Recombination mechanisms in 1.3-/spl mu/m InAs quantum-dot lasers

We measure, in real units, the radiative and total current density in high performance 1.3-/spl mu/m InAs quantum-dot-laser structures. Despite very low threshold current densities, significant nonradiative recombination (/spl sim/80% of the total recombination) occurs at 300 K with an increasing fraction at higher current density and higher temperature. Two nonradiative processes are identified; the first increases approximately linearly with the radiative recombination while the second increases at a faster rate and is associated with the loss of carriers to either excited dot states or the wetting layer.     

Small-signal modulation characteristics of p-doped 1.1- and 1.3-/spl mu/m quantum-dot lasers

We have investigated the small-signal modulation characteristics of 1.1and 1.3-/spl mu/m p-doped quantum-dot lasers in order to evaluate the potential of acceptor doping. The maximum measured 3-dB bandwidth of the 1.1- and 1.3-/spl mu/m lasers are 11 and 8 GHz, respectively, which are only marginally higher than those in the corresponding undoped devices.     

Low-threshold GaInNAs single-quantum-well lasers with emission wavelength over 1.3 /spl mu/m

Low-threshold GaInNAs single-quantum-well (SQW) lasers with emission wavelength over 1.3 mum are demonstrated. Epitaxial layers of the lasers are grown using an aluminium-free gas-source molecular-beam epitaxy (GS-MBE) to prevent any impurity or contamination related to aluminium that might be incorporated into the GaInNAs active layer. The fabricated laser is believed it exhibit the lowest threshold-current density (200 A/cm²) among GaInNAs-SQW lasers grown by MBE. Moreover, record low threshold current (5.2 mA) and long-wavelength (1.31 mum) emission were achieved in a ridge-waveguide laser at 25degC under continuous-wave operation     

1.3-/spl mu/m InAs quantum-dot laser with high dot density and high uniformity

We realized a triple-stacked 1.3-/spl mu/m InAs quantum dot (QD) with a high density of 2.4/spl times/10/sup 11/ cm/sup -2/ and a high uniformity of below 24 meV that employs an As/sub 2/ source and a gradient composition (GC) strain-reducing layer (SRL) grown on a GaAs substrate. We demonstrated the 1.3-/spl mu/m wavelength emission of this triple-stacked QD laser with a 0.92-mm cavity length and a cleaved facet at room temperature. In addition, we realized the highest maximum modal gain yet reported of 8.1 cm/sup -1/ per QD layer at beyond 1.28 /spl mu/m by using our high-density and high-uniformity QD.     

Free-carrier effect on index change in 1.3 /spl mu/m quantum-dot lasers

Below threshold measurements of the carrier induced refractive index change in 1.3 /spl mu/m quantum-dot lasers at resonance and also below bandgap were carried out. It is demonstrated that free-carrier absorption contributes approximately half the total index change, and that its relative contribution is a function of device length. This result gives a lower bound to phase-amplitude coupling in quantum-dot lasers.     

High-frequency modulation characteristics of 1.3-/spl mu/m InGaAs quantum dot lasers

In this letter, we report results of small-signal modulation characteristics of self-assembled 1.3-/spl mu/m InGaAs-GaAs quantum dot (QD) lasers at room temperature. The narrow ridge-waveguide lasers were fabricated with multistack InGaAs self-assembled QDs in active region. A high characteristic temperature of T/sub o/=210 K with threshold current density of 200A/cm/sup 2/ was obtained. Small-signal modulation bandwidth of f/sub -3 dB/=12 GHz was measured at 300 K with differential gain of dg/dn/spl cong/2.4/spl times/10/sup -14/ cm/sup 2/ from detailed characteristics. We observed that a limitation of modulation bandwidth in high current injection appeared with gain saturation. This property can direct future high-speed QD laser design.     

Carrier distribution, gain, and lasing in 1.3-/spl mu/m InAs-InGaAs quantum-dot lasers

In this paper, we present the results of a theoretical model built to describe the temperature-dependent lasing characteristics of InAs-InGaAs quantum-dot (QD) lasers operating at 1.3 /spl mu/m. From the model, we find that traditional carrier distribution theories are inadequate to describe the performance of these lasers. We therefore introduce an improved model that allows for both free carriers and excitons in the dots. The new model provides threshold current and characteristic temperature T/sub 0/ values that are in good agreement with experimental data. The results of our modeling reveal that, while it is the excitons that mainly contribute to the gain, the ratio of excitons to free carriers significantly affect the T/sub 0/ of QD lasers. Our model results also indicate that the wetting layer current plays little role in QD laser performance. In addition, the model correctly predicts other experimental observations such as; increased T/sub 0/ for increased number of QD layers and p-doped structures, and the oscillatory behavior of T/sub 0/, lending further credibility to the model.     

