不同放电管边界条件对氦镉激光噪声的影响

本文研究不同毛细管边界条件对氦镉激光噪音(尤其是对电离波频率调制度)的影响,并对行走辉纹沿管轴的分布作了探讨。     

圆柱固 液结构声子晶体的全反射隧穿效应

为了研究一维固-液结构圆柱形声子晶体中弹性波的全反射隧穿效应,利用转移矩阵法计算了弹性波在大于全反射角入射一维圆柱形声子晶体的透射率。在透射波中发现了全反射隧穿效应,得出了全反射隧穿峰的频率随模式量子数的变化特征,全反射隧穿峰的频率随圆柱半径的的变化特征,全反射隧穿峰的峰数随周期数的变化特征。并利用波的量子理论和倏逝波的理论对一维声子晶体的隧穿效应作出了定性的理论解释。     

相对论电离波前导致的频率上移

介绍了电磁波与相对论电离波前相互作用的理论和实验进展情况。超短脉冲强激光可以使气体在极短时间内完全电离而形成相对论运动的电离波前,电磁波探针与该波前相互作用会导致频率上移,利用这种特性可能实现一种新的大范围激光调谐机制。     

碲镉汞雪崩光电二极管的发展

雪崩光电二极管(APD)工作在足够的反偏下,光生载流子到达耗尽区并诱发放大过程.碲镉汞(MCT)电子和重空穴有效质量之间的非对称性会产生不相等的电子电离系数和空穴电离系数,提供一个由单独一类载流子诱发的碰撞电离过程,从而形成具有包括接近无噪声增益在内的“理想”APD特征的电子雪崩光电二极管(EAPD).对于包括低光子数...     

线性扫频激光器实时动态相频噪声特性研究

基于120°相差干涉和光场相位实时重构的窄线宽激光动态噪声特性测试方法,从时域频率调谐函数、频域频率噪声功率谱密度及其随时间的演化特征等方面,研究线性扫频激光器在不同扫频方式下动态相频噪声的细节特性。实验结果表明,扫频机理或参数差异导致结果呈现完全不同的实时动态噪声特性。电光调制能够在反馈锁相环辅助下获得最佳的扫频线性度,但会引起反馈谐振峰等噪声恶化,其控制参数不同,反馈谐振峰频率等特征也会发生变化;声光调制呈现最小程度的噪声恶化;压电调谐扫频线性度较差,且会附加较大的调谐噪声。该结果为激光器扫频机制及控制技术的研究和工程应用光源选型提供了参考。     

返回散射电离图处理方法研究

提出了一套完整的返回散射电离图处理方法。该方法首先利用信号与干扰的特性对电离图进行干扰去除,并对去除干扰后的电离图进行内插;其次针对电离图的特点进行噪声去除,并根据电离图的距离和频率相关性进行补偿,最后提取前沿。处理结果表明,该方法实时性好,处理效果明显。     

返回散射扫频特殊电离图的信息提取

根据返回散射电离图中噪声和干扰的时统特性提出了一套算法,用于特殊状态下(强底噪、D层吸收增强)的返回散射电离图有效信息的提取。算法首先利用频率域滤波技术,采用巴特沃斯低通滤波器对图像进行过滤处理,使得同频干扰信息得到抑制,然后利用矩形窗去噪和自适应中值滤波器对电离图进行去噪处理,并且对处理后的电离图进行补偿,得到了返回散射电离图干净有效的信号区域,并利用返回散射电离图频率和距离的相关性,将前沿描迹给出。结果显示,该算法对返回散射特殊电离图中的信号部分提取有较好的效果。     

Burg算法在雷达测速中的应用

为将Burg算法应用在汽车测速中,在多普勒效应原理的基础上,推导出移动物体发射波频率与接收波频率之间的关系,并分别用直接法和Burg算法估计测速模型中发射波频率82 Hz与接收波频率81 Hz。经Matlab仿真表明：直接法估计的发射波与接收波主频率分别接近于82 Hz和81 Hz,但频率主峰旁边存在大量噪声频率的假峰;Burg算法估计出的发射波与接收波主频率更准确,同时主峰清晰且较其他噪声频率突出明显。故Burg算法对间隔不大的发射波与接收波的频率分辨力远远优于直接法,可应用于测速环境中。     

