Linewidth enhancement factor in strained quantum well lasers

The linewidth enhancement factor α of strained quantum-well lasers is analyzed by the k-p perturbation method using the effective-mass approximation. It is found that the α factor in a strained In_0.80Ga_0.20As/InP quantum-well (QW) laser with 1.9% biaxial compression is less than 1.5. For a strained QW laser with p-type modulation doping (MD) of 5×10 ¹⁸ cm^-3, the α factor is as small as 0.8. It is also demonstrated that the spectral linewidth and wavelength chirping in the strained MD QW laser are significantly less than those in conventional bulk and QW lasers     

Linewidth enhancement factor for quantum-well lasers

The linewidth enhancement factor ? is calculated for an idealised GaInAs quantum-well laser. Values between 1 and 2 are found for a range of possible lasing energies. Somewhat larger values are expected for GaInAs quantum wells with InP barriers. It is concluded that dramatic reductions in ? are not to be expected for quantum wells.     

Linewidth enhancement factor and nonlinear gain in ZnSesemiconductor lasers

We have investigated the effects of the Coulomb interaction on the optical gain and the refractive index of ZnSe semiconductor lasers. The Coulomb interaction increases the differential gain, leading to a decrease of the threshold carrier density. Its influence on the linewidth enhancement factor and the nonlinear gain coefficient is relatively small because it increases both the gain and the refractive index simultaneously. We have compared the linewidth enhancement factor α and the nonlinear gain coefficient ϵ for ZnSe and GaAs lasers with the effects of the Coulomb interaction taken into account. For typical values of total cavity losses, the values of α and ϵ are higher for ZnSe lasers compared with GaAs lasers     

GaAs基量子级联激光器材料结构设计的进展

GaAs基量子级联激光器的出现,在器件的设计制作和处理工艺上开辟了有意义的前景。本文概述了近年来GaAs基量子级联激光器在波导核心层、波导以及光学谐振腔方面设计的原理、进展,并介绍了一些新颖的结构。     

Linewidth enhancement factor of 1.3 mu m InGaAsP/InP strained-layer multiple-quantum-well DFB lasers

The linewidth enhancement factor alpha in a 1.3 mu m InGaAsP/InP strained-layer multiple-quantum-well (SL-MQW) distributed feedback (DFB) laser has been evaluated from the relation between the frequency and intensity modulation indexes, and the spontaneous emission spectra below threshold current. It is demonstrated that the measured alpha -parameter of a 1.3 mu m SL-MQW DFB laser is about two, and is much smaller than that in a conventional bulk DFB laser. From the resonance frequency dependence on the output power, it is concluded that this reduction of the alpha -parameter originates in the increased differential gain. The reduction of wavelength chirping, as a result the low alpha -parameter, was experimentally confirmed for the SL-MQW DFB laser.<>     

High-performance quantum cascade lasers with electric-field-freeundoped superlattice

An optimized design of quantum cascade lasers with electric field free undoped superlattice active regions is presented. In these structures the superlattice is engineered so that: (1) the first two extended states of the upper miniband are separated by an optical phonon to avoid phonon bottleneck effects and concentrate the injected electron density in the lower state and (2) the oscillator strength of the laser transition is maximized. The injectors' doping profile is also optimized by concentrating the doping in a single quantum well to reduce the electron density in the active material. These design changes result in major improvements of the pulse/continuous-wave performance such as a weak temperature dependence of threshold (T₀=167 K), high peak powers (100-200 mW at 300 K) and higher CW operating temperatures for devices emitting around at λ~8.5 μm     

Linewidth study of InAs-InGaAs quantum dot distributed feedback lasers

The linewidth of laterally loss-coupled distributed feedback (DFB) lasers based on InAs quantum dots (QDs) embedded in an InGaAs quantum well (QW) is investigated. Narrow linewidth operation of QD devices is demonstrated. A linewidth-power product less than 1.2 MHz /spl middot/ mW is achieved in a device of 300-/spl mu/m cavity length for an output power up to 2 mW. Depending on the gain offset of the DFB modes from the QD ground state gain peak, linewidth rebroadening or a floor is observed at a cavity photon density of about 1.2-2.4/spl times/10/sup 15/ cm/sup -3/, which is much lower than in QW lasers. This phenomenon is attributed to the enhanced gain compression observed in QDs.     

