Tunable MQW-DBR lasers using selective area growth

The tunable ridge waveguide distributed Bragg reflector (DBR) lasers designed for wavelength-division-multiplex (WDM) communication systems at 1.55 um by using selective area growth (SAG) is reported. The threshold current of the DBR laser is 62mA and the output power is more than 8mW. The isolation resistance between the active region and the Bragg region is 30K Ohm. The total tuning range is 6.5nm and this DBR laser can provide 6 continuous standard WDM channels with 100GHz channel spacing; in the tuning range, the single mode suppression ratio (SMSR) is maintained more than 32dB and the maximum output power variation is less than 3dB.

Single ridge waveguide electroabsorption modulated DFB laser for 2.5Gb/s transmission

In this paper we proposed a single ridge waveguide electroabsorption modulated distributed feedback laser (EML) for long-haul high-speed optical fiber communication system. This EML was successfully fabricated by two step metal organic vapor phase epitaxy (MOVPE) including selective area growth (SAG) and helium partially implantation. No obvious changes of the threshold current (< 0.2 mA), extinction ratio (< 0.1 dB), output power (< 0.2 dBm) and isolation resistance were achieved in the preliminary aging test. With 2.5 Gb/s NRZ modulation, no power penalty was observed after the optical signal was transmitted through 280 Km normal single mode fiber.

Strained MQW electro-absorption modulators with high extinction ratio and low capacitance

We fabricate an electro-absorption modulator for optical network system using a new strategy, the improved modulation properties of the strained InGaAs/InAlAs MQW show it's polarization independent, high extinction ratio (> 40dB) and low capacitance (C <0.6pF) which can achieve an ultra-high frequency(> 10GHz). The device is be used in 10Gbps optical time division multiplex (OTDM) system as a signal generator.

Wavelength tunable electroabsorption modulated DFB baser with thin film heater

　

Growth of Fe doped semi-insulating InP by LP-MOCVD

The semi-insulating InP has been grown using ferrocene as a dopant source by low pressure MOCVD. Fe doped semiinsulating InP material whose resistivity is equal to 2.0x10(8)Omega*cm and the breakdown field is Beater than 4.0x10(4)Vcm(-1) has been achieved. It is found that the magnitude of resistivity increases with growing pressure enhancement under keeping TMIn, PH3, ferrocene (Fe(C5H5)(2)) flow constant at 620 degrees C growth temperature. Moreover, the experimental results which resistivity varies with ferrocene mole fraction are given. It is estimated that active Fe doping efficiency; eta, is equal to 8.7x10(-4) at 20mbar growth pressure and 620 degrees C growth temperature by the comparison of calculated and experimental results.

1.3 mu m InGaAsP/InP strained layer multi-quantum-well complex-coupled distributed feedback laser

1.3 mu m strained-layer multi-quantum wells complex-coupled distributed feedback lasers with a wide temperature range of 20 to 100 degrees C are reported. The low threshold current of 10mA and high single-facet slope efficiency of 0.3mW/mA were obtained for an as cleaved device. The single mode yield was as high as 80%.

Proof of InAs/GaAs self-organized quantum dot lasing and the experimental determination of local Strain effect on the band structures

Confirmation of quantum dot lasing have been given by photoluminescence and electro-luminescence spectra. Energy levels of QD laser are distinctively resolved due to band filling effect, and the lasing energy of quantum dot laser is much lower than quantum well laser. The energy barrier at InAs/GaAs interface due to the built-in strain in self-organized system has been determined experimentally by deep level transient spectroscopy (DLTS). Such barrier has been predicted by previous theories and can be explained by the apexes appeared in the interface between InAs and GaAs caused by strain.

Static and dynamic electric field domain formation in a doped GaAs/AlAs superlattice

We have observed the transition from static to dynamic electric field domain formation induced by a transverse magnetic field and the sample temperature in a doped GaAs/AlAs superlattice. The observations can be very well explained by a general analysis of instabilities and oscillations of the sequential tunnelling current in superlattices based solely on the magnitude of the negative differential resistance region in the tunnelling characteristic of a single barrier. Both increasing magnetic field and sample temperature change the negative differential resistance and cause the transition between static and dynamic electric field domain formation. (C) 2000 Elsevier Science B.V. All rights reserved.

Electronic characteristics of InAs self-assembled quantum dots

Deep-level transient spectroscopy and photoluminescence studies have been carried out on structures containing self-assembled InAs quantum dots formed in GaAs matrices. The use of n- and p-type GaAs matrices allows us to study separately electron and hole levels in the quantum dots by the deep-level transient spectroscopy technique. From analysis of deep-level transient spectroscopy measurements it follows that the quantum dots have electron levels 130 meV below the bottom of the GaAs conduction band and heavy-hole levels at 90 meV above the top of the GaAs valence band. Combining with the photoluminescence results, the band structures of InAs and GaAs have been determined. (C) 2000 Elsevier Science B.V. All rights reserved.

