High performance quantum dot distributed feedback laser diodes around 1.15 μm

The effect of variation of the number of highly strained InGaAs quantum wells embedded in GaAs layers on the crystal quality of the epitaxial layers and AlGaAs/GaAs laser diodes was investigated. With four quantum wells and very thick waveguide layers, reasonable efficient laser diodes emitting above 1100 nm with a narrow vertical far field (FWHM = 15°) were obtained. Broad area laser diodes with 200 µm stripe width and an optimised doping profile emit nearly 20 W cw output power. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this paper we present an experimental analysis of the effect of RF modulation injection current in DFB and FP lasers nearthe first period doubling bifurcation (PDB). By increasing the amplitude of the modulation frequency at the onset of PDB thefirst results of a virtual Hopf phenomenon like behavior has been observed in both types of lasers. We characterized thisobservation by increasing the amplitude of the current modulation where two peaks appear in the spectrum, approaching oneto the other until fmally merging the onset of period doubling bifurcation as predicted by theory. The same virtual Hopfbehavior was observed when we set the amplitude modulation at a fixed value and we sweep the frequency modulation at theonset of the PDB point.Keywords: Laser Diode, Nonlinear Dynamics, Period Doubling Bifurcations. 1. INTRODUCTION Nonlinear dynamics in diode lasers has been the subject of many theoretical and experimental investigations in the lastdecade as they show a rich variety of irregular behavior in their route to chaos1. A single frequency diode laser is commonlystudied by a rate equation model which describes the time evolution of the photon and carrier densities. In these equations,the inclusion of an additional degree of freedom as modulation of the injection current, external light injection or opticalfeedback is needed for nonlinear dynamics to appear2.To our knowledge, the nonlinear behavior in semiconductor diode lasers has been extensively studied by many authors usingdelayed optical feedback and strong current modulation. In the former, the observed route to chaos was through successivesubharmonic bifurcations or by quasi periodic route3'4. In the strong current modulation case the period sequence wastruncated by period tripling before the onset of chaos5'6.On the other hand, the onset of a period doubling bifurcation point in many physical systems brings to nonlinear phenomenasuch as: 1) small signal amplification, 2) shift and suppression of the bifurcation point and 3) the emergence of a closelyspaced set of peaks in the frequency response7.In semiconductor lasers the parametric amplification was observed by Harth and co-workers8'9 which was analyzed byWiesenfeld few years after'°. In the study developed by Wiesenfeld in ref. 10, semiconductor lasers were proposed as goodcandidate to study the rich variety of nonlinear phenomena near period doubling bifurcations. A recent study has shown thatthe effect of Langevin noise in period doubling semiconductor lasers has a virtual Hopf ur12 previously predicted byWiesenfeld'34 as a virtual Hopf phenomenon in systems undergoing a period doubling bifurcations in the presence ofexternal noise.In the present study we have experimentally investigated the nonlinear dynamics of diode lasers in the period doublingbifurcation point. We study the influence of the amplitude modulation in Distributed Feedback (DFB) lasers near perioddoubling bifurcations. In Fabry-Perot (FP) lasers we performed as well the same study as DFB lasers and the analysis of thefrequency modulation near period doubling bifurcation. So in section II we described the experimental procedure for theonset of the first period doubling bifurcation performed in commercial DFB and FP InGaAsP diode lasers at 1,3 tm emission

High-power broad area lasers at 1180 nm were developed based on strained InGaAs quantum wells. The lasers feature a lifetime of more than 1200 h at 1 W and are believed to be a key component for the manufacturing of miniaturized laser modules in the yellow and orange spectrum by single-pass second harmonic generation to bridge the spectral region currently not accessible with direct emitting diode lasers. Future applications are laser cooling of sodium, high resolution glucose content measurements as well as spectroscopy on rare earth elements.

The fabrication of long-wavelength optoelectronic devices on GaAs substrates is an attractive method for monolithic integration of optical and electronic devices on a single chip for applications in telecommunications. In this letter we describe our studies of one such scheme using a novel structure for spatially separating a portion of the biaxial compressive stress due to lattice mismatch of the layers from the well layer, and demonstrate its feasibility. High quality pseudomorphic strained InGaAs quantum wells were grown on GaAs substrates by molecular beam epitaxy with a band edge between 1.3 and 1.4 μm at room temperature. Low-temperature photoluminescence spectroscopy as well as polarization-dependent absorption measurements in a waveguide geometry was used to characterize the structures.

