Dual-wavelength distributed feedback laser for CWDM based on non-identical quantum well

Using non-identical quantum wells as the active material, a new distributed-feed back laser is fabricated with period varied Bragg grating. The full width at half maximum of 115 nm is observed in the amplified spontaneous emission spectrum of this material, which is flatter and wider than that of the identical quantum wells. Two wavelengths of 1.51 mu m and 1.53 mu m are realized under different work conditions. The side-mode suppression ratios of both wavelengths reach 40 dB. This device can be used as the light source of coarse wavelength division multiplexer communication systems.

Simulation and fabrication of thermo-optic variable optical attenuators based on multimode interference coupler

A type of thermo-optic variable optical attenuator based on multimode interference coupler is proposed. The optical field propagation properties of the devices are simulated using finite difference beam propagation method. The propagation loss of the fabricated device is 2-4.2 dB at the wavelength range 1510-1610 nm. The total power consumption is 370 mW and the maximum attenuation is more than 25 dB, which almost can meet the requirements of optical fiber communication systems.

A VSLMS Style Tap-length Learning Algorithm for Structure Adaptation

Compared with the ordinary adaptive filter, the variable-length adaptive filter is more efficient (including smaller., lower power consumption and higher computational complexity output SNR) because of its tap-length learning algorithm, which is able to dynamically adapt its tap-length to the optimal tap-length that best balances the complexity and the performance of the adaptive filter. Among existing tap-length algorithms, the LMS-style Variable Tap-Length Algorithm (also called Fractional Tap-Length Algorithm or FT Algorithm) proposed by Y.Gong has the best performance because it has the fastest convergence rates and best stability. However, in some cases its performance deteriorates dramatically. To solve this problem, we first analyze the FT algorithm and point out some of its defects. Second, we propose a new FT algorithm called 'VSLMS' (Variable Step-size LMS) Style Tap-Length Learning Algorithm, which not only uses the concept of FT but also introduces a new concept of adaptive convergence slope. With this improvement the new FT algorithm has even faster convergence rates and better stability. Finally, we offer computer simulations to verify this improvement.

A Complex BPF with On Chip Auto-tuning Architecture for Wireless Receivers

A 3(rd) order complex band-pass filter (BPF) with auto-tuning architecture is proposed in this paper. It is implemented in 0.18um standard CMOS technology. The complex filter is centered at 4.092MHz with bandwidth of 2.4MHz. The in-band 3(rd) order harmonic input intercept point (IIP3) is larger than 16.2dBm, with 50 Omega as the source impedance. The input referred noise is about 80uV(rms). The RC tuning is based on Binary Search Algorithm (BSA) with tuning accuracy of 3%. The chip area of the tuning system is 0.28 x 0.22 mm(2), less than 1/8 of that of the main-filter which is 0.92 x 0.59 mm(2). After tuning is completed, the tuning system will be turned off automatically to save power and to avoid interference. The complex filter consumes 2.6mA with a 1.8V power supply.

A 10 Gb/s Directly-Modulated 1.3 mu m InAs/GaAs Quantum-Dot Laser

We demonstrate 10 Gb/s directly-modulated 1.3 mu m InAs quantum-dot (QD) lasers grown on GaAs substrates by molecular beam epitaxy. The active region of the QD lasers consists of five-stacked InAs QD layers. Ridge-waveguide lasers with a ridge width of 4 mu m and a cavity length of 600 mu m are fabricated with standard lithography and wet etching techniques. It is found that the lasers emit at 1293 nm with a very low threshold current of 5 mA at room temperature. Furthermore, clear eye-opening patterns under 10 Gb/s modulation rate at temperatures of up to 50 degrees C are achieved by the QD lasers. The results presented here have important implications for realizing low-cost, low-power-consumption, and high-speed light sources for next-generation communication systems.

