Optical properties of an InGaAs-InP interdiffused quantum well

A comprehensive model is developed for the calculation of polarization-dependent absorption coefficients and refractive index of the InGaAs-InP interdiffused multiple-quantum-well at room temperature for wavelengths ranging from 1.1 to 2.4 μm. Groups III and V types of interdiffusion are considered separately. The as-grown structure is a latticed-matched In_0.53Ga_0.47As-InP structure with a well width of 60 Å. The optical transitions consist of a full quantum-well calculation together with Γ,X, and L valleys contributions and through the Kramers-Kronig transformation to link the real and imaginary parts of the dielectric functions. The results show that group-III-only interdiffusion produces compressive strain and results in a band-edge red shift and refractive index enlargement, while the tensile strain induced by group-V-only interdiffusion results in a vice verse effect. This provides a left and right tunable band edge and positive and negative index steps dependent on the interdiffusion process. A small and constant birefringence of 0.005 at around 1.55 μm can also be obtained over a 50-nm wavelength range by using group-V-only interdiffusion. These properties have strong implications in realizing a tunable and high-performance device as well as for photonic integrations     

Optical devices from AlGaAs-GaAs HBTs heavily doped with amphotericSi

A new optoelectronic multifunctional device, having triple function of light emission, detection and amplification have been developed and some preliminary integrated circuits are demonstrated. The devices consist of N-p-n or N-P-n AlGaAs-GaAs HBT utilizing amphoteric Si heavily-doped GaAs or AlGaAs p-type base layer. Maximum current gain of 3600, and light output power of about 0.17 μW with 100 μA base current (I_b) in transistor mode operation and of about 10 μW with I_b=40 mA in diode mode operation are obtained. The optical emission wavelengths in both are about 0.85-0.86 μm. Optical gain of about 130 was obtained near the 0.86 μm wavelength as a detection transistor. Spectrum matching between emission and detection wavelength range is achieved. Some monolithic integrated circuits constituted of the transistors are proposed and demonstrated successfully. The relationship between current gain and radiative quantum efficiency at the transistor operation is also discussed     

Optical gain and gain suppression of quantum-well lasers withvalence band mixing

The effects of valence band mixing on the nonlinear gains of quantum-well lasers are studied theoretically for the first time. The analysis is based on the multiband effective-mass theory and the density matrix formalism with intraband relaxation taken into account. The gain and the gain-suppression coefficient of a quantum-well laser are calculated from the complex optical susceptibility obtained by the density matrix formulation with the theoretical dipole moments obtained from the multiband effective-mass theory. The calculated gain spectrum shows that there are differences (both in peak amplitude and spectral shape) between this model with valence band mixing and the conventional parabolic band model. The shape of the gain spectrum calculated by the new model becomes more symmetric due to intraband relaxation together with nonparabolic energy dispersions. Optical intensity in the GaAs active region is estimated by solving rate equations for the stationary states with nonlinear gain suppression     

随机分布介质中的光学特性

无序增益介质作为一种新的研究对象,它有一些特殊的效应,如后向相干散射、漫射激光、干涉效应等。文章对这些效应作一个初步的探讨和粗略的描述。     

Modal analysis of IncGaAsP-InP,GaAs/AlGaAs-GaAs,and InGaAsP/AlGaAs-GaAs MIS heterostructure lasers

The transverse modal behavior of Metal-Insulator (Oxide)-Semiconductor (MIS) heterostructure injection lasers is analyzed. MIS structures have been proposed by Jain and Marciniec as an alternate approach to p-n heterojunctions to obtain minority carrier injection and subsequent lasing action. In the modal analysis the MIS structure is treated as an asymmetrical three-layer slab waveguide with appropriate boundary conditions. Numerical computations of electric field strength, intensity and confinement factor P are presented for various GaAs and InP based MIS structures. A comparison of the output characteristics of a GaAs MIS laser with a conventional GaAs p-n double heterostructure laser is also reported.     