FSK-DWDM四波混频的研究

考虑到DWDM系统中的比特序列的随机性、信道间脉冲走离效应等因素的影响。给出了调制格式为FSK,信道为非简并,入射脉冲为啁啾高斯脉冲波情况下的四波混频噪声标准差的理论计算模型,在考虑到多个信道对于探测信道的影响的情况下用实例对其进行分析。研究结果表明在讨论调制偏移频率与四波混频噪声标准差的关系中我们发现调制偏移频率是有最优取值的,特征宽度值的大小基本不会影响到最优取值的选取,但是较小的特征宽度值可以得到比较小的四波混频效应,然而群速度色散值的大小对于调制偏移频率与四波混频标准差的关系曲线图的影响较大,其绝对值在很小的情况下,调制偏移频率与四波混频标准差曲线图基本呈线性增长趋势,随着其绝对值的增大,曲线出现了起伏变化。     

C_3分子线在激光场中的含时密度泛函理论研究

运用将含时密度泛函理论(TDDFT)和分子动力学相结合的方法,研究了C3分子线的光吸收谱以及它在强激光场中的电子和离子响应。计算结果表明,C3分子线光吸收谱可以分为两个区域,其中既包含独立的峰,又包含连续分布的峰。对C3分子线在激光场中的研究表明,在激光强度、极化方向及脉冲长度相同的情况下,当激光频率远低于共振频率时,分子的电离发生较晚而且电离较弱,分子沿激光极化方向的偶极矩与激光脉冲波包很相近,分子激发处于线性响应区;当激光频率处于共振频率范围时,C3分子线的电离增强,而且偶极矩的激发与激光脉冲波包完全不同,与分子的电离密切相关。     

Miniature Nd:YAG lasers: noise and modulation characteristics

The frequency and intensity noise spectra, as well as the frequency modulation (FM) response, of 1320-nm laser-diode-pumped miniature Nd:YAG ring lasers have been measured. The frequency noise spectrum has a resonance peak at the relaxation oscillation frequency of the laser (between 123 and 150 kHz) and is flat beyond 200 kHz with a spectral density of 613 rad²-Hz, much smaller than that of semiconductor lasers; the corresponding laser linewidth is less than 49 Hz. The relative intensity noise is -140 dB/Hz at the valley and has a resonance peak at the relaxation oscillation frequency of the laser. The FM response is flat from DC to 110 kHz and is in the 0.65-3 MHz/V range; the modulation frequency is limited by the relaxation oscillation frequency of the laser     

Parasitic element influence on the wide-band electrical noise and modulation response of semiconductor lasers

The influence of parasitic elements on the wide-band electrical noise in GaAlAs BH-BOG lasers is investigated theoretically and experimentally. The results show that the maximum small-signal modulation bandwidth can be determined from measurements of the electrical noise spectrum. A small difference of the peak frequency in the optical intensity noise and the peak frequency in the electrical noise spectra is observed (about 200 MHz), and it is explained by introducing the nonlinear intrinsic diode impedance in the parasitic element model. However, the peak frequency in the small-signal modulation response spectrum coincides with the peak frequency in the electrical noise spectrum. It is also shown that the spectral line width, calculated from electrical noise measurements, is not significantly affected by the parasitic element filtering. The electrical noise level is observed to approach an inverse output power dependence at high pumping rates, in good agreement with theoretical calculations.     

基于谱估计的噪声调频信号检测方法研究

对干扰信号的频谱特征进行精确测量和分析是实施有效的电子反干扰(ECCM)的重要步骤.通过对噪声调频干扰信号的频谱特征分析,提出采用合适的功率谱估计方法来检测噪声调频信号的主要频谱特征参数.利用MATLAB/Simulink仿真软件分别建立了噪声调频信号源和谱估计方法的系统模型,研究了系统采用不同的谱估计方法和参数设置的情况下所能够达到的检测精度,并根据仿真结果分析比较了不同谱估计方法的性能.     

