FREQUENCY RESPONSE OF FIBER RING RESONATOR AND ITS APPLICATION IN DFB LASER WAVELENGTH VARIATION MEASUREMENT

Frequency response of a fiber ring resonator (FRR) composed of an ordinary optical coupler and a segment of optical fiber is theoretically and experimentally investigated. The frequency response equation based oil small-signal modulation is derived and studied in detail. It is shown that the shape of the frequency response curve is very sensitive to the wavelength; as a result, the FRR can be applied to measure the wavelength of a lightwave source with high resolution. With this method, we demonstrate the measurement of tiny changes of wavelength of a DFB laser. (C) 2009 Wiley Periodicals. Inc. Microwave Opt Technol Lett 51 2444-2448, 2009 Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24608

Dynamic P-I and P-V Curves for Semiconductor Lasers and Modulators

In this paper, we propose the dynamic P-V curve for modulator and P-I curve for laser diode, and present a simple approach to deriving the curves from the small-signal frequency responses measured using a microwave network analyzer. The linear response range, modulation efficiency, optimal driving conditions at different frequency can, therefore, be determined. It is demonstrated that the large-signal performance of electro-absorption (EA) modulator and the directly modulated semiconductor lasers can be predicted from the dynamic curved surface. Experiments show a good agreement between the evaluated characteristics and the measured large-signal performance.

Temperature Sensitivity Dependence on Cavity Length in p-Type Doped and Undoped 1.3-mu m InAs-GaAs Quantum-Dot Lasers

We have fabricated 1.3-mu m InAs-GaAs quantum-dot (QD) lasers with and without p-type modulation doping and their characteristics have been investigated. We find that introducing p-type doping in active regions can improve the temperature stability of 1.3-mu m InAs-GaAs QD lasers, but it does not, increase the saturation modal gain of the QD lasers. The saturation modal gain obtained from the two types of lasers is identical (17.5 cm(-1)). Moreover, the characteristic temperature increases as cavity length increases for the two types of lasers, and it improves more significantly for the lasers with p-type doping due to their higher gain.

Decoherence of two Josephson charge qubits coupled via sigma(x)sigma(x)-type coupling and exposed to sigma(x) noise

Decoherence properties of two Josephson charge qubits coupled via the sigma(x)sigma(x) type are investigated. Considering the special structure of this new design, the dissipative effects arising from the circuit impedance providing the fluxes for the qubits' superconducting quantum interference device loops coupled to the sigma(x) qubit variables are considered. The results show that the overall decoherence effects are significantly strong in this qubit design. It is found that the dissipative effects are stronger in the case of coupling to two uncorrelated baths than are found in the case of one common bath.

Study of optical properties in GaAs1-xSbx/GaAs single quantum wells

GaAsSb/GaAs single quantum wells (SQWs) grown by molecular beam epitaxy are studied by selectively-excited photoluminescence (SEPL) measurement. For the first time, we have simultaneously observed the PL, from both type I and type II transitions in GaAsSb/GaAs heterostructure in the SEPL. The two transitions exhibit different PL, behaviours under different excitation energy. As expected, the peak energy of type I emission remains constant in the whole excitation energy range we used, while type U transition shows a significant blue shift with increasing excitation energy. The observed blue shift is well explained in terms of electron-hole charge separation model at the interface. Time-resolved(TR) PL exhibits more type 11 characteristic of GaAsSb/GaAs QW. Moreover, the results of the excitation-power-dependent PL and TRPL provide more direct information on the type-II nature of the band alignment in GaAsSb/GaAs quantum-well structures. By combining the experimental results with some simple calculations, we have obtained the strained and unstrained valence band offsets of Q(v) = 1.145 and Q(v)(0) = 0. 76 in our samples, respectively.

Selectively excited photoluminescence of GaAs1-xSbx/GaAs single quantum wells

GaAsSb/GaAs single quantum wells grown by molecular-beam epitaxy are studied by selectively excited photoluminescence measurements. We have simultaneously observed the photoluminescence (PL) from both type-I and type-II transitions in the samples. The two transitions exhibit different PL behavior under different excitation energies. As expected, the peak energy of the type-I emission remains constant in the entire excitation energy range we used, while the type-II transition shows a significant blueshift with increasing excitation energy. The observed blueshift can be well explained by an electron-hole charge separation model at interface. This result, along with the excitation-power-dependent PL and the measured longer carrier decay time, provides more direct information on the type-II nature of the band alignment in GaAsSb/GaAs quantum well structures. (C) 2002 American Institute of Physics.

A novel ultra-narrow transmission-band fiber Bragg grating and its application in a single-longitudinal-mode fiber laser with improved efficiency

A novel design approach to ultra-narrow transmission-band fiber Bragg grating (FBG) is proposed and demonstrated for the first time. The new grating consists of multiple identical distributed-Bragg reflector (DBR) cavities and a it-phase-shifted gap, and hence, the proposed laser is constructed by the cascade of these identical DBR fiber lasers. By manufacturing the proposed grating in a piece of Er-Yb codoped fiber, a single-wavelength single-longitudinal-mode (SLM) fiber laser with improved efficiency is demonstrated experimentally. The experimental results show that the pump-to-signal conversion efficiency of the proposed laser is improved by a factor of two in comparison with the optimized distributed-feedback (DFB) fiber lasers. (c) 2007 Elsevier B.V. All rights reserved.

