布里渊光时域分析传感器的消偏振衰落技术

在布里渊光时域分析(BOTDA)光纤传感器中,由于受激布里渊散射的偏振相关性的影响,激励光和探测光的偏振态随机变化引起的信号起伏严重影响布里渊散射光信号的稳定测量。通过建立与偏振态有关的激励光和探测光的耦合方程,推导出接收探测光光强关于激励光和探测光偏振态的理论公式,并由此提出偏振扩展接收技术。理论分析表明,偏振扩展接收技术可以有效地抑制偏振相关信号衰落。通过对耦合方程进行模拟,验证了理论分析的正确性和偏振扩展接收技术的可行性。最后给出了采用偏振扩展接收的布里渊光时域分析实验结果,与理论分析和模拟具有较好的一致性。     

增益钳制半导体光放大器的静态特性分析

采用增益钳制半导体光放大器的时域模型,用MATLAB计算其静态特性,着重分析了放大器的输入信号光与增益的相关性.结果表明,在注入电流一定的情况下,输入信号光与放大器的增益呈相反方向变化,但是增益带宽积不变.     

掺铒玻璃波导放大器中抽运光信号光重叠因子分析

通过分析掺铒(Er3 )玻璃波导放大器(EDWA)的放大增益机理,提出抽运光与信号光光模场分布之间的归一化重叠积分因子(Γ),并引入到掺铒波导放大器增益模拟计算中,使理论模型更切合实际。以Ag -Na 二次离子交换工艺制作的具有埋入型渐变折射率分布的掺铒波导放大器为例,采用数值方法模拟了条形波导截面上的二维折射率分布及抽运光、信号光的光模场分布。计算了不同工艺参量设置下的Γ大小,讨论Γ对放大器增益的影响。结果显示,在二次离子交换制作过程中设置适当工艺参量优化折射率分布,能有效改善波导中抽运光与信号光光模场分布之间的重叠因子,提高掺铒波导放大器的增益。计算结果显示,在一定条件下,Γ从0.5增至0.8,每厘米长度掺铒波导放大器的放大增益可提高近1.5 dB。     

电子束潘宁阱非中性等离子体中电子聚心约束实验

介绍了电子束潘宁阱非中性等离子体实验。利用具有小正则角动量电子束的注入,在装置中形成了有稠密核心的电子等离子体。当潘宁阱中电磁场匹配是,约束电子的散射最强。注入电子束的束流强度超过一定的阈值时,电子聚心状态才能形成。阈值与潘宁阱电场成正比。     

离轴高功率双程放大系统中小信号增益系数 与泵浦能 密度关系研究

描述了在多程放大装置上首先实现了高功率、大口径、方光束的双程离轴放大。对由 8片N31 玻璃片组成的放大器的增益特性做了测试。在充电电压为 2 2 k V、泵浦能密度为 1 0 .2 4 J/ cm3时 ,小信号增益系数为 4 .0 8% cm- 1 。     

Instability of Stimulated Brillouin Scattering in a Fiber Ring Resonator

We investigate theoretically the instability of transient stimulated Brillouin scattering (SBS) in a high- finesse fiber ring resonator consisting of a fiber ring and directional coupler. Unlike many reports to date, the linear phase detuning of the cavity is taken into account. It is found that SBS instabilities including the self-pulsing and chaotic behavior can occur even if the length of the fiber resonator is very short. SBS instabilities depend strongly on the linear phase detuning, the input power, and the coupling coefficient of the coupler.     

Elastic anomalies and orientational glass transition in Na(CN) Cl mixed crystals. A Brillouin spectroscopic study

High performance Brillouin spectroscopy (BS) has been used to study the elastic properties (static and dynamic) of the orientational glassy state of Na(CN)_xCl_1-x samples ). The temperature behaviour of the elastic properties reveals a more complex scenario for the orientational glass transition than generally believed. The shear elastic constant shows the well-known c ₄₄ ( T ) anomaly, indicated by a minimum, found in other cyanide mixed crystals. The results obtained for the hypersonic attenuation are in clear contradiction with the dynamic character of the c ₄₄ ( T )-minimum. The temperature behaviour of the longitudinal elastic constant c₁₁ of very dilute Na(CN)_xCl_1-x samples shows two striking features: i) Similar to the anomalous temperature behaviour of c ₄₄ ( T ), lowering the temperature c ₁₁ ( T ) first decreases, goes through a minimum and then rises again. The minimum takes place at a temperature above the temperature, , where c ₄₄ ( T ) reaches its minimum value. ii) A kink-like anomaly of c ₁₁ ( T ) is observed at lower temperatures. This second anomaly is similar to the classical one observed in canonical glasses at their glass transition temperature . Received 8 April 1999 and Received in final form 3 June 1999     

Self-Aligned SiGe MOS-Gate FET with Modulation-Doped Quantum Wire Channel for Millimeter Wave Application

This paper describes a self-aligned SiGe MOS-gate field-effect transistor (FET) having a modulation-doped (MOD) quantum wire channel. An analytical model based on modified charge control equations accounting for the quantum wire channel, is presented predicting the transport characteristics of the MOS-gate MODFET structure. In particular, transport characteristics of devices having strained SiGe layers, realized on Si or Ge substrates, are computed. The transconductance g_m and unity-current gain cutoff frequency (f_T) are also computed as a function of the gate voltage V_G. The calculated values of f_T suggest the operation of one-dimensional SiGe MODFETs to be around 200 GHz range at 77°K, and 120 GHz at 300°K.     

利用相位共轭镜产生高质量宽度可调脉冲

实验研究了双池受激布里渊散射系统中的脉冲压缩。通过简单地改变双池间距可以获得脉宽可调的优质光束,脉宽可调范围依赖于抽运能量。增大抽运能量,脉宽可调范围也相应地增大。对双池受激布里渊散射系统的脉冲波形进行了数值模拟,理论计算结果与实验符合得很好。     

准Λ型四能级原子系统在弱场中的增益及电磁感应透明

利用数值模拟的方法讨论了稳态下准型四能级原子与两光场相互作用系统对探测场的增益以及与粒子数布居规律之间的关系。结果表明即使在场较弱的情况下,随着探测场和它所对应能级间跃迁频率失谐量的变化,系统在所有拉比频率相位为零时对探测光总会同时呈现三个增益峰和两个固定的产生电磁感应透明(EIT)现象的位置,并且当系统呈现电磁感应透明的同时,探测场所对应的高能级粒子数为零;而拉比频率相位的变化则会导致系统对探测光既有吸收也有增益,并且也呈现电磁感应透明现象,但仅仅相位的变化并不影响高能级的粒子数分布。值得注意的是该结果均在精确求解下所得。