Edge emitting diode lasers with highly strained InGaAs quantum wells and GaAs waveguide layers emitting at 1150 nm were investigated focusing on the impact of the waveguide design on the laser performance. Using a thick GaAs waveguide layer broad area devices with low vertical divergence of 20/spl deg/ FWHM and reliable operation at a power level of 80-mW//spl mu/m stripe width were demonstrated.

High-field mobility of light holes in strained InGaAs quantum wells

In this paper, we present the theoretical investigation of index-coupled distributed feedback (DFB) laser with tilted single mode ridge waveguides. By tilting part of the ridge waveguide in various degrees, DFB laser with manifold effective grating periods can be realized. The structure is analyzed using couple mode theory in matrix form based on threshold analysis. Important parameters of DFB laser like resonant frequency and threshold gains are obtained by solving the eigen-equation. The results indicate not only that the lasing frequency is modulated by the waveguide titling angle, but also large Gain Margin (GM) can be achieved at the threshold condition which enhance the stable single mode operation in index-coupled DFB laser.

For the fabrication of quantum dot (QD) distributed feedback (DFB) lasers, self-assembled InAs/InAlGaAs QDs were grown on the InP/InGaAs grating structures by a molecular beam epitaxy. Ridge-waveguide QD DFB lasers with a stripe width of 3 mum were fabricated. Single-mode lasing operation around the wavelength of 1.56 mum was successfully achieved under the pulsed and continuous-wave (CW) modes at room temperature. The lasing operation was also observed up to 70 degC under pulsed mode, which is the first observation on the single-mode lasing around 1.55 mum. The characteristic temperatures calculated from the temperature dependence of the threshold current density were 121.8 K from room temperature to 45 degC, which was reduced to 74.2 K from 45 degC to 70 degC.

Simulation and experimental investigation of the linewidth-power product of high power distributed feedback (DFB) diode lasers are presented. The reduction of linewidth-power product to 4.4 MHz.mW was observed for 780 nm DFB lasers.

A great improvement in the high-speed characteristics for compressively strained multi-quantum-well (MQW) distributed-feedback (DFB) lasers with self-aligned constricted mesa structures is described. Negative wavelength detuning is an important factor in making possible the extraction of potential advantages for the compressively strained MQW DFB lasers. A 17-GHz bandwidth, which is the highest among the 1.5- mu m MQW DFB lasers, is demonstrated. A wavelength chirp width of 0.42 nm at 10 Gb/s is obtained due to a reduced linewidth enhancement factor that has a magnitude of less than 2. Nonlinear damping K factor in a DFB laser with 45-nm negative detuning has drastically decreased to 0.13 ns, about half of that for unstrained MQW lasers. This is mainly due to an enhanced differential gain as large as 6.9*10/sup -12/ m/sup 3//s. The estimated intrinsic maximum bandwidth is 68 GHz. >

High-speed directly modulated distributed feedback (DFB) laser is crucial for high-speed optical communication systems. The modulation bandwidth and frequency chirp of such devices are primarily affected by the differential gain and linewidth enhancement factor (LEF) of the quantum wells (QWs) in the active region. In this work, the optical gain properties of long wavelength AlGaInAs-InP strained quantum wells (QWs) with different crystal orientations are numerically investigated using the multi-bands k.p theory, which considers both valence-band anisotropic and nonparabolicity. Compared to the QW laser grown on a conventional (001) substrate, a higher differential gain, and smaller LEF are observed for the laser grown on the (110) substrate with the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\rm{(\bar{1}10)}}$</tex-math></inline-formula> plane as the mirror facet. This is primarily due to the reduced effective mass of the valence band. The dynamic characteristics of (001)-and (110)-oriented DFB laser is theoretically studied using the one-dimensional traveling wave model (1D TWM) at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\rm{25}}\;^\circ \text{C}$</tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\rm{95}}\;^\circ \text{C}$</tex-math></inline-formula>. The simulation results show that the lower chirp and wider modulation bandwidth can be achieved for the QW laser grown on (110) substrate.

