Below-band-gap waveguiding behaviors of a weakly index-guided GaAs/AlGaAs quantum well laser

We report the reduced waveguiding efficiency for the signals around 1560 nm as the injection current of an GaAs/AlGaAs multiple quantum well laser diode (lasing wavelength at 840 nm) with a ridge-loading waveguide configuration increased. This reduction trend stopped when the injection current reached the threshold condition of the laser diode. The decreased waveguide transmission and the more expanded mode profile indicated the variation of the effective refractive index gradient in the lateral dimension with injection current. This variation was due to the refractive index decrease with increasing carrier density even below band gap. A slab waveguide model was used to simulate the lateral mode profile variation with injection current. The refractive index differences between the guiding layer and claddings in the slab waveguide model provided estimates of refractive index contrasts of the laser diode at a concerned wavelength under various injection conditions.     

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.     

含左手材料异质结构光子晶体的零平均折射率带隙的展宽

运用光学传输矩阵理论,研究了含左手材料一维二元光子晶体的禁带特性.提出了含左手材料的光子晶体异质结构中零平均折射率带隙展宽的方法.根据此方法设计的异质结构的光子晶体形成的零平均折射率带隙,与一维光子晶体零平均折射率带隙相比,零平均折射率带隙的宽度和相对带隙宽度可以得到显著的拓宽.而且它的零平均折射率带隙的边缘与TM波和TE波相关.这种特性在微型谐振腔、天线基片、同轴波导等方面都具有潜在的应用.     

Theory of the double heterostructure laser: II. Waveguide model incorporating carrier concentration-dependent refractive index

Solutions to charge transport equations are used to illustrate the variation of the active region refractive index of the double-heterostructure GaAs laser. It is shown that a marked asymmetry can arise in the refractive index. In this paper, a suitable waveguide theory is developed to take account of this effect. The necessity for such a waveguide theory is demonstrated by comparing threshold current densities and far-field patterns calculated with this model to those calculated using a simpler waveguide model.     

条形半导体激光器光束质量因子M2的理论计算

通过一个二维半矢量模型求得纯折射率导引脊形波导和掩埋波导这两种常见平面条形半导体激光器波导结构的模式光场分布，现通过描述光束传播的非傍轴矢量二阶矩，通过平面波谱的方法获得激光器出射光束在横向和侧向上的束腰、远场发散角和M^2因子。讨论了波导结构参量变化对M^2因子的影响，并对两种波导结构光束的性质与波导参量的关系进行了比较。     

Bistable operation of a GaAs-AlGaAs diode laser coupled to an external resonator of narrow spectral bandwidth

The influence of an external dispersive resonator on the emission properties of a double heterostructure semiconductor laser operating at room temperature has been investigated. The proper design of the external resonator (frequency selectivity and efficient back-coupling of the radiation leaving the diode) demonstrates that a laser with optical feedback can show bistability and hysteresis phenomena. The dispersive bistability has its origin in the dependence of the refractive index on carrier density, temperature and optical power. Hysteresis curves have been measured by changing the injection current or by tuning the dispersive element. We have found a threshold in the injection current for the onset of the hysteretic behaviour. Moreover, a theoretical model has been established to explain the essential features of the experimental results. Hysteresis cycles for different experiments have been calculated.     

Temperature-dependent optical properties of GaSe layered single crystals

Optical properties of GaSe single crystals have been investigated using temperature-dependent transmission and room temperature reflection measurements in the wavelength range of 380–1100 nm. The analysis of the absorption data at room temperature showed the existence of indirect transitions in the crystal with energy band gap of 1.98 eV. Temperature dependence of the transmission measurements revealed the shift of the absorption edge toward lower energy as temperature is increased from 10 to 280 K. The rate of change of the indirect band gap was found as γ = ?6.6 × 10^?4 eV/K from the analysis of experimental data under the light of theoretical relation giving the band gap energy as a function of temperature. The absolute zero value of the band gap energy and Debye temperature were calculated from the same analysis. The Wemple–DiDomenico single-effective-oscillator model applied to refractive index dispersion data was used to determine the oscillator energy, dispersion energy, oscillator strength and zero-frequency refractive index values.     