Chemical sensors based on quantum cascade lasers

There is an increasing need in many chemical sensing applications ranging from industrial process control to environmental science and medical diagnostics for fast, sensitive, and selective gas detection based on laser spectroscopy. The recent availability of novel pulsed and CW quantum cascade distributed feedback (QC-DFB) lasers as mid-infrared spectroscopic sources address this need. A number of spectroscopic techniques have been demonstrated worldwide by several groups. For example, the authors have employed QC-DFB lasers for the monitoring and quantification of several trace gases and isotopic species in ambient air at ppmv and ppbv levels by means of direct absorption, wavelength modulation, and cavity enhanced and cavity ringdown spectroscopy     

Dependence of linewidth enhancement factor on crystal orientationin strained quantum well lasers

The linewidth enhancement factor a in strained quantum well (QW) lasers is estimated theoretically for various crystallographic directions. It is found that the a factor in a strained In_0.7Ga_0.3As-InP QW laser on a (111) substrate is less than 1.4, much lower than for conventional strained QW lasers on (001) substrates     

GaAs-based quantum cascade lasers with native oxide-defined currentconfinement

The development of broad area (width ≈100 μm) GaAs-based quantum cascade lasers (QCLs) with 20 μm-wide current apertures defined by selective oxidation of the Al_0.9Ga_0.1As optical cladding layers is reported. Processing the lasers in this way enhances heat removal from the active region of the structure, allowing improved pulsed performance at higher duty cycles compared with conventional ridge waveguide structures     

Linewidth enhancement factor of vertical-cavity surface-emittinglaser diodes

The linewidth enhancement factor α characterizes the performance of semiconductor lasers, such as spectral linewidth broadening for CW operation and wavelength chirping under high-frequency modulation. We have for the first time determined the α factor of vertical-cavity surface-emitting lasers from the measured linewidth-power product and more precisely from the frequency to amplitude modulation ratio at high-frequency current modulation. Both methods provide the same α factor of 3.7. The minimum linewidth was as narrow as 70 MHz and the linewidth-power product was 5.4 MHz·mW neglecting the residual linewidth     

Improved CW operation of quantum cascade lasers with epitaxial-sideheat-sinking

First results on the epilayer-side mounting of quantum cascade (QC) lasers are presented. Operated in continuous-wave (CW) mode, these lasers are superior to substrate-bonded devices. The maximum CW temperature is raised by 20 K (up to 175 K), and, at comparable heat sink temperatures, the performance with respect to threshold current, output power, and slope efficiency is greatly improved for the epilayer-side mounted devices. QC-laser-specific mounting procedures are discussed in this letter, such as the high reflectivity coating of the back-facet and the front-facet cleaving after mounting. Modeling of the temperature distribution inside the QC laser shows a strong temperature gradient within the active waveguide core, which partly explains the still low maximum CW operating temperatures     

Spectral dependence of the linewidth enhancement factor in quantum dot lasers

The spectral analysis of amplified spontaneous emission is used to determine the linewidth enhancement factor (α-factor) in lasers based on InAs/InGaAs quantum dots (QDs) in a wide spectral range near the ground-state optical transition energy. The effect of the pump current and number of QDs on the spectral dependences of the α-factor is examined. The temperature dependence of the spectra of the α-factor is experimentally determined for the first time for lasers with InAs/InGaAs QDs. An explanation is suggested for the observed anomalous decrease in the α-factor with increasing temperature.     

