Lasing characteristics of low-threshold oxide confinementInGaAs-GaAlAs vertical-cavity surface-emitting lasers

Some lasing characteristics of index-guided InGaAs-GaAlAs vertical-cavity surface-emitting lasers (VCSEL's) with a native oxide confinement structure, which produced a low threshold current of 70 μA, are presented. It was found that nonradiative recombination was reduced and the estimated surface recombination velocity was almost negligible. The oxidation process was uniform to produce low threshold devices while the oxidation rate was dependent on the doping or composition of DBR's     

Transverse mode selection in large-area oxide-confinedvertical-cavity surface-emitting lasers using a shallow surface relief

Transverse mode selection has been introduced in a large area oxide-confined vertical-cavity surface-emitting laser (VCSEL) by etching a shallow (only 40-nm deep) surface relief. The circular relief pattern, intended for fundamental mode selection, selects low order modes, resulting in significantly reduced beam divergence (from 48° to 13° and less over the entire drive current range) and improved spectral purity (width of emission spectrum reduced from 5 to less than 0.3 nm) compared to VCSEL's without surface relief. A maximum output power of 10 mW was measured     

Threshold analysis of vertical-cavity surface-emitting lasers with intracavity contacts

A numerical analysis of vertical-cavity surface-emitting lasers (VCSELs) incorporating intracavity contacts and distributed Bragg reflectors (DBRs) is presented. The model considers polarization dependent reflection at the DBRs, current spreading, and nonuniform carrier density distribution self consistently. Analytic expressions for the current spreading and the corresponding series resistance for VCSELs incorporating intracavity contacts are derived. It is shown that current spreading strongly affects the lateral gain profile, the threshold current density, the transverse mode shape and the transverse mode discrimination through the creation of intracavity optical phase and gain apertures. The series resistance and the depth of the dip in the current density distribution are used as figures-of-merit to provide guidelines for device optimization, as illustrated by means of two examples of long wavelength VCSEL designs.     

Vertical-cavity surface-emitting lasers integrated onto siliconsubstrates by PdGe contacts

Vertical-cavity surface-emitting lasers (VCSELs) have been integrated onto an aluminium coated silicon substrate. The InGaAs top-emitting VCSELs were grown by molecular beam epitaxy and individual lasers were defined by high energy proton implantation. The substrate was removed by a new substrate removal process and the lasers were bonded to an aluminised silicon substrate using a Pd/Ge/InSn contact. Threshold currents below 5.5 mA and output powers of ~1 mW were obtained for 40 μm VCSELs bonded to Si     

Intracavity Raman lasers

Experimental and theoretical studies of intracavity Raman lasers are presented. Advantages of intracavity Raman lasers, particularly for low-emission cross section and broadly tunable vibronic gain media, are described. Experimental studies of a hydrogen gas Raman laser pumped inside the cavity of an alexandrite laser are presented. A theoretical model of the dynamics of a unidirectional intracavity Raman ring laser is developed and solved analytically. This model is adapted for simulation experiments     

Bow-tie surface-emitting lasers

We report a new design for surface emitting semiconductor lasers operating at 940 nm, incorporating a double-flare cavity, and distributed Bragg reflector (DBR) mirrors also providing surface emission. This design can take advantage of the modal behavior of the unstable resonator, and has shown very good mode control, with coherent emission from two facets in the same direction. We report preliminary performance results showing very promising characteristics including single-mode diffraction limited operation, and spectral behavior with 42 dB side-mode suppression. This design has exhibited promising results for increasing the current range between the lasing threshold and the filament threshold     

Band-structure engineering for low-threshold high-efficiency semiconductor lasers

It is shown that by using a strained-layer superlattice to form the active region of a quantum-well laser the threshold current can be reduced and Auger recombination and inter-valence band absorption can be effectively eliminated. The band-structure requirements are discussed generally and might be achieved by alternative methods.     

Rate-equation model for coupled-cavity surface-emitting lasers

We present a detailed theoretical study of a vertical-cavity surface-emitting laser (VCSEL) with two optically coupled, active cavities. The study is based on a rate-equation model written for carriers and photons under steady-state conditions. The model allows one to determine all the relevant parameters-carrier densities, gains, and output powers-starting from two input parameters: the injection currents in each cavity. The system of equations is solved for different operating regimes of the device and the results provided by the model are shown to be in very good qualitative and quantitative agreement with the experimental data.     