Analytical modeling of flicker and thermal noise in n-channel DG FinFETs

A compact physics-based thermal and flicker noise model has been developed for n-channel Double Gate FinFETs with varying structural parameters. The effects of mobility degradation due to velocity saturation, carrier heating and channel length modulation have been incorporated for an accurate modeling of noise. The mobility fluctuations dependent on the inversion carrier density have been considered and a characteristic of the flicker noise different from that of Bulk MOSFETs was observed. This has been validated by the experimental results. Based on the proposed thermal and flicker noise model, a compact expression of the corner frequency has been derived and the effects of the structural parameters such as the length and the thickness of the channel have been analyzed. Finally, the model has been applied for p-channel devices and noise behavior in accordance with experimental data has been obtained.     

正态频率调制降低开关变换器电磁干扰的研究

利用正态频率调制技术从噪声产生源头上降低了开关变换器的电磁干扰。简单地分析了具有不变概率密度分布的离散随机信号频率调制降低开关变换器EMI噪声的原理,并试制了一台正态频率调制开关变换器电源样机。给出了开关管电流信号的频谱以及传导干扰测试的结果。实验结果表明该技术能有效降低开关谐波峰值,使开关变换器易于通过EMI测试,具有应用的前景。     

Interferometric noise reduction through intrabit frequencyevolution of directly modulated DFB lasers

A new technique is demonstrated that improves the performance of optical networks subject to interferometric noise. Every transmitter comprises a selected DFB laser that is NRZ ASK directly modulated with a large modulation depth. Under modulation, the center frequency of the DFB laser is found to vary over the duration of each bit, falling during mark bits and rising during space bits with an exponential-like dependency of characteristic time constant ~20 ns. The optical frequency at the midpoint of each bit interval is not constant but depends upon the sequence of the preceding bits. Therefore, on the interference of a delayed-replica parasitic crosstalk waveform the interferometric noise generated on detection may be reduced by RF filtering according to the difference in center frequency of the interfering bits. This noise suppression which requires no additional hardware has been successfully modeled and experiment demonstrates little performance gain for a single interferer, as predicted. However, in the presence of multiple interferers significant improvement is predicted and observed at sub-Gb/s rates     

Hybrid mode-locking of an angled-stripe C3laser

An antireflection-coated angled-stripe two-section C3laser has been mode-locked in an external cavity by application of sinusoidal modulation at the cavity round-trip frequency to the section providing gain while the other section provides saturable loss. Pulses less than 20 ps in duration with low noise and background intensity are obtained subject to the relaxed operational tolerances characteristic of hybrid mode-locking.     

Adaptive noise mitigation based on peak estimate and feedback compensation in power line communication

According to the problem that the threshold for traditional blanking depends on the characteristic parameters of noise and exist large deviation,an adaptive noise mitigation algorithm based on peak estimate and feedback compensation(ANMPEFC)in power line communication was proposed.First,SLM mapping preprocessing method was employed to reduce the PAPR of emission signal,peak information was used to estimate the frequency of the received signal and the relationship between peak frequency and impulse characteristics was established.Next,received signal was processed by blanking block and feedback compensation block adaptively according to estimated pulse frequency.Finally, performance of proposed algorithm and existing algorithms were analyzed based on threshold deviation.According to the results from simulation,it is clearly demonstrated that the proposed ANMPEFC can work in power line impulse noise environment without knowing the noise characteristics and has better performance in contrast to existing impulse noise suppression algorithm.     

基于Wigner-Hough变换和中值滤波的加速度估计

当雷达发射脉冲个数比较少、噪声方差比较大时,单独使用Wigner-Hough变换(WHT)估计目标径向加速度时会有较大的误差,针对这一问题提出一种Wigner-Hough变换和中值滤波相结合的估计加速度方法,首先研究了相参脉冲回波信号Wigner-Ville分布(WVD)特点,讨论了谱峰位置与瞬时频率的关系,然后采用Hough变换和中值滤波方法时Wigner-Ville分布(WVD)峰值信息进行处理来提取信号的调频率,最后根据加速度估计公式估计出目标加速度,最后进行了仿真验证,在不同积累脉冲个数和信噪比条件下证明了该算法的有效性.     

光纤CATV中调相法抑制相位干涉噪声的研究

本文从理论上研究了附加相位调制抑制相位干涉噪声的方法 ,研究表明 :在光纤AM CATV外调制传输系统中 ,对传输光载波信号引入附加相位调制 ,当相位调制信号的频率为CATV频带的两倍以上时 ,可以有效地抑制相位干涉噪声的发生 ,抑制程度与相位调制度有关。