傅里叶变换轮廓术中相位失真的预矫正方法

介绍了一种基于傅里叶变换轮廓术的三维面形测量系统中相位失真的预矫正方法。由于投影系统和成像系统的空间三角位置关系、投影仪的发散照明和两套系统蕴含的光学畸变,投影一幅相位与空间坐标成理想线性关系的标准正弦光场,拍摄到的条纹相位和空间坐标不再呈线性分布,引起相位失真,甚至会影响系统测量精度。该方法借鉴反向条纹投影的思想,计算拍摄光场的非线性相位分布与理想的线性相位分布之间的关系,预先矫正,反算出一个新的待投影光场。实验结果表明这种方法能有效地减小该类相位失真所导致的测量误差,获得了更好的测量结果．     

阿秒脉冲产生和测量技术研究进展(特邀)

阿秒脉冲光源诞生于21世纪初,是同时具有阿秒时间和纳米空间分辨率的全相干光源,在近20年的时间里,推动了阿秒科学研究不断取得显著的进展和突破。阿秒脉冲为物理、化学、生物、材料、信息等领域的发展提供了全新研究手段和重要创新机遇。本文介绍了阿秒脉冲的重要发展历程,主要综述并总结了高次谐波、阿秒脉冲产生以及阿秒脉冲测量的关键技术和现状,最后对阿秒脉冲研究的发展进行了展望。     

评析217——函数的近似图象应反映函数的基本性态

问题至截稿时止共收稿22篇.来稿一致认为原解法2正确,解法1错误,错误的原因是解法1所绘图象失真,错误地表现了函数的性态.函数g(x)=ln/x在[1/e,e]上的图象应是上凸的,而解法1中的图象却画成了先下凸再上凸(存在拐点),导致虽思路正确,但结果错误.当然也可用几何画板等作图.这启示我们:在利用数形结合思想解题时,虽然我们画出的只是函数的大致图象,但不能太随意,要     

Regularity of the inverse of a homeomorphism with finite inner distortion

Let f:Ω→ f(Ω) R~n be a W~(1,1)-homeomorphism with L~1-integrable inner distortion.We show that finiteness of min{lip_f(x),k_f/(x)},for every x ∈Ω\E,implies that f~(-1) ∈ W~(1,n)and has finite distortion,provided that the exceptional set E has cr-finite H~1-measure.Moreover,/ has finite distortion,differentiable a.e.and the Jacobian J_f 0 a.e.     

基于十倍光学拉伸的5GHz微波信号模数转换研究(英文)

利用光学时间拉伸法对微波信号进行降频处理,提高了后端电子模数转换器的有效模拟带宽和有效采样速率.设计了一套对5GHz微波信号十倍降频的光学时间拉伸模数转换系统.对色散导致的信号功率损耗特性以及调制引起的谐波失真进行了理论分析和数值仿真,结果表明:当系统带宽为5GHz时,光学时间拉伸引入的信号噪声失真比不会劣化后续电子模数转换器的有效位数,该模数转换系统的有效模带宽可达8GHz,有效采样率为200GS/s.     

运用多目标规划优化功放的预失真模型

预失真技术是克服功率放大器非线性失真的一种非常有效的方法.许多研究者从数学建模的思想角度出发,建立了关于功放与预失真的各类级数模型,以实现线性增益输出.但是在应用通信系统中,这些模型不能有效地动态实现功放效率尽可能高的要求.在和记忆多项式模型的基础上,创新地运用多目标规划的方法优化功放的预失真模型.在满足一定的线性化输出的同时,尽可能地得到更高的功放效率,而且能同时计算出增益系数与模型参数.对于数据量为1000的无记忆功放得到增益倍数为1.82649,预失真模型的NMSE值为-41.5633.数据量为73920的有记忆功放得到增益倍数为9.5969,预失真模型的NMSE值为-24.3682.     

Role of excited states in the elliptically polarized harmonic generation

We theoretically investigate the contribution of the excited state to the ellipticity of the harmonics from H＋ at different orientation angles irradiated by a linearly polarized laser pulse. It is found that the first excited state has a significant influence to the ellipticity of the harmonics, and the contribution of higher excited states to the ellipticity can be neglected. Moreover, the conclusion is not dependent on the laser intensity.     

Application of wavelet-based active magnet power supply filter in accelerator

Since modern accelerators demand excellent stability to magnet power supply （PS）, it is necessary to decrease harmonic currents passing magnets. Aiming at depressing the rappel current from the PS in the Beijing electron-positron collider Ⅱ, a wavelet-based active power filter （APF） is proposed in this paper. An APF is an effective device to improve the quality of currents. As a countermeasure to these harmonic currents, the APF circuit generates a harmonic current, countervailing harmonic current from PS. An active power filter based on wavelet transformation is proposed. Discrete wavelet transformation is used to analyze the harmonic components in the supply current, and an active power filter circuit works according to the analysis results. Our simulation and experiment results are given to prove the effect of the APF.     

Joint nonlinear electrical equalization in coherent optical PDM DFT-spread-OFDM systems

We propose a joint nonlinear electrical equalization approach in coherent optical discrete-Fourier-transform spread orthogonal-frequency-division-multiplexing(DFT-spread-OFDM) systems with polarization division multiplexing(PDM).This method is based on an adaptive Volterra series expansion for nonlinear distortions of two orthogonal polarizations.The nonlinear electrical equalization is validated through numerical simulation of 100-Gb/s quadrature phase shift keying and 200-Gb/s 16 quadrature amplitude modulation PDM DFT-spread-OFDM systems.     

All-optical broadcast and multicast technologies based on PPLN waveguide

All-optical 1 ×4 broadcast and 1 ×3 multicast experiments of a 40-Gb/s return-to-zero on-off keying （RZ- OOK） signal based on a periodically poled lithium niobate （PPLN） waveguide are demonstrated in this letter. Clear opened eye diagrams and error-free performance are achieved for the broadcast signals at 1541.3, 1543.7, 1548.5, and 1550.9 nm. Multicast technology uses cascaded second-harmonic generation and difference-frequency generation in a Ti：PPLN waveguide. An error-free operation with a negligible power penalty is achieved for the three wavelength-division multiplexing multicast signals at 1533, 1537, and 1541 nm.