A self-consistent model of the lateral behavior of a twin-stripe injection laser

A fully self-consistent computer model of the steady-state behavior of the zero-order lateral optical field of a GaAs twin-stripe injection laser is presented which takes into account current spreading in the p-type confining layer, the effect of lateral diffusion of carriers in the active layer, and bimolecular and stimulated radiative recombination. The results predict the lateral movement of the near field of the optical signal under asymmetric drive conditions, as observed in practice. Also calculated are the corresponding carrier and current density distributions. It is shown that the near-field zero order lateral optical field can be beam steered across the facet by only 2μm, typically. However, the initial position of the beam can be controlled by the two-stripe currents and also the geometry of the device. For the case whereI_{s1} approx I_{s2}the beam movement is seen to be proportional to eitherI_{s1}orI_{s2}. The results show that beam steering is not accompanied by a negative slope to theI-Lcharacteristics. The effect of geometry and diffusion coefficient on the value of maximum current allowed before modal instability occurs is also given.     

Analysis of lateral-mode behavior of twin-stripe lasers related tothe negative slope in their current-light characteristics

The lateral oscillation mode in twin-stripe lasers is analysed with the diffusion constant D in the active layer as a parameter. Characteristics of modal gain and optical intensity distribution vs. current are shown to be strongly dependent on the diffusion constant because the diffusion constant determines the depth of the dip in the carrier distribution. For certain values of D, results which are in good agreement with experimentally observed results were obtained. A negative slope appears in the curves of modal gain vs. current, and the optical field is in the weakly pumped side in the negative slope region. The condition for which the negative slope appears is determined     

A coupled-mode analysis of twin-stripe index-guided lasers

An approximated coupled-mode solution to the problem of lateral mode behavior in twin-stripe index-guided injection lasers near threshold is presented. The optical properties are determined by the coupling coefficients between the two waveguides, taking into account the external current-dependent perturbation to the dielectric constant. In the calculations of the external perturbation, a simple model of current spreading under the contacts and carrier diffusion in the active layer is given for a multistripe structure. Emphasis is on the influence of the current ratio on the lateral field shape and modal gain. It is shown that for symmetrical current injection, the fundamental supermode has a slight advantage (higher gain) over the second 180° phase-shifted mode. As the injected current ratio is driven away from the symmetrical point, the second supermode is favored with increasing modal gain difference. The coupled-mode approach is relatively simple and can describe rather accurately this already-known behavior     

Carrier density dependence of refractive index in AlGaAs semiconductor lasers

Carrier density dependence of the refractive index in the active layers of semiconductor lasers is evaluated from the wavelength shift with increases in current by taking into account effects of the active layer temperature rise and lateral carrier and optical field distributions on the wavelength shift. The derived refractive index change due to carrier density increase is-4 times 10^{-27}m³, which is in good agreement with the theoretical value.     

An Analytical Solution of the Lateral Current Spreading and Diffusion Problem in Narrow Oxide Stripe (GaAl)As/GaAs DH Lasers

An exact solution is presented to the problem of lateral current spreading in the resistive layer of oxide stripe geometry DH lasers. The two-dimensional Laplace equation was solved by conformal mapping using the Schwarz-Christoffel transformation. The diffusion equation containing nonlinear recombination terms was solved numerically. Computed examples demonstrate that the customary one-dimensioned treatment of the resistive layer or the assumption of constant current density under the stripe contact are not always justified, particularly for narrow stripe widths and low specific resistivities. This region of low values of the resistivity and stripe width, however, is of great practical interest in the design of oxide stripe lasers having high thermal stability and kink-free characteristics.     

Low-threshold (Ga,In)(As,P) d.h. lasers emitting at 1.55 ?m grown by l.p.e.

Threshold current densities as low as 2.13 kA cm?2 have been achieved in broad-contact double-heterostructure lasers with an emission wavelength of 1.55 ?m. The three-layer structure was grown by liquid-phase epitaxy and contained a quaternary active layer 0.6 ?m thick and a p-type quaternary upper confining layer with a bandgap of 1.05 eV. The normalised threshold current density was 3.5 kA cm?2 ?m?1.     

Self-consistent analysis of gain-guided triple stripe lasers

A considerable near field shift in DH triple stripe lasers is demonstrated by tailoring the applied bias on the stripes. No closed form solution for the current spreading in the passive layer is assumed. The two dimensional Laplace's equation in the passive layer, which is coupled with the diffusion equation of carriers in the active layer via the variation of the separation of quasi-Fermi levels, is solved consistently. Both the bimolecular and stimulated recombinations are included in the diffusion equation. The stimulated recombination determination couples the wave equation with the rest of the problem which is treated self-consistently. The paper highlights the influence of the different applied potentials on the stripes, the electrode spacing and the diffusion constant on the optical behaviour of the device.     