Eigenstates and absorption spectra of interdiffused AlGaAs-GaAsmultiple-quantum-well structures

We present a comprehensive analysis of the inter-well coupled eigenstates in interdiffused AlGaAs-GaAs multiple quantum-well structures. A full numerical calculation is considered without any approximation or presumption of the eigenstates. During the initial interdiffusion in the quantum-well structure with well and barrier thickness equaling 100 Å, the wavefunctions behave as in the case of a single quantum well with almost no well-to-well coupling of the states. However, as interdiffusion proceeds, the eigenstate in each subband forms minibands, as in the case of superlattice. Distortion of the coupled wavefunctions can also be observed as a consequence of the nonuniformity of the confined wells at the far sides of the multiquantum-well core. The polarized absorption coefficients, including valence band-mixing, are also calculated. Results show that the blue shift of the absorption edge is greater in the range of 10 Å⩽L _d⩽30 Å. The two-dimensional quantum-well properties are at its strongest in the beginning of interdiffusion. An estimation of the modulator performance also shows an improvement of the contrast ratio and lower absorption loss during the initial stage of interdiffusion. This predicts wavelength tuning range of almost 60 nm     

Optical gain and luminescence of a ZnO-MgZnO quantum well

The optical gain and the luminescence of a ZnO quantum well with MgZnO barriers is studied theoretically. We calculated the non-Markovian optical gain and the luminescence for the strained-layer wurtzite quantum well taking into account the excitonic effects. It is predicted that both optical gain and luminescence are enhanced for the ZnO quantum well when compared with those of the InGaN-AlGaN quantum well structure due to the significant reduction of the piezoelectric effects in the ZnO-MgZnO systems.     

Optical gain and large-signal characteristics of illuminated GaAs MESFET's

The illuminated large-signal characteristics of a uniformly doped epitaxial GaAs MESFET have been measured when optically gated with an He-Ne laser source. The dependence of the measured optical gains on the applied electrical biases and optical intensity, position, and spot size indicate that the dominant dc gain mechanisms are transit time photoconductivity combined with an effective photovoltaic change in the pinchoff voltage. The photovoltaic change in the pinchoff voltage dominates for high optical power levels, while the photoconductive response dominates for low power levels. Optical gains in the range of 5-10 were measured for the photoconductive regime, while gains in the range of 50-70 were measured for the photovoltaic regime.     

A model of the interdiffused multilayer process

The interdiffused multilayer process (IMP) is a novel approach to growing Hg_1−xCd_xTe. In this process, alternating thin films of HgTe and CdTe are grown and allowed to interdiffuse resulting in a bulk material of constant composition. A model of the IMP must include the effects of both the deposition of new material and the interdiffusion of the material. It must also be able handle the flush phases of the IMP where the growth rate decays to zero. Existing approaches to modeling epitaxial growth of Hg_1−xCd_xTe treat growth and interdiffusion as separate, sequential steps resulting in numerical stability problems, pseudodiffusion effects, or flush phase modeling problems. The model presented here, however, is based on an incremental balance where growth and diffusion occur simultaneously, resulting in a model exhibiting none of the difficulties mentioned above. The IMP growth model is integrated with a model for calculating reflectance from a laser directed at near normal incidence angle. The predicted reflectance is compared to experimental measurements and showed a good preliminary fit when the model employed default parameters. The agreement is greatly improved after parameter fitting.     

Optical gain in a strained-layer quantum-well laser

The optical gain and the refractive index change of a uniaxially stressed GaAs-Al₂Ga_1-xAs quantum-well laser is studied theoretically using the multiband effective mass theory (k -p method) and density matrix formalism with intraband relaxations. It is found that uniaxial strain of the quantum well substantially alters the subband structures and the optical gain of the quantum-well laser. In particular, the gain of the TM mode increases while the gain of the TE mode decreases with increasing stress. Thus, the threshold current either decreases or increases with the stress, depending on whether the laser is operating in a TM or TE mode     

光折变二波耦合增益振荡

1 引言 光折变二波耦合增益振荡在光学长度—频率转换仪、实时波前反转、激光腔中的畸变修正、光计算及相关存储器等中有广泛的应用。就其振荡器的类型可分为自泵浦相位共轭振     

Optical gain of strained wurtzite GaN quantum-well lasers

A theory for the electronic band structure and the free-carrier optical gain of wurtzite-strained quantum-well lasers is presented. We take into account the strain-induced band-edge shifts and the realistic band structures of the GaN wurtzite crystals. The effective-mass Hamiltonian, the basis functions, the valence band structures, the interband momentum matrix elements, and the optical gain are presented with analytical expressions and numerical results for GaN-AlGaN strained quantum-well lasers. This theoretical model provides a foundation for investigating the electronic and optical properties of wurtzite-strained quantum-well lasers.     