Low-threshold proton-implanted 1.3-/spl mu/m vertical-cavity top-surface-emitting lasers with dielectric and wafer-bonded GaAs-AlAs Bragg mirrors

We demonstrate a new structure for long-wavelength (1.3-/spl mu/m) vertical-cavity top-surface-emitting lasers using proton implantation for current confinement. Wafer bonded GaAs-AlAs Bragg mirrors and dielectric mirrors are used for bottom and top mirrors, respectively. The gain medium of the lasers consists of nine strain-compensated AlGaInAs quantum wells. A record low room temperature pulsed threshold current density of 1.13 kA/cm/sup 2/ has been achieved for 15-/spl mu/m diameter devices with a threshold current of 2 mA. The side-mode-suppression-ratio is greater than 35 dB.     

High-performance three-layer 1.3-/spl mu/m InAs-GaAs quantum-dot lasers with very low continuous-wave room-temperature threshold currents

The combination of high-growth-temperature GaAs spacer layers and high-reflectivity (HR)-coated facets has been utilized to obtain low threshold currents and threshold current densities for 1.3-/spl mu/m multilayer InAs-GaAs quantum-dot lasers. A very low continuous-wave (CW) room-temperature threshold current of 1.5 mA and a threshold current density of 18.8 A/cm/sup 2/ are achieved for a three-layer device with a 1-mm HR/HR cavity. For a 2-mm cavity, the CW threshold current density is as low as 17 A/cm/sup 2/ for an HR/HR device. An output power as high as 100 mW is obtained for a device with HR/cleaved facets.     

Low-threshold continuous-wave 1.5-/spl mu/m GaInNAsSb lasers grown on GaAs

We present the first continuous-wave (CW) edge-emitting lasers at 1.5 /spl mu/m grown on GaAs by molecular beam epitaxy (MBE). These single quantum well (QW) devices show dramatic improvement in all areas of device performance as compared to previous reports. CW output powers as high as 140 mW (both facets) were obtained from 20 /spl mu/m /spl times/ 2450 /spl mu/m ridge-waveguide lasers possessing a threshold current density of 1.06 kA/cm/sup 2/, external quantum efficiency of 31%, and characteristic temperature T/sub 0/ of 139 K from 10/spl deg/C-60/spl deg/C. The lasing wavelength shifted 0.58 nm/K, resulting in CW laser action at 1.52 /spl mu/m at 70/spl deg/C. This is the first report of CW GaAs-based laser operation beyond 1.5 /spl mu/m. Evidence of Auger recombination and intervalence band absorption was found over the range of operation and prevented CW operation above 70/spl deg/C. Maximum CW output power was limited by insufficient thermal heatsinking; however, devices with a highly reflective (HR) coating applied to one facet produced 707 mW of pulsed output power limited by the laser driver. Similar CW output powers are expected with more sophisticated packaging and further optimization of the gain region. It is expected that such lasers will find application in next-generation optical networks as pump lasers for Raman amplifiers or doped fiber amplifiers, and could displace InP-based lasers for applications from 1.2 to 1.6 /spl mu/m.     

Coherence-collapse threshold of 1.3-/spl mu/m semiconductor DFB lasers

The onset of the coherence-collapse threshold is theoretically and experimentally studied for monomode 1.3-/spl mu/m antireflection/high reflection distributed-feedback lasers taking into account facet phase effects. The variation of the coherence collapse from chip to chip due to the facet phase is in the range of 7 dB and remains almost independent of the grating coefficient. Lasers that operate without coherence collapse under -15-dB optical feedback, while exhibiting an efficiency as high as 0.30 W/A, are demonstrated. Such lasers are adequate for 2.5 Gb/s isolator-free transmission without under the International Telecommunication Union recommended return loss.     