Self-Consistent Model and Numerical Analysis of VCSEL's Laser Diodes

A self-consistent model of vertical-cavity surface-emitting lasers (VCSEL's) is presented in this paper, in which the carrier diffusion rate equation, the photon density rate equation, and the thermal conduction equation are considered simultaneously. The nonuniform heat flux density distribution in the active region due to the current-spreading effect is taken into account. The effects of temperature on gain and transparency carrier density are also included in this model. It is nonlinearly and self-consistently solved in the Matlab environment. The transient and lateral distribution characteristics of the carrier and photon densities and the junction temperature are investigated. Some interesting results are gotten and analyzed.     

质量迁移层对InGaAsP BH半导体激光器阈值电流和模式行为的影响

用 Schwarz-Christoffel变换法计算了质量迁移InGaAsP BH激光器中的结电压分布;分析了迁移层和有源层侧向厚度,上限制层空穴浓度和有源层注入电流对迁移层同质结漏电流的影响;并提出以过渡模式为界,区分A类和B类模式,从理论上比较全面地分析了五层对称平板波导的模式行为;指出降低阈值电流和保证单基横模工作这两方面对迁移层厚度有相反的要求,从而存在一定意义下的最佳迁移层厚度.     

Near-field control in multistripe geometry injection lasers

Control of the intensity and position of the near field is demonstrated in an analysis of twin-stripe and triple-stripe injection lasers. Calculations of file electrooptical properties of the structures are presented, taking into account the interaction between the carrier concentration profile and the optical field. For twin-stripe devices interstripe coupling is investigated as a function of stripe separation. For stripe separation comparable with stripewidth, the properties of triple-stripe lasers become of interest. Nonlinear light-current characteristics for the twin-stripe device are obtained and lead to an interpretation of such characteristics in conventional stripe geometry lasers.     

Observation of switching related to bistability between twocross-coupled lateral modes in twin-stripe lasers

Switching between two cross-coupled lateral modes in gain-guided twin-stripe lasers has been experimentally observed with current injection of nominally identical pulses, which strongly indicates bistability. Near- and far-field patterns at both facets are presented, which clearly shows a skewed light field which couples from under one stripe to under the other. Cross-coupled mode operation was obtained only for relatively long cavity lasers, which is consistent with the theory for twin-stripe lasers with high interstripe gain     

Theoretical and experimental study of threshold characteristics in InGaAsP/InP DH lasers

Threshold characteristics of stripe-geometry InGaAsP/InP double-heterostructure injection lasers have been analytically derived as a function of active layer thickness and stripe width. The effects of stripe width, refractive index in the active layer, diffusion of injected carriers, carrier lifetime, absorption loss in the cladding layer, gain coefficient, and cavity length on the optimum thickness of the active layer which gives minimum threshold or on threshold current density were studied. These lasers were fabricated on     

Design of quantum well AlGaAs-GaAs stripe lasers for minimizationof threshold current-application to ridge structures

The gain saturation effect and the various leakage currents related to a strip structure (spreading current, lateral diffusion current, optical cavity recombination current, and Auger recombination current) are considered. The minimum threshold current (3.3 mA) is obtained with a multiquantum-well (MQW) structure (5×80 Å) at a cavity length of 80 μm. At these values, the lateral leakage current (spreading and lateral diffusion currents) represents about 50% of the threshold current. It is shown that for short-cavity lasers, the MQW is preferred to the SQW (single-quantum-well) structure. However, the well number in the active layer of a ridge structure is limited by the decrease of the parallel confinement and the increase of the lateral leakage current. Finally, good agreement was obtained in comparing the calculations with experimental results for GRINSCH (graded-index separate-confinement heterojunction) SQW lasers     

Submilliamp vertical-cavity surface-emitting lasers with buriedlateral-current confinement

Lateral current confinement of intracavity contacted 0.98 μm vertical cavity surface emitting lasers has been achieved by inserting a 50 nm thick n-type GaAs current blocking layer into the p-doped cladding. Epitaxial regrowth by solid source MBE is used to bury the current confining layer in the cavities. Threshold currents of 0.78 mA, optical output powers of 1 mW and external quantum efficiencies of up to 15% are measured. The lateral current injection via the top p-type cladding leads to low voltages at threshold of 1.78 V     

