非约束纯相位空间匹配滤波器设计研究

根据非约束相关匹配滤波器和纯相位匹配滤波器的概念,分析了非约束纯相位匹配滤波器的特性及其在光学相关识别中的应用,并与其他典型纯相位匹配滤波器进行了比较.模拟和实验结果表明,非约束纯相位匹配滤波器具有畸变容限大、相关峰高、算法简单的特点.用于光学相关识别是一种实用的空间匹配滤波器算法.     

水下光束漂移激光图像抗畸变识别

针对水下激光传输存在光束漂移现象,分析了光束漂移图像对光学相关识别的影响和帧间光束漂移图像噪声的不相关性。研究了抗畸变匹配滤波器设计,提出了基于相位匹配的畸变图像共同特征提取,并作为综合鉴别函数子特征的训练样本,设计了抗畸变综合鉴别匹配滤波器,并进行了仿真验证。Matlab仿真结果证明:抗畸变综合鉴别匹配滤波器设计,结合待识别图像随机散射噪声预滤波,可有效提高光学相关识别输出相关峰的峰值-相关能量比值和相关峰鉴别率值。     

匹配滤波器映射编码方法研究

在Vander Lugt 相关器中,预先制作的匹配滤波器是系统能否得到较好的相关识别结果的关键。通常使用的迂回相位匹配滤波器编码法数据利用率不高,相关效果有进一步改进的空间。对基于最小欧几里德距离的映射编码法进行了研究,利用空间光调制器的振幅与相位调制特性进行滤波器编码,通过仿真实验分析了匹配滤波函数幅度因子对相关结果的影响,并与迂回相位编码法的相关结果进行了对比分析。从仿真结果可以看出:匹配滤波函数幅度因子越大,相关峰值越高;当幅度因子达到103时,相关峰值达到最大值;此时,映射编码法的相关峰值接近于迂回相位编码法的2倍。因此映射编码法比迂回相位编码法更有利于相关峰的判别。     

旋转不变振幅位相合成圆谐滤波器

提出了振幅位相合成圆谐滤器用于旋转不变模式识别，该滤波器的振幅是圆谐滤波器的振幅谱加偏移量后的逆函数，位相是圆谐滤波器的位相谱。计算机模拟实验证明，与传统的圆谐滤波器和纯位相圆谐滤波器相比，振幅位相合成圆谐滤波器具有更好的识别能力，能产生更尖锐的相关峰和更大的输出信噪比。     

用于畸变目标相关识别的匹配滤波器设计

针对尺度缩放和角度旋转变化目标相关识别率低的问题,采用优化折中综合鉴别函数方法设计了具有较大畸变容限的匹配滤波器。在匹配滤波器设计时,通过调整相关输出噪声、训练样本平均功率谱密度和训练样本相似度对训练样本平均值的贡献,得到具有带通性质的匹配滤波器。利用单个匹配滤波器对角度旋转0°～30°、尺度变化0～20%的目标进行了相关识别仿真实验。结果表明：这种匹配滤波器相关输出峰尖锐、鉴别力强、畸变容限大,可用于畸变目标的光学相关识别。     

在相位型滤波器的伪随机编码设计中的改进方法

阐述了相位型滤波器的伪随机编码设计中的改进方法：对全复值调制数据随机编码形成双振幅相位型滤波器。与极小欧氏距离最佳滤波器（ＭＥＤＯＦ）相比较，其性能有很大改善。     

三区复振幅光瞳滤波器

利用光瞳滤波器来改变光在焦斑处的分布,是实现光学超分辨的有效途径。由于受到制作上的影响,现有的光瞳滤波器大都是纯相位型或者纯振幅型的。与纯相位或者纯振幅型光瞳滤波器相比较,复振幅型光瞳滤波器能够实现更好的滤波效果。不过由于制作上的困难,影响了复振幅的光瞳滤波器在实际中的应用。为此给出了一种相对容易实现的复振幅型光瞳滤波器,通过计算表明：在横向具有相同的第一零点比和斯特雷尔比下,该复振幅型光瞳滤波器的旁斑强度比优于纯相位型光瞳滤波器50％,并且有效地降低了纯相位型光瞳滤波器的轴向加宽。     

最大平均相关高度滤波算法在畸变目标识别中的应用

为了解决在联合变换相关器上无法识别复杂背景下畸变目标(目标的平面内旋转或尺寸改变)的问题,对其应用最大平均相关高度滤波算法进行畸变目标识别.首先在频域内优化最大平均相关高度滤波器的三个性能控制参量|然后将优化好的最大平均相关高度频域滤波器映射到物空间,得到最大平均相关高度参考模板.作为实例,本文对复杂背景下的军舰和汽车目标进行了光学识别实验,结果表明,当滤波器的控制参量为γ=1,α=0,β=0.1时,得到的MACH参考模板最为清晰,目标产生的相关峰最为尖锐明亮.通过这种方法,在联合变换相关器上能够得到的比例畸变容差为28%,旋转畸变容差为20°,对于超出上述畸变容差范围的目标,相关峰强度逐步减弱,但部分仍然可以识别.改进后的MACH滤波器在畸变目标的探测领域具有很强的优势和良好的应用前景.     

