低阶模式校正自适应光学系统的补偿效果分析

引入规格化的相位谱「不一定为科尔莫戈罗夫（Ｋｏｌｍｏｇｏｒｏｖ谱」,推导了大气湍流相位结构函数、低阶模式校正后的残余相位结构函数以及长曝光光学传递函数（ＬＴＦ）。分别给出了在各种不同大气湍流强度ρ０,不同相位谱空间频率的指数下降因子ρ时,大气湍流相位波前低阶模式完全校正后和倾斜部分校正时的长曝光光学传递函数（ＯＴＦ）、长曝光斯特列尔（Ｓｔｒｅｈｌ）比和半高全宽（ＦＷＨＭ）的数值计算结果。     

激光导引星大气湍流波前非等晕性误差的像差模式分解

激光导引星概念解决了自适应光学技术的信标问题，同时带来了无法克服的非等晕性误差。将高度聚焦非等晕性误差和角度等晕性误差统一起来考虑，分析激光导引星的大气湍流波前各阶模式的非等晕性误差，并给出了解析模型。同时分析了瑞利导星和纳导星的大气湍流波前的模式非等晕性相对误差，在没有角度偏离的情况下，90km的钠导星的模式非等晕性误差明显小于15km的瑞利导星，但是它对角度的敏感程度却远远大于端利导星。采用激光导引星的自适应光学系统用于大气湍流的校正，选择较低阶的模式校正就可以达到较好的效果，而且即使目标与导引星的偏角大于等晕角，选择低阶模式也可以达到有效的部分校正效果。     

时域分析自适应光学中的非等晕性

本文利用时域分析方法讨论了自适应光学中的非等晕性以及相位梯度法克服非等晕性的适用性,并将位相补偿和位相梯度法补偿情况下的剩余位相结构函数和Strehl比的一般表达式,统一用传递函数H(f)来描述。该关系式不仅可分析非等晕性,同时可讨论大气平均风场和系统响应带宽对自适应光学系统补偿效率的影响。     

激光导星角度与聚焦非等晕性综合分析

采用自适应光学(AO)系统对湍流大气进行校正时,非等晕性误差的影响不可避免。基于空间谱滤波技术,围绕湍流大气角度、聚焦、角度与聚焦相耦合非等晕性问题,进行了统一建模,给出了不同情况下的理论描述公式,分析了纯角度和纯聚焦非等晕误差中不同泽尼克模式分量所占比份。针对典型AO系统工作模式,分析了不同高度大气层对非等晕性误差的贡献。实际应用时,根据应用场景,应对AO系统工作模式和信标模式做优化匹配选择。     

自适应光学中的非等晕性

本文讨论了自适应光学中非等晕域对补偿效果的影响,提出了一种减小非等晕性误差的新方法—位相梯度法。分析结果表明,该方法可显著增大有效校正的角范围,使非等晕性误差的影响大大减小。我们预期位相梯度法有望解决自适应光学中信标的非等晕性问题。     

模式耦合对倾斜校正自适应光学系统的非等晕限制

 分析了当入射信标波前与观测目标不在同一方向且考虑模式之间的耦合时,倾斜校正自适应光学系统的波前残余误差。并引入模式耦合因子变量,分析了模式耦合对倾斜校正自适应光学系统波前校正残余误差的影响。此外还给出了光波水平大气传输时的数值计算结果。     

模式耦合对倾斜校正自适应光学系统的非等晕限制

分析了当入射信标波前与观测目标不在同一方向且考虑模式之间的耦合时,倾斜校正自适应光学系统的波前残余误差。并引入模式耦合因子变量,分析了模式耦合对倾斜校正自适应光学系统波前校正残余误差的影响。此外还给出了光波水平大气传输时的数值计算结果。     