深扩Zn平面条形激光器作用层注入载流子空间分布的分析

本文分析了深扩Zn平面条形激光器作用层注入载流子的空间分布。从理论上阐明了深扩Zn平面条形激光器的注入电流在P-Al_xGa_(1-x)As限制层沿结平面方向的扩展可以忽略。因此,注入载流子在其作用层的空间分布比普通平面条形激光器窄得多,进而其增益波导也窄得多。从理论上证明的结论:轻掺杂或不掺杂作用层深扩Zn平面条形激光器的水平横模稳定的主要原因是其增益波导窄。     

Interstripe coupling and current spreading in a subthreshold double heterostructure twin stripe laser

TWin stripe laser structures show great promise in integrated optics Systems. It has been proposed that optical interactions in such Structures should produce properties such as beam steering, optical pulse generation and bistability. However, fundamental properties of these devices, including the effect of the resistive p-type cladding layer on the current density distribution injected into the active region, the terminal behavior of the device, and the effect of the stripe width and spacing current density distributions have not yet been considered. This paper considers the current density distribution problem of a twin stripe laser, and examines the effect on the distribution of current injection into both stripes, interstripe coupling via the resistance of the p-type cladding layer and the geometric factors of cladding layer thickness, electrode width and spacing. A diode model is assumed for the heterostructure, and finite difference techniques are used to calculate the 2 D potential distribution in the p-type cladding layer and the current density distribution in the active layer. Numerical and experimental results highlight the effect of the nonlinear diode boundary on the current density distribution and show the changes in the current distribution which occur for relatively small fluctuations in current injected into the stripes and equally small changes in the geometry.     

SiGe heterostructure field-effect transistor using V-shaped confining potential well

A working p-type SiGe heterostructure field-effect transistor, utilizing a V-shaped confining potential well as the conducting channel, has been successfully fabricated. The upper boron /spl delta/-doping layer acts as a diffusion barrier to slow diffusion into the undoped Si cap layer. On the other hand, the bottom boron /spl delta/-doping layer prevents hot holes from escaping the channel by improving carrier confinement. It is found that when a V-shaped confining potential well is used as the conducting channel, the devices exhibit the excellent property not only of higher current density but also enhancement in extrinsic transconductance and linear operation range over a wider dynamic range than those of /spl delta/-doped devices for the same dose in SiGe conducting well. The measured transconductance is enhanced three to six times over that of the other /spl delta/ cases.     

Analysis of the cross-coupled lateral mode in a twin-stripefour-contact laser with diagonal current injection

Cross-coupled resonant lateral modes in a twin-stripe four-contact laser are analyzed by coupled-mode theory for conditions in which the current injection into each diagonal pair of stripes is equal. The dependence of the optical power distribution on the laser length and on the carrier-density or the current-density distribution is investigated. The most interesting result is that the highest optical power interesting result is that the highest optical power appears in the waveguide with the lowest carrier density when the carrier-density difference between the adjacent waveguides is small and the laser is shorter than the coupling length. This makes it possible to show that a cross-coupled mode can be supported even in a two-contact twin-stripe laser and that bistable switching between the mode and its mirror image is possible     

Luminescence decay and injected carrier lifetime in the high injection region of AlGaAs lasers

Luminescence decays following short current pulse excitation of an antireflection coated AlGaAs laser diode have been measured. Using an optical gating technique, decays in the high injection region (simgthreshold density of uncoated lasers) were measured with a 100 ps time resolution. The observed luminescence decay is shown to be strongly affected by net gain in the active region. It is also shown that both monomolecular and bimolecular carrier recombination must be considered. A model has been developed that takes these effects into account and is shown to accurately describe steady-state and decay spontaneous emission intensities from laser diodes. A procedure is outlined for determining the necessary device and material parameters for interpreting laser diode characteristics.     

Channeled substrate nonplanar laser analysis--Part II: Lasers with tapered active regions

Light versus current (LversusI) characteristics are calculated for double-heterostructure diode lasers whose active regions decrease in thickness laterally from a maximum on axis. This variation produces lateral real refractive index waveguiding which in turn stabilizes the spatial mode such that the modal field becomes anastigmatic and theLversusIplot becomes linear. In addition to determining threshold current and differential quantum efficiency, we compute the TE00mode patterns, active region charge density distribution, and the power levelP*_{1}at which spatial hole burning causes the TE01mode to begin lasing. The maximum power density at the facet for that power levelP*_{1}is also obtained. All these characteristics are presented as functions of the various device parameters including carrier spontaneous recombination time, diffusion length, optical gain, unpumped band-to-band absorption, internal losses, antiguidance index, wavelength, cladding Al content, active region dimensions, current spreading resistance, facet reflectivity, laser length, and stripe width. Utilizing this information, a design is developed for a laser with low threshold current (40-50 mA) and high differential quantum efficiency (50-65 percent) that operates stable single lowest order (TE00) spatial mode to powers well in excess of 50 mW.