Theoretical analyses on improved beam properties of GaSb-based 2.X-μm quantum-well diode lasers with no degradation in laser parameters

An asymmetric laser heterostructure is developed to improve the beam properties of GaSb-based diode lasers with no degradation in laser parameters.Employing the semivectorial finite difference method,the dependences of beam divergence and optical confinement factor on waveguide width and refractive index step are investigated theoretically.After carefully design,a particular asymmetric laser structure is proposed.Its beam divergence in the fast axis is reduced from 61° to 34° compared with that of the broad-waveguide structure.The optical confinement factor is approximately equal to 0.0362 and comparable to that of the conventional broad-waveguide structure.     

Influence of inhomogeneous distribution of the minority carriers on the doping dependence of the threshold current in EBP lasers using n-type GaAs at 300°K

The influence of inhomogeneous distribution of the minority carriers on the doping dependence of the threshold current in electron-beam-pumped (EBP) lasers using n-type GaAs at 300°K is studied theoretically. It is found that when inhomogeneity exists, the threshold current is weakly dependent on the doping concentration in agreement with the experimental observation.     

梳状波导结构中石墨烯表面等离子体的传播性质

理论上研究了介质/石墨烯/介质梳状波导结构中表面等离子体的传播性质. 波导中表面等离子体模的有效折射率随着石墨烯费米能级的提高而减小, 随着介质折射率的增加而增加. 分析和仿真结果表明, 基于这种梳状波导可以在中红外波段实现新型的纳米等离子体滤波器, 器件的尺度在几百纳米的范围. 通过改变梳状分支的长度, 石墨烯的费米能级, 介质的折射率和波导中石墨烯的层数, 很容易来调节带隙的位置. 另外, 滤波带隙的宽度随着梳状分支数的增加而增加. 这种滤波性质将在可调的高集成光子滤波器件中具有潜在的应用.     

p型GaAs的远红外波段光学特性

砷化镓(GaAs)是太赫兹波段半导体异质结构激光器的重要材料之一,为了获得p型GaAs材料在远红外波段的光学特性,采用气态源分子束外延(GSMBE)技术在半绝缘GaAs(100)衬底上生长了掺Be的p型GaAs薄膜材料,其载流子浓度从1.54×1015~1.85×1019cm-3。用远红外变换傅里叶光谱仪测量了其远红外反射光谱,并对反射光谱进行了理论模拟和分析,计算得出了不同空穴浓度的p型GaAs在远红外波段的折射率、消光系数和吸收系数。发现在这一波段消光系数和吸收系数均随着载流子浓度的增加而增大,吸收系数最大值可达到4.0×104cm-1。     

Design and optimisation of high-brightness 980 nm laser diodes with distributed phase correction

Designs for 980 nm Al _x Ga_1–x As/In_0.2Ga_0.8As/GaAs high-power, high-brightness semiconductor lasers/amplifiers with distributed phase correction and short-cavity lengths (i.e. cavity lengths 560–1040 m) are presented. The proposed lasers/amplifiers employ a single mode feed waveguide coupled to a power amplifier with a laterally graded effective refractive index (GRIN) profile to control the lateral mode shape and phase. The lateral index of the power amplifier has a hyperbolic secant (HYSEC) profile, which can be approximately realised by tailoring the effective refractive index of the amplifier using a series of discrete etches. The epitaxial and structure designs of the laterally discretised GRIN lasers/amplifiers are presented. Finally, a method for improving the effective refractive index discretisation is described.     

锥形太赫兹量子级联激光器输出功率与光束特性研究

针对锥形太赫兹量子级联激光器, 利用有限差分波束传播法和速率方程法, 建立了准三维的太赫兹有源器件仿真模型, 能够对具有轴向非线性波导结构的激光器进行模拟. 利用此模型, 研究了锥角大小对激光器输出光功率及光束质量的影响. 仿真结果表明, 考虑到器件之间的光耦合效率, 为了达到最大的有效输出光功率, 锥形太赫兹量子级联激光器的锥角存在一个最优值.     

Vis-NIR characteristics of amorphous germanium films and electrical properties of a-Ge/<Emphasis Type="Italic">p</Emphasis>-Si heterostructures obtained by pulsed-laser deposition method

Optical properties of a-Ge films (glass substrate) and electrical properties of a-Ge/p-Si heterostructures obtained by the pulsed-laser deposition method have been studied. It is shown that optical properties of a-Ge films can be well explained by the Tauc model for amorphous semiconductors. The dependence of optical gap on the film thickness is obtained for a-Ge films. Forward-bias current-voltage characteristics of the a-Ge/p-Si heterostructures are satisfactorily approximated by the relation for current density J = CV ^m , where m varies from 1.45 to 1.95 depending on the applied forward bias and a-Ge film thickness. Also, for the mentioned heterostructure (a-Ge film thickness is 400 nm) nearly quadratic dependence of the current density is observed, which indicates the predominance of the space-charge-limited current.     