InGaAs vertical-cavity surface-emitting lasers

The authors give theoretical and experimental results for vertical-cavity surface-emitting lasers (VCSELs). The modeling is applied to the design of InGaAs VCSELs. A simple method to calculate the reflectivity of semiconductor stack mirrors with graded interfaces and compound metal/semiconductor stack mirrors is introduced. The theoretical predictions are compared to results from actual device measurements. A novel technique is introduced to determine material parameters: fabrication of in-plane lasers from VCSEL material. The procedure used to determine the optical mode in such an in-plane laser is described. Using the insight gained from modeling, the external efficiency was increased to >30% with a threshold current density of 1 kA/cm²     

Mid-IR vertical-cavity surface-emitting lasers

We theoretically investigate the feasibility and potential performance of optically and electrically pumped vertical-cavity surface-emitting lasers (VCSELs) emitting in the mid-IR spectral region. Our model includes spontaneous, stimulated, and nonradiative recombination, numerical dispersion relations and optical matrix elements from a multiband finite-element algorithm, carrier and lattice heating, three-dimensional heat flow, electrical injection, photon propagation, and diffraction. Each modeled structure consists of a distributed Bragg reflector (DBR) semiconductor bottom mirror, a λ, 2λ, or 3λ optical cavity incorporating the type-II active region, and a dielectric top mirror through which the output beam is emitted. The optically pumped VCSEL structure with a 10-μm-diameter spot is predicted to operate up to a heat-sink temperature of 250 K and to be capable of producing >2 mW of CW output power. Furthermore, by collimating the pump beam with a microlens array, gain-guided VCSEL arrays with output powers in the watt range should be attainable. Comparable powers and operating temperatures are predicted for patterned devices with electrical injection through annular contacts. By far the most attractive properties are expected for structures employing a type-II interband cascade active region with electron recycling. The simulation predicts single-element threshold currents of 150 μA at 200 K and 1.1 mA at 300 K and CW output powers of 4.7 and 1.2 mW, respectively     

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....     

Few-mode vertical-cavity surface-emitting lasers for space-division multiplexing

In order to choose the proper radius of oxide aperture for few-mode vertical-cavity surface-emitting lasers (VCSELs), the influences of oxide aperture size on the multi-transverse-mode behaviors are investigated in detail. By establishing the effective refractive index model to simulate VCSELs with different radii of oxide apertures, the wavelength and corresponding order of different modes are obtained. VCSELs with three kinds of oxide apertures are manufactured. Then the multi-transverse-mode spectra and near-field are measured. It is found that when the radius is between 1.5 and 4.5 μm, few-mode VCSELs can be implemented. The 2.5 μm VCSEL manufactured in this paper only emits LP01 mode and LP21 mode. Since the space distance between the two modes is 2 μm, it is expected to realize direct-modulation few-mode VCSELs by channel etching or ion implantation between the two modes.     

长波长GaInNAs垂直腔面发射激光器

新出现的直接跃迁GaInNAs与具有高反射率的AlAs／GaAs分布布拉格反射镜相结合构成了GaAs基长波长(1．3—1．6μm)垂直腔面发射激光器(VCSEL)，将成为光纤通信、光互联和光信息处理等的关键元件。本文从材料的选取、外延技术和GaInNAs VCSEL国外和国内的发展状况等方面对长波长GaInNAs VCSEL进行了综合阐述。     

Electrically gain-switched vertical-cavity surface-emitting lasers

The authors report electrical gain-switching of a packaged vertical-cavity surface-emitting laser (VCSEL). Pulse durations as short as 24 ps at repetition rates up to 2 GHz were obtained from a four-quantum-well GaAs/AlGaAs VCSEL, which emits 0.8 mW continuous wave power in a single mode at room temperature and has a current threshold of 5 mA. Simultaneous measurement of the optical spectrum showed an almost transform limited linewidth indicating ultralow chirp. Optical pumping with subpicosecond pulses of the same packaged devices, held at a constant electrical bias, yielded 22 ps pulses, in good agreement with the electrical pumping. Simple calculations show that the pulse duration obtained by gain-switching is limited by the design constraints necessary to operate the VCSEL continuous wave at room temperature with low-threshold current, high-quantum efficiency, and reasonable output power     