In-plane optical anisotropy was calculated for InGaAs strained quantum wells (QWs) with finite barrier potential on high-index (11n)-oriented GaAs substrates. The mixing effects of the spin–orbit split-off (SO) band were included by using 6 ×6 Hamiltonian based on the Luttinger–Kohn model. Calculated results reveal that optical anisotropy of the narrow QW is strongly dependent on barrier potential height, because the SO band mixing is enhanced by the strong confinement. Substrate off-angle dependence of photoluminescence intensity anisotropy observed in the (11n)A (n = 3, 4, and 5) In0.08Ga0.92As/GaAs strained QWs is well explained by the calculated curve with taking into account of the SO band mixing.

Single longitudinal mode (SLM) lasers are important tools for many scientific and commercial applications. SLM operation can be achieved in distributed-feedback (DFB) lasers based on Bragg structures. Semiconductor waveguide DFB lasers are well-established devices, but their output power is limited to a few hundred milliwatts. DFB lasers have also been demonstrated in dielectric waveguides. However, in this case the output power was even lower. Here we present the first monolithic Yb:YAG DFB laser. The waveguide and the DFB structure were fabricated in the volume of an Yb:YAG crystal by ultrafast laser inscription. The DFB laser delivered 2W of output power at a slope efficiency of 61% in SLM operation under pumping with an optically pumped semiconductor laser. This power level outperforms previously demonstrated dielectric DFB waveguide lasers by nearly an order of magnitude. Our approach paves the way for compact, robust, and highly efficient high-power SLM laser sources.

Semiconductor quantum cascade lasers (QCLs) that emit mid-infrared light in the wavelength range 4-9 μm are unipolar and the laser emission is due to intersubband transitions in a repeated stack of multiple quantum wells. The thermal management of these devices is a challenge. The overheating of the active region (referred to as “core” throughout this paper) in these lasers decreases the optical power and ultimately results in laser failure. In this paper, a detailed finite element-based numerical modeling of the thermal behavior of these devices as well as the measurements performed to validate the models are presented. The studies include the effect of submount material, mounting schemes such as epi-side down or epi-side up mounting, and, finally, the effect of core geometry on the thermal impedance. Various core designs, such as the split core, are analyzed. Various experiments were conducted to correlate the results with the numerical modeling by measuring the thermal impedance between the laser diode's core and the bottom of the substrate as well as the temperature change within a pulse of a distributed feedback (DFB) QCL which emits in a single longitudinal mode of narrow linewidth. The temperature of the active core of a DFB QCL can be determined by measuring the lasing frequency, which changes with the temperature of the active core. By measuring the lasing frequency as a function of time within a pump current pulse, the temperature change in the active core region can be determined and thereby thermal conductance of the laser structure. In the conclusion, various recommendations for efficient thermal performance of these QCLs are provided.

High-power spatially single-mode diode lasers at 1.4 - 1.5 μm wavelength are of interest as pump lasers for Raman and rare-earth doped fiber amplifiers as well as for material processing and for Light Detection and Ranging (LIDAR) at eye-safe wavelengths. A cost-efficient way to realize high-power high-brightness devices is the tapered resonator concept. We demonstrate InGaAsP/InP based diode lasers with compressively strained quantum wells and wavelengths around 1480 nm which were grown by solid source MBE. From broad area lasers with variations in quantum well number and waveguide layer thickness, parameters for the logarithmic gain model are deduced. With their implementation in 2-dimensional BPM simulations, an optimized resonator geometry is derived. Devices employ a 500 μm ridge section followed by a 2000 μm taper section with 6° angle. Continuous-wave (cw) output powers reach more than 1.5 W. Beam quality is characterized in terms of near field and far field distribution, M2, and astigmatism. An excellent agreement is found between measurement and simulation. For narrow-linewidth operation, devices are provided with anti-reflection coatings on both facets and spectrally stabilized with an external grating. We achieve 0.7 W single mode power and a side mode suppression ratio (SMSR) of 42 dB. Reliability is tested in terms of facet stability and lifetime. Pulsed measurements reveal a power stability up to more than 5 MW/cm2. From cw aging tests at 1 W output power, lifetimes of about 6,000 h are extrapolated.