A dual-wavelength sampled fiber Bragg grating and its application in L-band dual-wavelength erbium-doped fiber lasers

A novel dual-wavelength (DW) sampled fiber Bragg grating (SFBG) is proposed and demonstrated for the first time to the author's best knowledge. This kind of SFBG can realize a DW operation with uniform reflection peaks rather than multiple nonuniform peaks shown in conventional SFBGs. Based on the designed SFBG, we have proposed a novel L-band DW erbium-doped fiber laser, which has such a unique merit that the spacing of the two wavelengths keeps unchanged during tuning laser.

Solid-core tellurite glass fiber for infrared and nonlinear applications

By optimizing glass composition and using a multistage dehydration process, a ternary 80TeO(2)-10ZnO-10Na(2)O glass is obtained that shows excellent transparency in the wavelength range from 0.38 mu m up to 6.10 mu m. Based on this optimized composition, we report on the fabrication of a single-mode solid-core tellurite glass fiber with large mode area of 103 mu m(2) and low loss of 0.24 similar to 0.7 dB/m at 1550 nm. By using the continuous-wave self-phase modulation method, the non-resonant nonlinear refractive index n(2) and the effective nonlinear parameter gamma of this made tellurite glass fiber were estimated to be 3.8x10(-1)9 m(2)/W and 10.6 W-1.m(-1) at 1550 nm, respectively. (C) 2009 Optical Society of America

I 蓖麻油聚氨酯/聚甲基丙烯酸甲酯AB交联聚合物的研究 II 双阳原油热处理中加入降凝剂的研究

用蓖麻油与TDI反应生成端异氰酸酯基预聚物，再与HEA反应，生成端乙烯基预聚物，以不同比例的MMA与端乙烯基预聚物共聚交联，得到一组组成和交联密度各不相同的ABCP样品；为了分别观察组成和交联密度对材料性能的影响，在交联共聚过程中，以二乙烯基苯作交联点调节剂 ，得到固定组成，交联密度变化和固定交联密度组成变化的两组样品；此外，在固化过程中加入不同含量的丙烯酸（<10%），得到另一组样品，以观察氢键对该体系的影响。反应过程中用化学分析、NMR、IR及平衡溶胀等方法测定反应程度、分子量及交联网的交联密度；同时用动态粘弹谱仪和介电损耗仪测定样品的动态力学性能，转变与松弛及相容性；用材料试验机测试样品的力学性能；通过透射电子显微镜观察材料的形态结构。结果表明：copu/PMMA ABCP是个半相容体系，随硬段含量的增加和交联密度的减小相容性变差。形态结构呈不规则形状，相区尺寸由几A变至几百A，材料的力学性能和阻尼性能明显优子构成它们的均聚物。材料的阻尼值主要受交联密度的影响，玻璃化转变温度则主要受组成控制。氢键对该体系的形态结构有明显影响，丙烯酸含量为7.5%时相容性最差，5%和10%时最好。以双阳昌10号井原油为研究对象选用EVA作原料，以马来酸酐接枝改性，合成ET-6降凝剂。采取在热处理中加入降凝剂的综合处理方法，考察了降凝剂合成的最佳反应条件和降凝剂用量及热处理温度对原油结晶状态及流动性的影响。结果表明，热处理中加入ET-6降凝剂可使蜡的结晶形态发生明显变化，降凝剂用量仅100-500 ppm即可使双阳原油的凝固点由原来的30-31 ℃降至7-9 ℃，原油的低温流动性大为改观。

共生固氮放线菌Frankia的细胞化学分类I、Frankia菌全细胞可溶性蛋白图谱分析II、Frankia菌同功酶图谱分析

本文利用单向SDS-PAGE方法对十八株Frankia菌的全细胞可溶性蛋白进行了图谱分析。Frankia菌蛋白图谱不受菌令的影响。不同交叉接种组的Frankia菌具有不同的蛋白图谱，同一交叉接种组内的菌株也有所羞。十八株菌分为三大类七个亚类，第I类包括赤场、杨梅香蕨木和美洲茶内生菌；第II类包括木麻黄内生菌，第III类包括胡颓子和沙棘内生菌。利用同功酶图谱的差异性对Frankia菌进行分类识别是一种非常有效的方法，不同的Frankia菌株具有不同的同功酶（过氧化物酶和酯酶）图谱。根据图谱之间的相似性，可以将二十株Frankia菌分成三组；即赤杨组，木麻黄组和胡颓子组，这与其它分类结果基本符合，只是细枝木麻黄菌株CcO1的过氧化物酶图谱与其它菌株完全不同。从同种根瘤中分离的内生菌具有不同的同功酶图谱，进一步证实了遗传结构不完全相同的菌株可以同时共生于同种根瘤内，同时根据二种同功酶的电泳分布率，说明了Frankia菌株遗传信息的广泛分布性。

Ab initio study on the physical properties of CoN3 and RhN3 with skutterudite structure

The elastic and electronic properties of hypothetical CoN3 and RhN3 with cubic skutterudite structure were studied by first principles calculations based on density functional theory. By choosing different initial geometries, two local minima or modifications were located on the potential energy surface, termed as modifications I and II. Both compounds are mechanically stable. For each compound, modification I is lower in energy than II. Thermodynamically stable phases can be achieved by applying pressures. Modification II is lower in energy than I at above 50 GPa for both compounds.