Effect of inhomogeneous line broadening on gain and differential gain of quantum dot lasers

Detailed theoretical analysis of the size fluctuation in InAs-GaAs quantum dot (QD) lasers is presented. Analytical expressions for the inhomogeneous line broadening and the optical gain are derived for a Gaussian size fluctuation distribution. The effect of size fluctuations on the QD carrier density, modal gain, and differential gain is studied. Red shifts in the gain peak is observed when size fluctuations increases. The energy detuning between the gain peak and the differential gain peak for a pyramidal quantum dot system having an average base length of 130 /spl Aring/ and standard deviation of 7 /spl Aring/ is about 12 meV.     

Vertical-external-cavity surface-emitting lasers and quantum dot lasers

The use of cavity to manipulate photon emission of quantum dots (QDs) has been opening unprecedented opportunities for realizing quantum functional nanophotonic devices and quantum information devices....     

Colliding-pulse modelocked quantum dot lasers

Colliding pulse modelocking is demonstrated for the first time in quantum dot lasers. Using 3.9 mm-long devices with a 245 /spl mu/m-long central absorber, 7 ps pulses at a repetition rate of 20 GHz is obtained. For Gaussian pulses a time-bandwidth product close to the Fourier transform limit is determined. These results confirm the potential of quantum dot lasers for high repetition rate harmonic modelocking.     

Nonlinear gain effects on spectral dynamics in quantum well lasers

A theoretical analysis is presented to show how nonlinear gain affects the spectral dynamics of quantum well (QW) lasers. The results indicate that the nonlinear gain, which is enhanced by the quantum confinement of carriers, causes an increase in the linewidth enhancement factor alpha . This enhancement of alpha results in spectral rebroadening: under high power output conditions. These properties should be taken into account when quantum well lasers are designed for highly coherent lasers.<>     

Advances in self-assembled semiconductor quantum dot lasers

In the past 20 years the semiconductor laser has become a key device in optical electronics because of its pure output spectrum and high quantum efficiency. As the capabilities of laser diodes have grown, so has the range of applications contemplated for them. A great success in semiconductor lasers has been brought by the ability to artificially structure new materials on an atomic scale by using advanced crystal growth methods such as MBE and MOVPE. The laser performance successes gained using quantum wells in optoelectronic devices can be extended by adopting quantum wire and quantum dot structures. There have been several reports of successful lasing action in semiconductor dot structures within the past few years. In this article I will briefly review the recent progress in the development of quantum dot lasers.     

Relaxation oscillations of quantum dot lasers

The relaxation oscillation frequency of quantum dot lasers is modelled theoretically. Its dependency on the driving current, maximum gain, intersublevel relaxation time and homogeneous broadening is investigated. For suitable, feasible quantum dot laser parameters, relaxation oscillation frequencies up to 10 GHz are predicted. Making these devices useful for 5 Gbit/s communication systems     

Design of tunneling injection quantum dot lasers

In recent years, semiconductor quantum dot (QD) lasers have attracted considerable attention due to their potentia applications[1]. Although QD laser has been predicted can have more excellent performance than conventional quan- tum well laser, so far tem…     

Low chirp observed in directly modulated quantum dot lasers

We have examined the dynamic properties of high-aspect-ratio InAs-quantum-dot (QD) lasers at room temperature. A novel characteristic of low chirp in the lasing wavelength under 1-GHz current modulation was found in the quantum dot lasers. This is more than one order of magnitude less than the typical chirp (0.2-nm) found in a conventional quantum well laser that we used as a reference. Low chirp was obtained not only in the ground state lasing but in the second level lasing of quantum dots as well.     

High-performance 980 nm quantum dot lasers for high-powerapplications

High-performance quantum dot lasers emitting at 980 nm with output powers of up to 4 W CW from a single facet (AR/HR coating, 100 μm stripe width) have been fabricated. Wall-plug efficiencies >50%, were achieved at room temperature. Owing to an improved carrier confinement output powers as high as 1 W CW can be obtained from the fundamental dot transition even at temperatures as high as 110°C     

High-power 980 nm quantum dot broad area lasers

High-power quantum dot broad area lasers emitting at 980 nm are presented. Continuous-wave output powers of 4.3 W from a 50 /spl mu/m stripe width laser and of 6.3 W from a 100 /spl mu/m stripe width laser were achieved at 15/spl deg/C     

