Generation of DQPSK format and its performance against polarization mode dispersion

We propose a novel transmitter and receiver for differential quadrature phase-shift keying （DQPSK） format. The impact of the first-order polarization mode dispersion （PMD） on systems using DQPSK with 100- Gb/s non-return-to-zero （NRZ） or return-to-zero （RZ） format is investigated. Through computing the eye openings of DQPSK formats under different PMD conditions, it is found that NRZ DQPSK, as compared with RZ DQPSK, incurs smaller eye opening due to PMD. Carrier-suppressed return-to-zero （CSRZ） DQPSK format has better tolerance than RZ DQPSK format to PMD for a given bit rate.     

Efficient continuous-wave eye-safe region signal output from intra-cavity singly resonant optical parametric oscillator

We report an efficient continuous-wave (CW) tunable intra-cavity singly resonant optical parametric oscillator based on the multi-period periodically poled lithium niobate and using a laser diode (LD) end-pumped CW 1064 nm Nd:YVO₄ laser as the pump source. A highly efficiency CW operation is realized through a careful cavity design for mode matching and thermal stability. The signal tuning range is 1401-1500 nm obtained by varying the domain period. The maximum output power of 2.2 W at 1500 nm is obtained with a 17.1 W 808 nm LD power and the corresponding conversion efficiency is 12.9%.     

适用于非常规工作环境中热释电型激光能量计的研制

现有的激光能量计传感器灵敏度系数都与其所处环境温度有关,在-50℃～70℃的温度范围内,灵敏度偏差较大,直接影响测量结果。为了达到消除环境温度的影响,采取在不同环境温度下对热释型能量计的灵敏度进行校准的研究方法。该校准方法与普通激光能量计的校准方法的不同之处在于对热释电型能量计进行校准时,温度由室温扩展到-50℃～70℃的温度范围。利用环境试验箱,每隔10℃固定一个温度点,进行激光能量的测量实验,得到各个温度点所对应的灵敏度修正系数,再借助最小二乘法建立起各个温度点上能量计灵敏度系数同环境温度的函数关系,从而实现了-50℃～70℃的温度范围内激光能量的准确计量。研制能直接工作于非常规工作环境下的热释电型激光能量计,对解决激光能量测量的外场需求有一定现实意义。     

Bipolar resistance effect observed in CdSe quantum-dots dominated structure of Zn/CdSe/Si

In this study, we report our new finding of bipolar resistance effect (BRE) in quantum dots (QDs)-embedded structure of Zn/CdSe/Si. This effect features a remarkable linear resistance change and an enhanced BRE when a laser moves along the surface of the structure. The results show that the combination of BRE with QDs is useful for applications and may add a new functionality to QDs-based optoelectronic devices.     

微重力下低温贮箱压力控制技术进展

针对微重力下低温贮箱压力升高的问题,简要介绍了几种常用的低温贮箱压力控制的方法及原理,讨论了它们各自存在的问题,并简要展望未来低温贮箱压力控制技术的发展方向。文章指出,未来研究重点在于将主动制冷与被动绝热相结合,实现零蒸发贮存的热转移技术。     

板条增益介质波前畸变诊断方法

对波前重构算法中的区域法进行了改进,使其能够应用于板条增益介质的波前畸变诊断。利用该方法对47块Nd: YAG板条增益介质沿厚度方向波前畸变进行测量,指出镀膜和加工等环节对增益介质的波前畸变可能造成的影响。按照波前畸变峰谷（PV）值对测量结果进行了统计,结果表明:增益介质造成的静态波前畸变参差不齐,测量样本中静态畸变PV值最多可达5 m以上,且仅有4.1%的增益介质静态畸变PV值小于1 m。通过选取某些增益介质使之级联,测量其组合波前畸变,发现在系统中使用两块波面互补的增益介质有助于减小系统的静态波前畸变。     

含指数项广义平方映射的分岔和吸引子

由平方映射延伸构造出了一类含指数项的广义平方映射,并由一维映射通过一次耦合项得到了二维映射.利用一参数分岔图、二参数动力学行为分布图、映射迭代曲线和吸引子相图等方法对这类广义平方映射进行了分析和仿真.研究结果表明：一维广义平方映射分布在一个单位区域内的,有着与单峰平方映射相类似的非线性动力学现象;而二维广义平方映射则存在Hopf分岔和锁频等现象,有着复杂多变、形状奇异的极限环和混沌吸引子. 关键词： 广义平方映射 分岔 迭代曲线 吸引子     

热声热机声场的格子气分析

从格子气自动机演化方程恢复了宏观热声方程,采用D2Q9热格子气模型模拟热声热机系统的压力场、温度场和速度场,获得压力驻波的传播和反射过程。模拟结果显示,在所给模拟条件下压力波具有非线性的特征,变截面附近的流场区域会产生引起非线性耗散的涡流。本文也分析了谐振管几何尺寸及格子气粒子密度对系统频率和压力的影响,验证了热声热机格子气模型的有效性。     

On creation of Hopf bifurcations in discrete-time nonlinear systems

Bifurcation characteristics of a nonlinear system can be manipulated by small controls. In this paper, we present a control method to create Hopf bifurcations in discrete-time nonlinear systems. The critical conditions for the Hopf bifurcations are discussed. The center manifold method, normal form technique and the Iooss's Hopf bifurcation theory are employed in the derivation of the control gain. Numerical demonstration is provided. (c) 2002 American Institute of Physics.     

反旋双色圆偏振激光场下Ar原子非次序双电离研究

应用经典系综方法模拟了反旋双色圆偏振激光场下Ar原子非次序双电离过程.双电离概率随激光强度变化曲线呈现出"knee"结构,表明了明显的电子关联特征.通过调节倍频与基频激光场的场强比可以实现对双电离的增强或抑制以及最优化.在"knee"结构区域的不同场强下,这种调控机制具有相似性.通过分析重碰撞和激发电离的时间特征,进一步讨论了反旋双色圆偏振激光场的强度对不同电离通道的控制规律.