Continuous-wave operation of GaInAs-AlGaAsSb quantum cascade lasers

We report on the demonstration of continuous-wave (CW) operation of GaInAs-AlGaAsSb quantum cascade (QC) lasers. By placing a 2.5-/spl mu/m-thick gold layer on both sides of the laser ridge to extract heat from the active region in the lateral direction, together with mounting the device epilayer down, we have achieved CW operation of GaInAs-AlGaAsSb QC lasers composed of 25 stages of active/injection regions. The maximum CW operating temperature of the lasers is 94 K, and the emission wavelength is around /spl lambda//spl sim/4.65 /spl mu/m. For a device with the size of 10/spl times/2000 /spl mu/m/sup 2/, the CW optical output power per facet is 13 mW at 42 K and 4 mW at 94 K. The CW threshold current density is 1.99 kA/cm/sup 2/ at 42 K, and 2.08 kA/cm/sup 2/ at 94 K, respectively.     

Stability of pulse emission and enhancement of intracavity second-harmonic generation in self-mode-locked quantum cascade lasers

We report the observation of stable pulse emission and enhancement of intracavity second-harmonic generation (SHG) in self-mode-locked quantum cascade (QC) lasers. Down-conversion of the detector signal by heterodyning with an RF signal allows the direct observation of the pulsed laser emission in the time domain and reveals a stable train of pulses characteristic of mode-locked lasers. The onset of self-mode locking in QC lasers with built-in optical nonlinearity results in a significant increase of the SHG signal. A pulse duration of /spl sim/12 ps is estimated from the measured increase of the SHG signal in pulsed emission compared to the power expected for the SHG signal in CW emission. This value is in good agreement with the pulse duration deduced from the optical spectral width.     

Linewidth enhancement factor and near-field pattern in tunnel injection In/sub 0.4/Ga/sub 0.6/As self-assembled quantum dot lasers

Measurements of ultra-low linewidth enhancement factor in ridge-waveguide tunnel injection In/sub 0.4/Ga/sub 0.6/As/GaAs self-assembled quantum dot lasers have been made and the results compared with similar quantum well lasers. Values of /spl alpha//spl sim/3.8 were measured in the quantum well lasers, and /spl alpha/ was /spl les/0.7 in the quantum dot lasers. The consequent suppression of filamentation in the quantum dot devices has also been observed.     

Dependence of linewidth enhancement factor ? on waveguide structure in semiconductor lasers

In semiconductor lasers, the ratio ? of the real part to the imaginary part of the change in refractive index due to the change in carrier density determines the magnitude of dynamic and static line broadenings. The letter reports that the effective value of ? depends on the structure of the waveguide, where both index and gain mechanisms induce transverse-mode guiding.     

High-power long-wavelength room-temperature MOVPE-grown quantum cascade lasers with air-semiconductor waveguide

Quantum cascade lasers grown by metal organic vapour phase epitaxy (MOVPE) with high peak output power of 1.3 W at 300 K emitting a wavelength of 9.8 mum are reported. The devices are processed in wide ridge waveguide structures with an air-semiconductor interface to confine the laser optical mode. This design increases the optical overlap factor and reduces waveguide losses.     

量子级联激光器的原理及研究进展

量子级联激光器的发明是半导体激光器领域里程碑的发展,开创了中远红外半导体激光的新领域,在红外对抗、毒品和爆炸物检测、环境污染监测、太赫兹成像等方向有广泛的应用前景.本文阐述了量子级联激光器的基本原理、以及材料和器件的研究,结合应用方向对其研究进展进行了综述性介绍.     

量子级联激光器的电路模型分析

通过分析量子级联激光器(QCL)中的电子在量子阱输运的单极行为,得到它的速率方程,以此为基础建立起它的等效电路模型,利用PSPICE进行电路模拟,得到了它的频率响应特性,并对可能影响它的调制特性的一些因素进行了分析.