共查询到19条相似文献,搜索用时 78 毫秒
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激光通信技术是实现高效通信的重要手段.大气激光通信链路中,大气的散射、吸收和湍流严重制约激光传输质量.分析了激光通信系统中由于大气湍流和色散造成的脉宽展宽,计算了脉宽展宽量与湍流大气折射率结构常数、初始脉宽和传输距离之间的关系;比较了不同发射激光脉宽、不同发射能量下的脉冲波形特性.数值计算及仿真结果表明,激光脉宽随传输距离、大气湍流的增大而增大,长脉宽的超短脉冲激光受大气湍流和色散的影响小,并且脉宽增大,激光功率降低,研究结论对超短脉冲的应用具有一定的意义. 相似文献
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针对常用Henyey-Greenstein散射相函数(H-G散射相函数)在描述单个粒子前向及后向散射特性时的不准确性,提出将基于 T 矩阵法的散射相函数用于激光烟尘散射研究的方法。通过 T 矩阵法计算烟尘粒子单次散射特性,并提出基于离散散射相函数的散射角抽样方法,利用随机数描述多重散射的散射分布,结合光子的半解析接收方法,建立了激光引信在烟尘环境下发射及接收的理论模型。为验证理论模型的正确性,通过封闭烟尘环境实验室,对激光引信在实际烟尘环境下的接收能力进行测试,分析不同烟尘浓度及湿度条件对回波的影响,并与采用H-G散射相函数理论模型的计算结果进行对比。结果表明,随着烟尘浓度和湿度的增加,激光回波幅度也相应增大,且基于 T 矩阵散射相函数的回波仿真方法与实验结果更吻合,尤其是烟尘浓度较大的情况,实验与理论分析结果一致。 相似文献
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从理论上分析了影响激光脉冲宽度的因素,建立了脉冲展宽与各影响因素之间的数学模型。通过 Matlab 软件模拟分析了不同因素对脉冲展宽的影响,分析得出在一定条件下,脉冲展宽效果最佳时分束镜反射率 R =0.38,光学腔长 L =940 cm。对 Nd ∶YAG 脉冲激光器纳秒激光进行了脉冲展宽实验,测试了脉冲宽度随着泵浦电压的变化情况。选取了泵浦电压为730 V,分束镜 R 为0.38,在初始脉宽为37 ns 的条件下通过改变腔长将激光脉冲分别展宽到37.5 ns,42 ns 和55 ns,实验数据与理论分析的误差分别0.98%,0.74%和2.1%。实验数据分析验证了建立的数学模型是可行的。 相似文献
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利用猫眼效应原理实施目标主动探测,能够快速、准确发现空间光学侦察设备。激光脉冲辐照不同的反射目标,产生回波经大气传输后具有不同的脉冲展宽,利用该特性可实现对不同目标的识别和定位。利用光子散射理论分析了近地面气溶胶散射效应引起的脉冲展宽,给出了影响脉冲展宽的主要因素,建立了猫眼和漫反射背景回波脉冲展宽的计算物理模型;为验证模型,设计并实施了基于飞艇平台的动态主动探测验证实验,实验结果表明:激光脉冲经过8~10 km斜程大气传输,猫眼和飞艇背景漫反射回波分别展宽了20~30 ns和90 ns,与物理模型计算值具有较好的一致性,验证了物理模型的正确性,该模型可为区分和提取猫眼回波信号提供理论依据。 相似文献
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介绍了一种利用脉冲展宽特性识别云和地面目标的方法—蒙特卡罗方法,来排除大气中云对目标的干扰。利用包含返回概率模型的半解析蒙特卡罗方法模拟返回信号的展宽特性,大大提高了计算效率。在对δs函数入射波脉冲展宽分析的基础上,对脉宽分别为1ns、100ns、1μs的矩形入射波的脉冲展宽进行了模拟分析。结果显示:当入射波脉宽为1ns和100ns时,云层对波形的展宽明显大于地面目标的展宽,易于区分;当入射波脉宽为1μs时,云层和地面目标的展宽作用相当,不易区分;对于更加稠密的积雨云与层云,脉冲展宽相对于积云变窄。这些为实际应用中入射波脉宽以及探测器参数的选择提供了指导作用。 相似文献
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This paper describes a new computer-aided design tool especially conceived for the efficient time-domain simulation of highly heterogeneous nonlinear wireless communication circuits, i.e., combining RF and baseband analog circuitry and digital components. Using multirate Runge-Kutta algorithms within a multi time framework, to benefit from the different rates of variation of slowly varying (latent) and fast-varying (active) currents and voltages (state variables), we managed to solve the envelope transient regime of circuits excited by AM and PM RF carriers, in a highly efficient way. Indeed, with the adoption of convenient sampling rates for the multiple time representations of the slowly varying and fast-varying state variables, gains of more than one order of magnitude in simulation time are reported, even for an illustrative circuit example of very small size. 相似文献