自适应光学系统的几何非等晕性

利用横向谱滤波方法给出了研究自适应光学几何非等晕性的一般关系式。在特殊场合,对这些一般关系式进行解析求解,可获得与经典理论一致的结果;一般情况下,则只能求得数值解。以离焦分量也由自然信标子系统校正的特殊激光导星自适应光学系统为例,说明了所述一般关系式在研究自适应光学几何非等晕性方面的应用。     

《光学学报》2003年23卷学科分类索引

文　　　　　题期数起始页自适应光学激光导引星大气湍流波前非等晕性误差的像差模式分解 3 3 4 8两种自适应光学系统中哈特曼波前传感器与变形镜的对准误差 6750自适应光学系统的最优斜率复原算法 6756强湍流效应下不同信标波长的自适应光学校正 12 14 89GaN薄膜的蓝光和红光发射机理研究 12 14 93应用光学液晶实时掩膜技术制作连续微光学元件 2 2 2 0结构光焊缝检测传感器设计理论的研究 2 2 2 5激光输入光纤环形腔内相位调制输出功率谱分析 2 2 3 1折 /衍混合单透镜在目镜中的应用研究 2 2 3 6快速傅里叶算法在哈特曼夏克传感器波前重构…     

多层共轭自适应光学系统中等晕角的计算

介绍了多层共轭自适应光学(MCAO)系统的基本原理及其对提高自适应光学系统的等晕角的作用。介绍了用计算机模拟计算MCAO等晕角所用的数值方法,并给出了相应的算法。计算了在传统的自适应光学系统中的等晕角的大小以及采用多层共轭技术的自适应光学系统的等晕角的大小,并对二者进行了比较,说明了多层共轭自适应光学系统相对于传统的自适应光学系统在提高系统的等晕角方面的优越性。结果表明,在MCAO中,变形镜的个数越多其等晕角越大。     

Optimum deformable mirror modes for sensorless adaptive optics

Wavefront sensorless adaptive optics schemes rely upon the accurate generation of aberration modes by the adaptive element, usually a deformable mirror. Analytic functions are often used for representation of the aberrations in these systems. Such functions cannot be perfectly reproduced by deformable mirrors and the approximation errors can affect the aberration correction procedure. We derive alternative modal basis sets directly from the actuator influence functions, thus avoiding the approximation errors. We investigate how the choice of aberration modes affects the performance of a sensorless adaptive imaging system. The new modes are found to be most advantageous for deformable mirrors with a small number of actuators.     

Modal analysis of the range evolution of broadband wavefields in the North Pacific Ocean: low mode numbers

The results of mode-processing measurements of broadband acoustic wavefields made in the fall of 2004 as part of the Long-Range Ocean Acoustic Propagation Experiment (LOAPEX) in the eastern North Pacific Ocean are reported here. Transient wavefields in the 50-90 Hz band that were recorded on a 1400-m long 40 element vertical array centered near the sound channel axis are analyzed. This array was designed to resolve low-order modes. The wavefields were excited by a ship-suspended source at seven ranges, between approximately 50 and 3200 km, from the receiving array. The range evolution of broadband modal arrival patterns corresponding to fixed mode numbers ("modal group arrivals") is analyzed with an emphasis on the second (variance) and third (skewness) moments. A theory of modal group time spreads is described, emphasizing complexities associated with energy scattering among low-order modes. The temporal structure of measured modal group arrivals is compared to theoretical predictions and numerical simulations. Theory, simulations, and observations generally agree. In cases where disagreement is observed, the reasons for the disagreement are discussed in terms of the underlying physical processes and data limitations.     

