Long-wavelength Si-based MQW photodetectors for application in optical fiber communication

Si-based SiGe/Si strained MQW long-wavelength photodetectors (PD) with cycle type (Ring Shape) waveguide (CWG) and resonant-cavity-enhanced (RCE) structure have been investigated for the first time for improving the quantum efficiency and response time. The results show that the responsivities are higher than that of conventional PD with a same Ge content reported previously. In addition, RCE-PD has an obvious narrow band response with FWHM less than 6nm.

GaInNAs/GaAs quantum well lasers grown by solid-source molecular beam epitaxy

The growth of GaInNAs/GaAs quantum wells (QW) was investigated by solid-source molecular beam epitaxy. N was introduced by a dc-active plasma source. The effect of growth conditions such as on the N incorporation and photoluminescence (PL) intensity of the QWs has been studied. The PL peak intensity decreased and the PL fun width at half maximum increased with increasing N concentrations. The highest N concentration of 2.6% in a GaInNAs/GaAs QW was obtained, and corresponding to a PL peak wavelength of 1.57 mum at 10K. Rapid thermal annealing at 850degreesC significantly improved the crystal quality of the QWs. An optimum annealing time of 5s at 850degreesC was obtained. A GaInNAs/GaAs SQW laser with the emitting wavelength of 1.2 mum and a high characteristic temperature of 115 K was achieved at room temperature.

Wavelength tunable electroabsorption modulated DFB baser with thin film heater

　

A new half-flash architecture for high speed video ADC

In this paper a new half-flash architecture for high speed video ADC is presented. Based on a high speed single-way analog switch circuit, this architecture effectively reduces the number of elements. At the same lime no sacrifice of speed is needed compared with the normal half-flash structure.

Long-wavelength SiGe/Si MQW resonant-cavity-enhanced photodiodes (RCE-PD)

Si1-xGex/Si optoelectronic devices are promising for the monolithic integration with silicon-based microelectronics. SiGe/Si MQW RCE-PD (Resonant-Cavity-Enhanced photodiodes) with different structures were investigated in this work. Design and fabrication of top- and bottom-incident RCE-PD, such as growth of SiGe MQW (Multiple Quantum Wells) on Si and SOI (Si on insulator) wafers, bonding between SiGe epitaxial wafer and SOR (Surface Optical Reflector) consisting Of SiO2/Si DBR (Distributed Bragg Reflector) films on Si, and performances of RCE-PD, were presented. The responsivity of 44mA/W at 1.314 mum and the FWHM of 6nm were obtained at bias of 10V. The highest external quantum efficiency measured in the investigation is 4.2%.

Modification of emission wavelength of self-assembled In(Ga)As/GaAs quantum dots covered by InxGa1-xAs(0 <= x <= 0.3) layer

Red shifts of emission wavelength of self-organized In(Cla)As/GaAs quantum dots (QDs) covered by 3 nm thick InxGa1-xAs layer with three different In mole fractions (x = 0.1, 0.2 and 0.3, respectively) have been observed. Transmission electron microscopy images demonstrate that the stress along growth direction in the InAs dots was reduced due to introducing the InxGa1-xAs (x = 0.1, 0.2 and 0.3) covering layer instead of GaAs layer. Atomic force microscopy pictures show a smoother surface of InAs islands covered by an In0.2Ga0.8As layer. It is explained by the calculations that the redshifts of the photoluminescence (PL) spectra from the QDs covered by the InxGa1-xAs (x greater than or equal to 0.1) layers were mainly due to the reducing of the strain other than the InAs/GaAs intermixing in the InAs QDs. The temperature dependent PL spectra further confirm that the InGaAs covering layer can effectively suppress the temperature sensitivity of PL emissions. 1.3 mum emission wavelength with a very narrow linewidth of 19.2 mcV at room temperature has been obtained successfully from In,In0.5Ga0.5As/GaAs self-assembled QDs covered by a 3-nm In0.2Ga0.2As strain reducing layer. (C) 2001 Elsevier Science B.V. All rights reserved.

Flat Surface Plasmon Polariton Bands in Bragg Grating Waveguide for Slow Light

The formations of the surface plasmonpolariton (SPP) bands in metal/air/metal (MAM) sub-wavelength plasmonic grating waveguide (PGW) are proposed. The band gaps originating from the highly localized resonances inside the grooves can be simply estimated from the round trip phase condition. Due to the overlap of the localized SPPs between the neighboring grooves, a Bloch mode forms in the bandgap and can be engineered to build a very flat dispersion for slow light. A chirped PGW with groove depth varying is also demonstrated to trap light, which is validated by finite-difference time-domain (FDTD) simulations with both continuous and pulse excitations.