增益金纳米球壳光学特性研究

通过有限元方法研究了增益系数以及核壳比对纳米核壳结构表面等离激元共振特性的影响，并且对球心为增益介质、球壳为金的纳米核壳结构进行了数值模拟。计算结果表明：随着增益系数增大到临界值，散射截面增大近2x105倍，吸收截面变为负值，消光截面近似为0，电场强度增强近185倍，谐振带宽从60nm缩小到1nm。同时，随着核壳比的增大，吸收及消光共振峰均发生红移现象。我们的相关结果可为增益介质在金属纳米结构中的应用提供了理论参考和技术支持。     

Optical gain and saturation characteristics of quantum-dot semiconductor optical amplifiers

Detailed theoretical analysis of the gain characteristics of quantum-dot semiconductor optical amplifiers (QD-SOA) is presented. An analytical expression for the optical gain is derived from the quantum dot and wetting layer rate equations. Due to the better confinement of carriers in the quantum dots, our calculation shows that large unsaturated optical gain can be obtained at low operating current. Also, we found that the output saturation intensity of QD-SOA is higher than the output saturation intensity of bulk-SOA. This fact lends itself to the design of efficient low-power SOAs.     

Optical mode properties of laterally offset gain and index guidingstructures

We describe the mode properties of offset gain and index guided structures in which gain and index guiding effects are simultaneously present and oriented in parallel but laterally offset. Such structures can occur in semiconductor lasers, integrated optics, and optical waveguides. Within the parabolic approximation the resulting waveguide modes are found to be Hermite-Gaussian functions with complex-valued Gaussian mode parameters and centerlines. The lateral positions and far-field angles of these modes can be controlled by modifying the gain and index guiding parameters, permitting both transverse mode displacement and output beam steering     

Modeling of excitonic electrorefraction in InGaAsP multiple quantumwells

The absorption spectra in an InGaAsP/InP multiple quantum well for different values of electric field, applied perpendicularly to the quantum well layer planes, are delineated by modifying the model given by P.J. Stevens et al. (IEEE J. Quantum Electron., vol.24, pp.2007-2015, 1988). The essential deviations in the present model lie in the inclusion of the additional broadening of excitons due to composition fluctuation in the quaternary, the forbidden transition between the second heavy hole subband and the first conduction subband, an improved excitonic envelope function dependent on both the in-plane and transverse separation of electrons and holes, and a modified calculation of oscillator strength. The modeled curve's are then used to calculate the values of Δn, the change in refractive index due to field, and the ratio Δn/Δk, where Δk is the extinction coefficient, using Kramers-Kronig relations. The calculated values are found to agree with the experimental data for 1.537 μm     

Optical gain spectra of InGaAsP/InP double heterostructures

We report the first optical gain measurements on InGaAsP/ InP double heterostructures with composition corresponding to an emission wavelength of about 1.3 μm at 300 K. At optical pumping levels of about 1 MW/cm²the maximum gain values of the best samples available are 800 cm^-1at 2 K, 500 cm^-1at 77 K, and 200 cm^-1at 300 K. We conclude from low-intensity luminescence and absorption spectra, that the laser transition corresponds to free-carrier recombination between band-tail states, which are present even in not intentionally doped material. Although these tail states result in rather broad low-intensity luminescence, narrow gain spectra comparable to those of GaAs/GaAlAs double heterostructures are obtained.     

Large Stark shift of the interband transition in two-step quantumwells

Large and near-linear Stark shifts of the electron-heavy-hole ground state excitonic transition were observed in photoluminescence (PL) measurements for a two-step quantum-well (TSQW) structure. The Stark shift was 40 meV while a corresponding square well shifted only 20 meV at a field of 70 kV/cm. The observed Stark shifts agreed well with calculations. The large Stark shift of the TSQW was achieved on a global-to-local state transition realized via tailor-made quantum well (QW) parameters. This structure is an ideal candidate for optoelectronic devices based on the quantum confined Stark effect (QCSE)     

Optical gain in GaAs/GaAlAs graded-index separate-confinementsingle-quantum-well heterostructures

Optical model gain in both the TE and TM polarizations of graded-index separate-confinement single-quantum-well heterostructure lasers measured at various levels of injection current on samples with different quantum-well widths is discussed. Lasers with wide quantum wells (⩾120 Å) have emission and gain spectra which exhibit two peaks, caused by the n=1 and n=2 subband transitions. With ordinary cavity parameters, the saturation gain of the n=1 subband transitions is lower than the cavity loss of the laser, and the lasers always lase at the n=2 transitions. Reducing the quantum-well width increases the saturation gain of the n=1 transitions enough to allow lasing from them, even in cases of higher cavity loss. Further, for a fixed cavity loss, reduction of the quantum-well width decreases the threshold current density for n =1 lasing transitions, while that for n=2 lasing increases. The superlinear increase of the material gain with the decrease of the well width reduces the minimum cavity length for n =1 subband lasing. Narrower quantum wells with higher mirror reflectivity allow shorter cavity lengths while retaining n=1 lasing, resulting in low threshold current