Design optimization for high-brightness surface-emitting photonic-crystal distributed-feedback lasers

A new time-domain Fourier-Galerkin (TDFG) theory is developed to simulate the near-field, far-field and spectral characteristics of surface-emitting photonic-crystal distributed-feedback (SE PCDFB) lasers. It is found that a properly-designed two-dimensional hexagonal or square-lattice grating should efficiently couple the output into a single SE mode that retains coherence for aperture diameters of up to /spl ap/1 mm. We identify lattice structures and precise conditions under which all components of the transverse electric or transverse magnetic polarized optical fields constructively interfere to produce a single-lobed, near-diffraction-limited circular output beam. The TDFG simulations predict that quantum efficiencies as high as 30% (60% if reflectors are built into the waveguide structure) should be attainable. A surprising conclusion is that diffractive coupling into the surface-emitting direction must be relatively weak, in order to assure selection of the desired symmetric in-phase mode. Furthermore, gain media with a moderate linewidth enhancement factor should produce the best SE PCDFB performance, whereas edge emitters nearly always benefit from a very small value.     

Spatially dependent noise model for vertical-cavity surface-emitting lasers

We present a comprehensive noise model for vertical-cavity surface-emitting lasers (VCSELs). The time-domain model accounts for the stochastic fluctuations in the local carrier density in the separate confinement heterostructure and quantum wells, and in the modal intensity and phase of both the internal and the out-coupled optical field. In this work, we consider these fluctuations to be caused by the temporal uncertainty of the processes that supply or consume carriers and photons, such as carrier diffusion and photons escaping the cavity, and the processes that create or annihilate carriers and photons, such as stimulated emission and absorption. The noise model is based on a deterministic quasithree-dimensional dynamic model that treats the carrier transport, heat generation and dissipation, and optical fields in the device. Langevin noise terms are derived and added to the rate equations in the numerical solution. The noise model is applied to simulate the noise characteristics of fundamental-mode stabilized VCSELs with a shallow, mode discriminating, surface relief. The relative intensity noise and frequency noise of the output are calculated. From the latter, the linewidth of the VCSEL can be estimated. The results are compared with those of conventional multimode VCSELs.     

Polarization characteristics of 850-nm vertical-cavity surface-emitting lasers with intracavity contacts and a rhomboidal oxide current aperture

The polarization characteristics of 850-nm vertical-cavity surface-emitting lasers (VCSELs) with intracavity contacts and a rhomboidal oxide current aperture are studied. It is found that radiation polarization is always directed along the minor diagonal of the rhomboidal aperture (along the [\(\overline 1 \) 10] direction) for all single-mode VCSELs. The numerical simulation of carrier transport does not reveal the significant anisotropy of carrier injection to the active region. Furthermore, an analysis of the spatial distribution of the fundamental mode for two orthogonal polarizations within an effective waveguide model shows close transverse optical-confinement factors. Optical loss anisotropy in the asymmetric microcavity and/or gain anisotropy in the strained active region are the most likely mechanisms responsible for fixing the polarization.     

Vertical-cavity surface-emitting lasers with integrated refractivemicrolenses

The fabrication and performance of a vertical cavity surface emitting laser array integrated with microlenses are reported. The lasers emit at 967 nm through the substrate with integral polyimide microlenses. This design reduces beam divergence and provides an integrated device that emits a nearly collimated beam for applications such as optical interconnects     

High-speed modulation of vertical-cavity surface-emitting lasers

The IM (intensity modulation) and FM (frequency modulation) characteristics of vertical-cavity surface-emitting lasers are studied. The laser has high FM efficiency and broad IM bandwidth (near 8 GHz) at a very low bias (4.5 mA). Five Gb/s pseudorandom direct intensity modulation of this laser with open eyes is demonstrated.<>     

Small-dimension power-efficient high-speed vertical-cavity surface-emitting lasers

Small-dimension power-efficient high-speed oxide-confined 980 nm vertical-cavity surface-emitting lasers (VCSELs) with record-high bandwidth/power-dissipation ratio of 12.5 GHz/mW have been demonstrated. The devices show a modulation bandwidth of 15 GHz at a bias current 0.9 mA, corresponding to only 1.2 mW power dissipation