Pub/Sub系统中分布式复合事件检测技术研究

随着信息技术的发展，Pub/Sub系统由于具有异步和松耦合的特点，被越来越广泛的应用到金融、供应链管理、物流等领域。在这些应用中，用户对具有各种特定逻辑或时序关系的复合事件的订阅需求越来越迫切，这使得Pub/Sub系统中的分布式复合事件检测技术成为研究的热点，分布式复合事件检测技术包括复合订阅语言、复合匹配算法、以及订阅和事件的路由算法。 目前已有的Pub/Sub系统提供的复合订阅语言比较简单，对时序支持较弱，不能满足实际应用的需要，已有的复合匹配算法也不能有效的支持具有丰富时序关系的复合事件的检测。在路由方面，基于内容的Pub/Sub系统大都是在树结构或者无环图结构的覆盖网络上，采用基于过滤的原子路由方法，该路由方法需要将原子订阅传遍几乎整个网络，以减少订阅匹配的延迟，但这种路由方法很难适应网络的拓扑变化。而目前基于事件空间划分的路由方法不支持事件空间的动态划分和事件空间在不同服务器之间的移动，并且没有提供专门针对事件空间划分的复合事件检测方法。 本文在调研了各种应用需求的基础上，提出了能够表达事件丰富的时序关系、逻辑关系和事件实例关系的复合订阅语言，并且定义了两种事件排序方式。在消费语义采用配对模式的情况下，给出了该语言在两种事件排序方式下的检测结果集的定义。针对该复合订阅语言提出并实现了图结构和时间事件发生器相结合的复合匹配算法，该匹配算法使图结构可以有效的支持时序关系和非触发式事件的检测。在路由方面，首先实现了基于过滤的逆向路径转发的原子路由方法，并在此基础上，实现了就近检测协议，该协议优化了复合订阅匹配结构在网络中的部署。最后，设计和实现了基于事件空间划分的原子路由方法，该路由方法实现了事件空间的动态划分，并可以根据系统中服务器的负载情况实现事件空间的移动，从而有效的平衡服务器的负载。在此基础上，通过对复合订阅的拆分，并利用可移动的复合事件检测器实现了复合订阅的分布式部署和复合事件的分布式检测，同时通过对复合事件检测器的复用，进一步减少了网络负载和服务器的匹配负载。本文还通过实验验证了匹配算法和两种路由方法的性能和开销。

THEORETICAL AND EXPERIMENTAL STUDY OF POLARIZATION CHARACTERISTICS OF POLARIZATION MAINTAINING FIBER BASED ON WAVELENGTH-SWEEPING MODULATION

We analyze theoretically the polarization characteristics of polarization maintaining fiber and study the basic measurement principles of beat length and polarization extinction ratio of this kind of optical fiber. According, to the dependence of the phase difference between two orthogonally polarized modes (denoted Os HE(11)(x) and HE(11)(y)) transmitted in the polarization maintaining fiber on the light wavelength, we propose the wavelength-sweeping modulation method to measure the beat length and the model birefringence. Based on this technique, the hew length and polarization extinction ratio of the PANDA polarization maintaining fibers (PMFs) (provided by Yangtze Optical Fiber and Cable Company, Wuhan, China) were investigated in detail. Experimental results show good consistent with the theoretical ones. We find that this method shows high measurement precision with the advantages of clear measurement principle and easy to operate. 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1466-1469, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25244

Generation of optimized wavelength-tunable optical pulse from an uncooled gain-switched Fabry-Perot semiconductor laser using optical amplifier as external light injection

We present a novel system design that can generate the optimized wavelength-tunable optical pulse streams from an uncooled gain-switched Fabry-Perot semiconductor laser using an optical amplifier as external light source. The timing jitter of gain-switched laser has been reduced from about 3 ps to 600 fs and the pulse width has been optimized by using our system. The stability of the system was also experimentally investigated. Our results show that an uncooled gain-switched FP laser system can feasibly produce the stable optical pulse trains with pulse width of 18 ps at the repetition frequency of 5 GHz during 7 h continuous working. We respectively proved the system feasibility under 1 GHz, 2.5 GHz and 5 GHz operation. (c) 2008 Elsevier B.V. All rights reserved.

Period-doubling bifurcations of the thermocapillary convection in a floating half zone

This study experimentally explored the fine structures of the successive period-doubling bifurcations of the time-dependent thermocapillary convection in a floating half zone of 10 cSt silicone oil with the diameter d (0)=3.00 mm and the aspect ratio A=l/d (0)=0.72 in terrestrial conditions. The onset of time-dependent thermocapillary convection predominated in this experimental configuration and its subsequent evolution were experimentally detected through the local temperature measurements. The experimental results revealed a sequence of period-doubling bifurcations of the time-dependent thermocapillary convection, similar in some way to one of the routes to chaos for buoyant natural convection. The critical frequencies and the corresponding fractal frequencies were extracted through the real-time analysis of the frequency spectra by Fast-Fourier-Transformation (FFT). The projections of the trajectory onto the reconstructed phase-space were also provided. Furthermore, the experimentally predicted Feigenbaum constants were quite close to the theoretical asymptotic value of 4.669 [Feigenbaum M J. Phys Lett A, 1979, 74: 375-378].