移动复制数据库系统冲突检测及消解策略

复制技术是提高移动数据库系统性能的一项关键技术 .该文提出了一种新的移动复制数据库系统模型——事务级结果集传递 (TL RSP)移动复制模型 ,重点分析了该模型中的冲突检测及消解策略 ,并给出了具体的实现算法 ;TL RSP移动复制模型允许移动用户在系统断连时存取数据库的本地副本并提交事务 ,重新连接时进行冲突的检测及消解 ,同时进行事务结果集的合并 ,最后通过增量刷新的方式进行同步处理 ,使得系统最终收敛于一致性的状态 .此外 ,通过引入简化的事务日志、数据版本号以及权限控制等概念 ,TL RSP模型有效地降低了移动数据库系统的资源消耗 ,保证了数据库的一致性 ,从而为移动数据库系统复制提供了一个可行的解决方案

移动数据库系统乐观事务处理策略

在移动数据库系统中 ,计算平台的移动性、频繁的断接性以及长事务等特性使得传统的事务处理模式不再适用 .为了解决移动数据库中的事务处理问题 ,提出了一种新的移动事务处理模型——乐观两阶段提交移动事务模型 ( O2 PC-MT) .该模型采用乐观并发控制与两阶段提交协议相结合的方法 ,对移动事务的长事务特性提供了灵活与有效的支持 ;此外 ,该模型允许移动计算机分多次发送事务操作 ,且在事务执行的过程中可以任意移动 ,从而提供了对交互式事务及随意移动性的支持 .实验结果表明 ,与基于两段锁协议及其变形的其它移动事务处理模型相比 ,O2 PC-MT提高了系统的事务吞吐率并改善了系统的总体性能

复制的移动数据库系统事务级同步处理策略

同步处理技术是保持复制的移动数据库系统一致性的一项关键技术,但现有的事务级同步处理算法存在着一定的局限性.为了克服这些缺陷,并增强其实用性,提出了一种新的移动数据库同步处理模型──基于双时间印的事务级同步(DTSTLS)模型.DTSTLS模型采用了一种三级复制体系结构,系统可以直接使用通用的数据库产品作为其数据库服务器,因此具有良好的可扩充性.作为一种异步的多主副本复制方法,DTSTLS模型允许移动计算机在断连的情况下存取本地副本,从而造成系统短暂的不一致,重新连接时进行冲突检测及同步处理,使系统重新收敛于一致性的状态.此外,通过一种独特的时间印处理策略,DTSTLS模型减少了通信代价,并降低了资源消耗.实验结果表明,DTSTLS模型提高了移动数据库系统的资源利用效率,保证了事务调度的可串行性和数据库的一致性.

An Efficient MMI SOI Splitter with Multimode Input/Output Waveguides

A 1×8 multimode interference power splitter with multimode input/output waveguides in SOI material is designed by the beam propagation method and fabricated by the inductive coupled plasma etching technology for use in fiber optics communication systems.The fabricated device exhibits low loss and good coupling uniformity.The excess loss is lower than 0.8dB,and the uniformity is 0.45dB at the wavelength of 1550nm.Moreover,the polarization dependent loss is lower than 0.7dB at 1550nm.The device size is only 2mm×10mm.

Wide-Band Polarization-Independent Semiconductor Optical Amplifier Gate with Tensile-Strained Quasi-Bulk InGaAs

A semiconductor optical amplifier gate based on tensile-strained quasi-bulk InGaAs is developed. At injection current of 80mA,a 3dB optical bandwidth of more than 85nm is achieved due to dominant band-filling effect.Moreover, the most important is that very low polarization dependence of gain (＜0. 7dB),fiber-to-fiber lossless operation current (70～90mA) and a high extinction ratio (＞50dB) are simultaneously obtained over this wide 3dB optical bandwidth (1520～1609nm) which nearly covers the spectral region of the whole C band (1525～1565nm)and the whole L band (1570～ 1610nm). The gating time is also improved by decreasing carrier lifetime. The wideband polarization-insensitive SOA-gate is promising for use in future dense wavelength division multiplexing (DWDM) communication systems.

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.

Simulation and fabrication of thermo-optic variable optical attenuators based on multimode interference coupler

A type of thermo-optic variable optical attenuator based on multimode interference coupler is proposed. The optical field propagation properties of the devices are simulated using finite difference beam propagation method. The propagation loss of the fabricated device is 2-4.2 dB at the wavelength range 1510-1610 nm. The total power consumption is 370 mW and the maximum attenuation is more than 25 dB, which almost can meet the requirements of optical fiber communication systems.

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IEEE

移动机器人人机互助行走监控方法研究及其实际应用

由于行走监控在移动机器人技术中的独特地位和作用，使得其问题解决路线与最终性能极大地影响着构成系统的实用性及用户接受程度．本文通过剖析行走监控同其他模块的内在联系，深入地讨论了研究此问题的必要性和困难所在．最后，结合一个实际应用系统，给出了行之有效的指导思想、实现策略和关键问题解决途径。