Design of Photonic Crystal Semiconductor Optical Amplifier With Polarization Independence

Slow-light effects in photonic crystal (PC) waveguides can enhance light-mater interaction near the photonic band edge, which can be used to design a short cavity length semiconductor optical amplifier (SOA). In this paper, a novel SOA based on slow-light effects in PC waveguides (PCSOA) is presented. To realize the amplification of the optical signal with polarization independence, a PCSOA is designed with a compensated structure. The cascaded structure leads to a balanced amplification to the TE and TM polarized light.

Formation trends of ordered self-assembled nanoislands on stepped substrates

The growth of ordered self-assembled nanoislands on stepped substrates is studied systematically by kinetic Monte Carlo simulations. As the terrace width is small, the formation of nanoislands is confined in the steps and nanoislands ordered in lines or nanowires can be obtained. The Schwoebel barrier at the step edges has a great influence on the evolution of both the size and space distributions of the islands. When the terrace width is relatively large, self-ordering of nanoislands in the center regions of the terraces happens. An unexpected trend of the nanoisland self-ordering is found as the deposition thickness is larger than 0.2 ML, which can be related to the attractive migrations between nearby islands.

High Characteristic Temperature InGaAsP/InP Tunnel Injection Multiple-Quantum-Well Lasers

We fabricate 1.5 mu m InGaAsP/InP tunnel injection multiple-quantum-well (TI-MQW) Fabry-Perot (F-P) ridge lasers. The laser heterostructures, including an inner cladding layer and an InP tunnel barrier layer, are grown by metal-organic chemical-vapor deposition (MOCVD). Characteristic temperature.. 0 of 160K at 20 degrees C is obtained for 500-mu m-long lasers. T-0 is measured as high as 88K in the temperature range of 15-75 degrees C. Cavity length dependence of T-0 is investigated.

Sequential coupling transport for the dark current of quantum dots-in-well infrared photodetectors

The dark current characteristics and temperature dependence for quantum dot infrared photodetectors have been investigated by comparing the dark current activation energies between two samples with identical structure of the dots-in-well in nanoscale but different microscale n-i-n environments. A sequential coupling transport mechanism for the dark current between the nanoscale and the microscale processes is proposed. The dark current is determined by the additive mode of two activation energies: E-a,E-micro from the built-in potential in the microscale and E-a,E-nano related to the thermally assisted tunneling in nanoscale. The activation energies E-a,E-micro and E-a,E-nano decrease exponentially and linearly with increasing applied electric field, respectively.

金黄色葡萄球菌肠毒素C2的结构特征与生物学功能研究

通过PCR技术对Staphylococcal enterotoxin C2(SEC2)的氨基端和羧基端部位进行删除突变。研究结果显示删除羧基端77个氨基酸对SEC2超抗原和致热活性没有显著影响，但更进一步的删除导致SEC2活性显著降低。而少量氨基端残基删除则可导致SEC2超抗原活性显著降低，说明SEC2超抗原活性主要集中于其氨基端部位。以上研究结果也表明SEC2分子的完整性并不是其超抗原活性所必需的。 对二硫环及Zn结合位点配位组氨酸残基在SEC2分子中的生物学功能进行研究。以定点突变技术构建SEC2二硫环突变蛋白，从而干扰二硫键的形成。研究结果表明干扰二硫环形成对SEC2的超抗原、催吐和致热等活性均有显著影响，说明二硫环在维持SEC2生物学活性方面具有重要作用。此外，针对Zn结合位点配位组氨酸残基的研究结果显示突变118位和122位组氨酸后对SEC2的超抗原活性没有有显著影响，而47位组氨酸的突变导致SEC2分子的超抗原活性显著降低。动物实验结果显示分别突变118位和122位组氨酸残基后均导致SEC2分子催吐及热源活性显著降低，而47位组氨酸突变仍具有较高的催吐和致热活性。说明Zn结合位点配位组氨酸残基在SEC2的催吐、致热和超抗原活性中扮演了重要的作用，并进一步揭示肠毒素诱导的超抗原和致热活性之间没有明显的相关性。 以Leu及Glu分别替代20和22位氨基酸残基后SEC2超抗原活性有显著提高，并将具有减毒作用的组氨酸位点突变引入上述活性增强的SEC2突变，从而构建减毒突变蛋白。结果显示引入118和122位组氨酸双突变后突变蛋白保留了与SEC2相当的超抗原和抗肿瘤活性，但与SEC2相比致热活性有显著下降，为减毒SEC2超抗原药物的开发提供了可能性。 为探索金黄色葡萄球菌的体内基因突变方法，本研究对金黄色葡萄球菌基因组中的α-溶血毒素基因进行敲除。首先构建同源重组质粒pMHL-α，经金黄色葡萄球菌RN4220修饰后再通过原生质体转入金黄色葡萄球菌SM-01。含重组质粒pMHL-α的金黄色葡萄球菌SM-01在42℃诱导条件下培养多代，最终筛选出α-溶血毒素基因缺失菌株。经序列分析和血平板溶血实验结果证实最终获得产SEB金黄色葡萄球菌α-HL缺失菌株。为构建产减毒肠毒素的金黄色葡萄球菌基因工程菌株提供了一定的理论基础和方法。