1.3 /spl mu/m InAs/GaAs multilayer quantum-dot laser with extremely low room-temperature threshold current density

A high growth temperature step used for the GaAs spacer layer is shown to significantly improve the performance of 1.3 /spl mu/m multilayer InAs/GaAs quantum-dot lasers. Extremely low room-temperature continuous-wave threshold current densities of 32.5 and 17 A/cm/sup 2/ are achieved for a three-layer device with as-cleaved facets and high-reflectivity coated facets, respectively.     

Optimization of material parameters in 1.3-/spl mu/m InGaAsN-GaAs lasers

We use a 10-band k/spl middot/p Hamiltonian to investigate gain characteristics of 1.3- /spl mu/m InGaAsN-GaAs 7-nm quantum-well lasers as a function of indium and nitrogen content. The parameters used were obtained by comparison with experimental transition energy data and fitting to measured spontaneous-emission line broadening. We conclude that optimum device performance is obtained by including the minimum amount of nitrogen necessary to prevent strain relaxation at the given well thickness.     

Bidirectional, subcarrier-multiplexed transmission using 1.3-/spl mu/m Fabry-Perot lasers

We demonstrate a full-duplex, subcarrier-multiplexed, transmission system which employs 1.3-/spl mu/m Fabry-Perot strained layer MQW laser diode transmitters in both directions. Coherent effects are reduced by using lasers with different mode spacing.     

Reliability analysis of AlGaInAs lasers at 1.3 /spl mu/m

Long-term reliability of 2.5 and 10 Gbit/s 1.3 /spl mu/m AlGaInAs lasers has been demonstrated. Analysis of accelerated life test predicts median life of /spl ges/1.57/spl times/10/sup 6/ h (180 years) at 85/spl deg/C.     

Time-domain modeling of mode suppression in 1.3-/spl mu/m Fabry-Perot lasers

Fabry-Perot lasers still comprise the bulk of lasers used in optical fiber systems. The spectral envelope, of the Fabry-Perot modes, can be modulated either deliberately or as a consequence of processing stages. This can be beneficial, in the case of modal sculpturing where specific Fabry-Perot modes are suppressed, or a hindrance in the case of poor devices. A time-domain model is used to model 1.3-/spl mu/m Fabry-Perot lasers. Simulated power conserving reflective sites are introduced between sections in the model to simulate the effect of reflective sites from etch pits on the output characteristics of real lasers. Spectral modulation of the laser output is reported in agreement with previous experimental results and the strength of reflections required is investigated. We also report the use of the model to investigate the effect of fiber dispersion on the modulated laser output with different spectral mode modulation.     

10 Gbit/s data modulation using 1.3 /spl mu/m InGaAs quantum dot lasers

Error-free 8 and 10 Gbit/s data modulation with quantum dot lasers emitting at 1.3 /spl mu/m is presented. 12 Gbit/s open eye patterns are observed. An integrated fibre-optic QD laser module yields error-free data modulation at 10 Gbit/s at a receiver power of -2 dBm.     

Modeling of the threshold operation of 1.3-/spl mu/m GaAs-based oxide-confined (InGa)As-GaAs quantum-dot vertical-cavity surface-emitting lasers

In the paper, the self-consistent optical-electrical-thermal-gain threshold model of the oxide-confined (OC) quantum-dot (QD) (InGa)As-GaAs vertical-cavity surface-emitting diode laser (VCSEL) is demonstrated. The model has been developed to enable better understanding of physics of an operation of GaAs-based OC QD VCSELs in a full complexity of many interactions in its volume between individual physical phenomena. In addition, the model has been applied to design and optimize the low-threshold long-wavelength 1.3-/spl mu/m GaAs-based OC QD VCSELs for the second-generation optical-fiber communication systems and to examine their anticipated room-temperature (RT) performance. An influence of many construction parameters on device RT lasing thresholds and mode selectivity has been investigated. Some essential design guidelines have been proposed to support efforts of technological centers in producing low-threshold single-mode RT devices.     

Optimisation of a-factor for quantum dot InAs/GaAs fabry-perot lasers emitting at 1.3 /spl mu/m

Dynamic measurements of the Henry factor alpha_H of InAs/GaAs Fabry-Perot lasers are compared for 3-, 5- and 10-QD layers. While alpha_H dramatically increases with the bias current for 3- and 5-QD stacks, it only amounts to <4 for the 10-layer stack at high currents, a value similar to that of QW-lasers