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Developing full-wave simulators for high-frequency circuit simulation is a topic many researchers have investigated. Generally speaking, methods invoking analytic pre-processing of the device's V-I relations (admittance or impedance) are computationally more efficient than methods employing a numerical procedure to iteratively process the device at each time step. For circuits providing complex functionality, two-port or possibly multiport devices whether passive or active, are sure to appear in the circuits. Therefore, extensions to currently available full-wave methods for handling one-port devices to process multiport devices would be useful for hybrid microwave circuit designs. In this paper, an efficient scheme for processing arbitrary multiport devices in the FDTD method is proposed. The device's admittance is analytically pre-processed and fitted into one grid cell. With an improved time-stepping expression, the computation efficiency is further increased. Multiport devices in the circuit can be systematically incorporated and analyzed in a full-wave manner. The accuracy of the proposed method is verified by comparison with results from the equivalent current-source method and is numerically stable 相似文献
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光纤技术为惯性约束聚变激光驱动器前端系统提供了许多便利,如便于分路、鲁棒性和稳定性.提出了一套全光纤前端的方案来适应未来高能拍瓦激光装置对种子源的需求.实验研究了这套用于产生高能短脉冲激光的光纤前端系统的啁啾脉冲展宽与放大特性.采用锁模振荡器的相位锁定信号作为系统的参考时钟,将各级光开关器件进行同步.系统采用波导幅度调制器来选取需要的信号重复频率,并用声光调制器(AOM)对放大器级间放大自发辐射(ASE)光进行抑制.通过大模场光纤放大器后系统输出啁啾脉冲峰值功率4.1 kW,脉宽760 ps,输出脉冲稳定.鲁棒性、高可靠性和使用便捷的优点使这套前端系统为高能拍瓦激光装置提供了一种可选择的种子脉冲产生方式. 相似文献
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A. A. Al-Jabr M. A. Alsunaidi 《Journal of Infrared, Millimeter and Terahertz Waves》2009,30(11):1226-1233
In this paper a new general numerical algorithm for the simulation of heterogeneous dispersive structures is presented. The
general algorithm is based on the ADE-FDTD approach. It finds its strength in the simulation of cases where different materials
with different dispersion types are present. Several numerical examples are presented and results are compared to analytical
solutions. While having the same level of accuracy, the proposed algorithm offers savings in both memory and computational
requirements, compared to other ADE-based methods. 相似文献
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ZHANG Zaifeng XU Guangzhu MA Yide 《电子学报:英文版》2008,(2):293-296
In this paper, an efficient method for iris feature extraction using the Pulse coupled neural network (PCNN) is proposed. In order to segment out those iris features such as crypts, furrows, spots in the iris image, the PCNN network is introduced. And the output pulse image produced by PCNN is chosen as the iris codes. At last the performance of the proposed approach is demonstrated with experiments. Encouraging results demonstrated that the proposed iris features extraction method is able to produce a representation that allows for discriminating a large number of iris patterns. 相似文献
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目标的短脉冲散射问题本质上是其宽带散射特性,从时域上获取短脉冲散射问题更为直接。时域物理光学方法具有计算速度快、物理近似意义清晰明确等特点,可直接计算电大尺寸目标的微波短脉冲散射的时域波形。介绍了时域物理光学的理论公式,通过三角型网格剖分建立目标模型,引入Radon 变换计算目标的“冲击响应”,利用卷积计算获得目标的微波短脉冲散射时域波形。通过仿真算例进行验证,计算双导体球模型散射回波验证了该方法的可行性;计算大飞机的微波短脉冲散射波形展示了该方法处理电大尺寸问题的能力。用该方法计算的目标短脉冲散射回波波形可直接作为信号处理研究的输入。 相似文献