自适应光学系统模式控制动态优化方法

像差校正模式项数是自适应光学系统模式控制算法中的一个重要参数,其大小对补偿效果影响明显。通过对系统响应函数矩阵的奇异值分解构建像差模式空间,以不同控制项数下残余像差的均方根估计为依据确定每次校正的模式项数,提出了一种模式项数动态优化的控制方法。以Hartmann-Shack波前传感器和薄膜变形镜为主要部件搭建自适应光学实验系统,通过拟合不同像差验证上述控制方法,实验结果表明,和固定项模式控制方法比较,动态优化方法校正的系统残余像差更低,可明显提高自适应光学系统的空间拟合性能。     

利用水平阵模态域波束形成判别声源深度*

针对近水面声源和水下声源的深度判别问题,根据近水面声源难以激发低阶模态的物理现象,研究利用声源波数谱结构和波数位置的不同来分辨近水面声源和水下声源。通过采用MVDR的谱估计方法进行模态域波束形成,补偿水平阵各阵元之间各号简正波的相位差,获得主瓣窄、旁瓣低的声源信号波数谱。波数谱的波数位置与频率呈近似线性关系,水中声速剖面、海底参数、海深都会影响波数谱的具体结构和位置。此外,声源信号的到达角估计误差同样也会影响波数谱主瓣的位置估计。数值仿真结果表明,在浅海负跃层声速剖面条件下,可利用水平阵模态域波束形成判别声源深度,区分近水面声源和水下声源。     

On the sound radiation of a rolling tyre

The sound radiation from rolling tyres is still not very well understood. Although details such as horn effect or directivity during rolling have been investigated, it is not clear which vibrational modes of the tyre structure are responsible for the radiated sound power. In this work an advanced tyre model based on Wave Guide Finite Elements is used in connection with a contact model validated in previous work. With these tools the tyre vibrations during rolling on an ISO surface are simulated. Starting from the calculated contact forces in time the amplitudes of the modes excited during rolling are determined as function of frequency. A boundary element model also validated in previous work is applied to predict the sound pressure level on a reference surface around a tyre placed on rigid ground as function of the modal composition of the tyre vibrations. Taking into account different modes when calculating the vibrational field as input into the boundary element calculations, it is possible to identify individual modes or groups of modes of special relevance for the radiated sound power. The results show that mainly low-order modes with relative low amplitudes but high radiation efficiency in the frequency range around 1 kHz are responsible for the radiated sound power at these frequencies, while those modes which are most strongly excited in that frequency range during rolling are irrelevant for the radiated sound power. This fact is very essential when focusing on the design of quieter tyres.     

Numerical calculations of modes of optical waveguides with two-dimensional refractive index profiles by a field correction method

Abstact We describe a numerical method devised to calculate the lower-order modes of optical waveguides with two-dimensional transverse index profiles. This method is based on finite-difference approximation of the scalar wave equation and the minimization of the error in the field shape of a mode. The field correction method can be applied to waveguides with large index steps and generates the mode's scalar propagation constant and its field. To test the field correction method, it is applied to a three-layer optical fibre and the results are compared with exact solutions. The error in the calculations of the modal effective indices is found to be of the order of 10^-6. Example mode calculations are given for fused couplers and rib waveguides.     

Virtual sensors for active noise control in acoustic-structural coupled enclosures using structural sensing: part II--Optimization of structural sensor placement

The work proposed an optimization approach for structural sensor placement to improve the performance of vibro-acoustic virtual sensor for active noise control applications. The vibro-acoustic virtual sensor was designed to estimate the interior sound pressure of an acoustic-structural coupled enclosure using structural sensors. A spectral-spatial performance metric was proposed, which was used to quantify the averaged structural sensor output energy of a vibro-acoustic system excited by a spatially varying point source. It was shown that (i) the overall virtual sensing error energy was contributed additively by the modal virtual sensing error and the measurement noise energy; (ii) each of the modal virtual sensing error system was contributed by both the modal observability levels for the structural sensing and the target acoustic virtual sensing; and further (iii) the strength of each modal observability level was influenced by the modal coupling and resonance frequencies of the associated uncoupled structural/cavity modes. An optimal design of structural sensor placement was proposed to achieve sufficiently high modal observability levels for certain important panel- and cavity-controlled modes. Numerical analysis on a panel-cavity system demonstrated the importance of structural sensor placement on virtual sensing and active noise control performance, particularly for cavity-controlled modes.