OLAND生物脱氮系统运行条件及其微生物群落结构的研究

OLAND两阶段生物脱氮系统是一项正在开发且极具应用前景的处理高氨氮、低COD废水的新技术。在实验室水平，对OLAND系统限氧亚硝化阶段MBR反应器和厌氧氨氧化阶段SBR反应器的启动和运行进行了系统研究。MBR反应器控制参数在DO0.1-0.3mg/L，pH7.8±0.1，温度30±0.5℃，SRT无穷大的条件下，可实现在较高的容积负荷By＝IO00mgN／L，水力停留时间HRT：ld下稳定的亚硝酸型硝化，使NH4+-N和NO2-N的出水比例达到理想的比值（1:1.20±0.20），保证厌氧氨氧化阶段SBR反应器的理想进水；SBR反应器在完全厌氧、pH7.8-8.2，温度30±0．5℃，SRT无穷大的条件下，无需外加任何有机碳源，在较高总氮负荷550mgN／L下，可实现NH4+-N和NO2--N同时稳定的去除，二者的消耗比例为1:（1.21±0.05），总氮去除率高达92％。采用巢式PCR、DGGE、 FISH等分子技术对MBR反应器硝化菌群随溶解氧的动态变化规律和SBR反应器厌氧氨氧化菌群结构、组成进行了研究，并探讨了硝化菌群与氮素组成变化之间的内在联系。结果表明：在限氧亚硝化阶段硝化菌群中氨氧化菌受溶解氧浓度的影响较大，其种群结构从反应器启动初期到稳定后期发生了非常明显的变化。亚硝酸氧化菌NOB的种群组成受溶氧影响并不明显，从启动初期到稳定后期其种群结构无明显变化。硝化菌群中氨氧化菌 AOB与亚硝酸氧化菌NOB的数量比例关系随溶解氧的降低而不断升高，从最初的3.6:1升高到稳定后期的5.5:1。MBR反应器优势硝化菌群主要由A、B、C三类氨氧化菌和硝化杆菌D、硝化螺菌F组成，其中优势菌C为维持MBR反应器稳定出水比例的主要功能菌。硝化菌群组成和结构的变化，带来了不同N素之间组成和比例的规律性变化。厌氧氨氧化阶段基本由厌氧氨氧化菌AnAOB和ANAMMOX两类菌组成，二者空间结构紧密，在反应器中的活菌数量比例分别为55％和42％。厌氧氨氧化菌AnAOB种群多样性相对比较丰富，主要由条带I和H所代表的两种优势菌组成；ANAMMOX菌种群多样性变化较小，其种群主要由优势菌K和J组成。对MBR和SBR反应器中的优势菌进行了克隆、测序和系统发育学分析，结果表明：限氧亚硝化阶段MBR反应器启动初期的优势菌A属于Nitrosomonadaceae科，是否是一个新属，还有待于进一步鉴定。运行中期优势菌B与Nitroso）nonaseurooaea亲缘关系最近，同源性高达99.1％，暂命名为Nilrosomonas sp.BI。稳定后期优势菌C与Nitrosomonas eutroPha亲缘关系最近，同源性为96.3％，暂命名为Nifrosomonas sp．cl。硝化杆菌属优势菌D与Nitrobacter alkalicus、Nitrobacter hambllrgensts和Nitlobac招rwinograsky 亲缘关系较近，同源性分别为95.5-97％、96.5～97％和95.8～96.8％。SBR反应器中AnAOB优势菌I与MBR反应器优势菌B亲缘关系最近，同源性高达98.7％，与Nitlosomonas euroPaea同源性为98.3％。根据序列比较和生理特性分析，优势菌I与优势菌B应为Nitrosomonas属两个不同的种，暂将优势菌I命名为Nitrosomonas sp．II。优势菌H与MBR反应器优势菌C亲缘关系最近，同源性达97.9％，与Nitrosomonas eutropha同源性为96.3％。结合其生理特性分析，二者应为Nitrosomonas属两个不同的种，暂将优势菌H命名为Nitrosomollas sp．Hl。ANAMMox优势菌K与未培养的 Planctomycete和已鉴定的另一种ANAMMoX菌尤uenenia sf况ttgartiensis亲缘关系较近，同源性分别为99.8％和96.6％。优势菌J与Gen bank收录的所有菌的相似性均低于76％，说明该菌是OLAND系统厌氧氨氧化阶段比较独特的菌，是迄今为止在厌氧反应过程中未发现的一个新菌。