Refractive indices and related properties of some potential mixed crystals

The high frequency refractive indices of some binary, ternary and quaternary mixed crystals have been evaluated from the knowledge of plasmon energy and the lowest gap energy of the crystals for their applications in heterojunctionled and solar cells. The Fermi energy screening factor correction has been applied to effect accuracy in prediction. The model has been used to study the temperature and pressure dependence of refractive index. The calculated value agrees with experiment (within a few percent) justifying the validity of the model.     

Modulation behavior of semiconductor injection lasers

GaAs double heterostructure semiconductor injection lasers which now exhibit more than 25000 h cw room temperature lifetime are of great interest for future use as directly modulated transmitters for high bit-rate fiber optical communications. The effects limiting this application are modulation distortions, spectral width and additional spectral broadening in the case of modulation and spontaneous fluctuations of the output power. The dynamic and spectral behavior of injection lasers, the methods of high bit-rate modulation and the improvement of the high bit-rate modulation capability by coupling two lasers are discussed.     

Leaky Modes in Ag Nanowire over Substrate Configuration

By launching surface plasmons propagating along the Ag nanowire deposited on a substrate, we clearly observe three leaky modes using the Fourier imaging method. The effective refractive indexes, propagation lengths and electric field distributions of the modes are investigated, which indicate that the energy of the mode with a lowest effective refractive index is mainly distributed in the air, while for the other two modes, it is mainly distributed in the substrate and in the gap between the Ag nanowire and the substrate. These modes enable such a configuration to be used as a multichannel waveguide or highly directional optical antenna, which is of fundamental importance for optical device miniaturizations and photonic circuit integrations.     

非对称波导结构提高980nm激光二极管电光效率的机理研究

采用高电流注入条件下的载流子扩散方程和复折射率波导模型情况下的亥姆霍兹方程,对980nm高功率激光二极管外延材料的非对称和对称波导结构的光吸收损耗进行了理论计算。采用低压金属有机化学气相外延技术制备了两种波导结构的外延材料,并制作了激光器件,进行了光电特性测试和对比分析。理论计算和实验结果表明:与对称波导结构相比,非对称波导结构外延材料并未减小光吸收损耗,而是减小了串联电阻,因而降低了器件的焦耳热损耗,从而提高器件的电光效率。     

Optimization of a non-cryogenic quantum infrared detector

A study of the optimization of the detectivity of a mid-infrared double heterostructure photovoltaic detector is proposed. Simple approximate analytic expressions for the dark current are compared with full numerical calculations, and provide a physical insight into the mechanisms dominating the dark current. The analysis is performed step by step, from a simple p–n junction to the full double heterostructure. The influence of temperature, barrier band gap energy in a double heterostructure, doping density in the active region, on diffusion and generation–recombination mechanisms is analyzed. It is finally shown how the performances of a double heterostructure photovoltaic detector can be improved by controlled doping of the active region.     

Optical properties of amorphous HF–In–Zn–O thin films estimated from transmission spectra

Amorphous and flat (<1 nm roughness) Hf–In–Zn–O thin films were prepared by radio frequency (rf) magnetron sputtering method at room temperature (RT) and at 300 °C substrate temperature. The crystal structure and surface morphology were investigated by high resolution X-ray diffraction (HR-XRD) and atomic force microscopy (AFM), respectively. Optical properties of these films were obtained from the UV–VIS–NIR transmission spectra, at normal incidence, over the 200–2000 nm spectral range. Swanepoel's method was used to calculate the thickness and the refractive index of the films. The dispersion of refractive index was obtained in terms of the single-oscillator Wemple–DiDomenico model. The optical absorption edge was described using the direct transition model proposed by Tauc. The film deposited at higher substrate temperature had lower optical band gap, higher refractive index, higher oscillator strength and energy of the effective dispersion oscillator. Optical characterization shows that films become more stable, relaxed and rigid at higher substrate temperature.