (311)B oriented substrate are reported. The relative intensity noise and small signal modulation bandwidth experiments evidence maximum relaxation frequency of 3.8GHz with a clear relaxation oscillation peak, indicating less damping than InAs∕GaAs QD lasers. The Henry factor amounts to ∼1.8 below threshold and increases to ∼6 above threshold, which is attributed to band filling of the thick wetting layer.

m InAs–InP(113)B Quantum-Dot Lasers Based on a Multipopulation Rate Equations Model

This article reports the improvement of broad area lasers epitaxially grown on InP(311)B substrate. Thanks to optimized growth techniques, a high density of uniformly sized InAs quantum dots (QDs) up to 1011 cm-2 is obtained. The device, which contains only two stacks of QDs, exhibits a ground state laser emission at 1.54 µm at room temperature associated with a threshold current density as low as 170 A/cm2. Experimental results also demonstrate a modal gain greater than 8 cm-1 per QD plane.

Dynamic properties of InAs∕InP (311)B quantum dot Fabry–Perot lasers emitting at 1.52μm

This paper reports on the tolerance of low-dimensional InAs/InP quantum-dash- and quantum-dot-based semiconductor lasers to optical feedback in the 1.55 mum window. For this purpose, the onset of coherence collapse (CC) is experimentally determined and systematically investigated as a function of different laser parameters, such as the injection current, differential gain, temperature, and photon lifetime. It is in particular found that for both material systems the onset of CC increases with the injection current in a similar way to bulk or quantum-well-based devices. Of most importance, we experimentally show that the differential gain plays a key role in the optical feedback tolerance. It is indeed shown to determine not only the range of the onset of CC but also the dependence of this threshold both on the temperature and laser cavity length. Increasing the operating temperature from 25degC to 85degC leads to a decrease of the onset of CC by a factor of only ~3 dB, well accounted for by the variation of the differential gain in this temperature range. We find no difference in the tolerance to external reflections of a truly 3-D confined quantum-dot-based laser and a quantum dash device of the same cavity length, which have similar differential gains. A tentative analysis of our data is finally carried out, based on existing models.

Demonstration of a Low Threshold Current in 1.54 µm InAs/InP(311)B Quantum Dot Laser with Reduced Quantum Dot Stacks

InAs quantum dash (QDH) and quantum dot (QD) lasers grown by molecular beam epitaxy on InP substrate are studied. The laser active zones with multiple stacked layers exhibit lasing wavelength at 1.55μm. On these devices, the experimental threshold current density reaches its minimum value for a double stacked QDH/QD structure. Other basic laser properties such as gain and quantum efficiency are compared. QD lasers exhibit better threshold current densities but equivalent modal gain per layer than QDH. Finally, the analysis of the modal gain on QD lasers shows a promising potential for improvement.

Optical Feedback Tolerance of Quantum-Dot- and Quantum-Dash-Based Semiconductor Lasers Operating at 1.55

The threshold current and its radiative component in 1.5μm InAs∕InP (311)B quantum dot lasers are measured as a function of the temperature. Despite an almost temperature insensitive radiative current, the threshold current increases steeply with temperature leading to a characteristic temperature T0≈55K around 290K. Direct observation of spontaneous emission from the wetting layer shows that some leakage from the dots to the wetting layer occurs in these devices. However, a decrease in the threshold current as a function of pressure is also measured suggesting that Auger recombination dominates the nonradiative current and temperature sensitivity of these devices.

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InAs quantum dot lasers grown on (311)B InP substrates with AlGalnAs barriers have been fabricated and studied. A large decrease of the threshold current with temperature was observed from 110 to 140 K. In the same temperature range, electroluminescence spectra showed a shape change, an energy shift with temperature, which can not be fitted with a Varshni law, and a large decrease of the laser linewidth. These results can be related to a delayed thermalization of carriers within quantum dot ensemble.

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We report on the uniformity improvement of InAs quantum dashes (QDHs) grown by molecular beam epitaxy on InP (100) through optimizing double cap technique. Broad-area lasers were fabricated with an emission wavelength of 1.58 μm. A threshold current density of 360 A/cm2 was achieved for a five stack QDH structure and a cavity length of 1.2 mm. This results from a reduced inhomogeneous broadening (62 meV) and lower internal optical losses (7 cm−1). The achievement paves the way toward ultralow threshold semiconductor laser for telecommunications.

Study of the characteristics of 1.55μm quantum dash/dot semiconductor lasers on InP substrate

This paper reports recent results on InAs/InP quantum dash–based, two-section, passively mode-locked lasers pulsing at 41 GHz and 10.6 GHz and emitting at 1.59 μm at 20 °C. The 41-GHz device (1 mm long) starts lasing at 25 mA under uniform injection and the 10.6 GHz (4 mm long) at 71 mA. Their output pulses are significantly chirped. The 41-GHz laser exhibits 7 ps pulses after propagation in 60 m of a single-mode fiber. The 10.6-GHz laser generates one picosecond pulses with 545 m of a single-mode fiber. Its single side-band phase noise does not exceed –80 dBc/Hz at 100 kHz offset, leading to an average timing jitter of 800 fs.

Temperature and pressure dependence of the recombination processes in 1.5μm InAs∕InP (311)B quantum dot lasers

InAs quantum dot (QD) formation on InP(001) has been investigated by gas source molecular beam epitaxy as a function of the substrate misorientation, arsenic pressure and temperature. A large improvement on quantum dot shape and density was obtained thanks to the use of substrates misoriented toward the [110] direction and low arsine flow rate. Round-shaped small QDs (diameter: 26 nm) in high density (9×1010 QDs/cm2) have been achieved using optimized growth conditions. Room temperature laser emission around 1.55 µm from was obtained with a threshold current density of 1 kA/cm2 for 1 mm long cavity.