Differential gain in bulk and quantum well diode lasers

Differential gain (g^') of bulk and single-quantum-well (SQW) lasers was determined from threshold current density and differential quantum efficiency measurements. The threshold measurement technique was used to show that g^' is a function of cavity length (L) in SQW lasers and independent of L in bulk lasers. It was found that g^' of long SQW lasers (1000 μm) is about 7×10^-16 cm² , approximately two times that of bulk lasers. At short cavity lengths (250 μm), g^' is about the same for both laser types     

Differential optical gain in a GaInN/AlGaN quantum dot

Electronic and optical properties are obtained with the increase in indium alloy content (x) in a Ga_1-xIn_xN/Al_0.2Ga_0.8N quantum dot. The barrier height with the different In alloy contents is applied to acquire the confinement potentials. The results are obtained taking into consideration geometrical confinement effect. The optical absorption coefficient with the photon energy is observed in a Ga_1-xIn_xN/Al_0.2Ga_0.8N quantum dot. The optical output with the injection current density and the threshold optical pump intensity for various In alloy contents are studied. The differential gain as functions of indium alloy content, charge density and the dot radii in the Ga_1-xIn_xN/Al_0.2Ga_0.8N quantum dot are investigated. The exciton binding energy is calculated in order to obtain the exciton density, the optical gain and the threshold current density in the Ga_1-xIn_xN/Al_0.2In_0.8N quantum dot. The results show that the red shift energy with an increase in In alloy content is found and the differential gain increases with the charge carrier density.     

Theory of threshold characteristics of semiconductor quantum dot lasers

A comprehensive theory of threshold characteristics of quantum dot (QD) lasers, which provides a basis for optimization of their design, is reviewed. The dependences of the gain, transparency current, threshold current, characteristic temperature, and multimode generation threshold on the parameters of the QD ensemble (surface density and size dispersion of QDs), cavity (stripe length and thickness of the waveguide region), heterocontacts (band offsets), and temperature are considered in detail. The limiting characteristics of the laser (optimum structure parameters, minimum threshold current density, and characteristic temperature of the optimized structure) are discussed at length. The results of the analysis may serve as direct recommendations for the development of QD lasers that significantly outperform the semiconductor lasers currently in use.     

Low-threshold quantum dot lasers with 201 nm tuning range

A grating-coupled external-cavity quantum dot laser is tuned across a 201 nm range at a maximum bias of 2.87 kA/cm². One order of magnitude less than the bias required for comparable tuning of quantum well lasers. The tuning range increases for higher cavity losses of the quantum dot laser     

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.     

InAs/InP量子点激光器制备工艺研究

报道了通过化学湿刻蚀制备窄脊条InAs/InP量子点激光器的方法。激光器脊条主要是由半导体材料InGaAs和InP构成,通过选择合适配比的H2SO4∶H2O2∶H2O和H3PO4∶HCl腐蚀溶液和InP的腐蚀方向,在室温下选择性地腐蚀了InGaAs和InP,获得了窄脊条宽为6μm的量子点激光器。此激光器能够在室温连续波模式下工作,激射波长在光纤通信重要窗口1.55μm,单面最大输出功率超过12mW。     

Inhomogeneous broadening of the ground electron level in a quantum dot array

The connection between the size and shape distribution of quantum dots (QDs) and the density of electron states is analyzed. It is shown that, in an array of nonidentical QDs, the density of states in the vicinity of the ground level takes the form of an asymmetric peak whose shape and position are determined by the statistical parameters of the array (equilibrium radius, as well as variance and asymmetry of the size distribution of the QDs). General relationships between these parameters and the shape of the peak are determined.     

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.     

Features of simultaneous ground- and excited-state lasing in quantum dot lasers

The lasing spectra and light-current (L-I) characteristics of an InAs/InGaAs quantum dot laser emitting in the simultaneous lasing mode at the ground- and excited-state optical transitions are studied. Lasing and spontaneous emission spectra are compared. It is shown that ground-state quenching of lasing is observed even in the absence of active region self-heating or an increase in homogeneous broadening with growth in the current density. It is found that the intensities of both lasing and spontaneous emission at the ground-state transition begin to decrease at a pump intensity that significantly exceeds the two-level lasing threshold. It is also found that different groups of quantum dots are involved in ground- and excited-state lasing.