纯相位型滤波器的伪随机编码

阐述了纯相位空间光滤波器的设计中伪随机编码理论、技术与方法。文中亦展示了利用控制编 复数值函数的振幅能够十分有效地改善远场衍射的质量。     

基于背景噪音谱分析的匹配滤波器设计研究

在空间匹配滤波器设计过程中,为抑制输入场景中背景噪音对输出相关平面上相关点的影响,通过比较匹配滤波函数和背景噪音的傅里叶谱,根据两者差值的量级对匹配滤波函数的振幅进行非线性调制,在匹配滤波过程中使设计的空间匹配滤波器对强噪音的傅里叶谱处透过率降低,而尽量保持输入图像傅里叶谱的高透过率,从而增加输出相关平面上的信噪比,实现相关点的正确探测。计算机模拟和实验结果表明：与纯相位匹配滤波器相比其抗噪能力得到较大改善。     

Graphical design of millimeter-wave finline bandpass filters

A very simple yet accurate design procedure for the finline bandpass filters at millimeter wavelengths is presented. The technique enables the geometry of finline bandpass filters to be obtained accurately from simple closed-form equations and curves. Using this graphical approach, various millimeter-wave finline bandpass filters have been designed. Results in V-band (50 to 75 GHz) and W-band (75 to 110 GHz) are presented and indicate a good agreement between the calculated and measured performances.     

On the design and performance of printed-circuit filters and diplexers for millimeter-wave integrated circuits

This paper describes the design and performance of various millimeter-wave printed-circuit filters and diplexers. These components include microstrip/suspended stripline and finline lowpass filters, capacitive-gap and inductive-iris-coupled bandpass filters, spurline bandstop filters, and finline diplexers. State-of-the-art performances from Ka-band (26.5 to 40 GHz) to D-band (110 to 170 GHz) have been obtained. Agreement between the measured and calculated results was also achieved.     

Chebychev Response of Thin Film Optical Filters

The power reflection coefficient (reflectance) of linear, periodically homogenous, isotropic, nonabsorbing stack filters is derived using full wave analysis. The well-known ABCD characteristic matrix is used to assess the spectral response of the stack filters. Adopting this method requires a huge number of matrix multiplications as the number of layers increases. An alternative approach of evaluating the whole matrix is suggested which is shown to save computational time. Band reject response far from ideal characteristics, due to the presence of unwanted ripples surrounding the stopband, is obtained. Equating these ripples without changing the length of the structure is undertaken by varying some design parameters related to the layers constituting the filter. Namely, the index of refraction and the physical thickness of individual layers are used as optimization variables. This process requires evaluating the derivative of the reflectance with respect to each design variable while leaving other parameters unchanged. The sensitivity of the derivatives to various design parameters is also addressed, which is sometimes required in manufacturing multilayered dielectric thin films.     

Analysis of polarization-independent tunable optical comb filter by cascading MZI and phase modulating Sagnac loop

A novel scheme of tunable optical comb filter constructed by cascading a polarization-swapping MZI and a phase modulating Sagnac loop is proposed. The key features of this comb filter design are its polarization-independence and high speed in wavelength tuning. The wavelength tunability can be readily achieved by incorporating an electro-optic phase modulator into the Sagnac loop. In addition, the filter can be made amplitude adjustable as well. The filter will be desirable for multi-wavelength fiber lasers, multi-channel optical signal processing and optical WDM systems.     

Design and performance of millimeter-wave end-coupled bandpass filters

The design and performance of millimeter-wave microstrip/suspended-stripline end-coupled bandpass filters are presented. Filters in Ka-band (26.5 to 40 GHz) and W-band (75 to 110 GHz) using suspended-stripline and microstrip have been designed. Good agreement between the experimental results and those predicted theoretically was observed. Measured passband insertion losses of less than 1 and 0.5 dB have been achieved in W- and Ka-band, respectively. An extremely wideband waveguide-to-microstrip transition with an insertion loss of 0.25 dB over the full W-band is also presented.     

Performance analysis of dispersion compensating optical FIR filters designed using a quasi-analytic synthesis approach

In this paper we investigate the performance of a quasi-analytic synthesis approach for dispersion compensating optical finite impulse response filters. It is shown by eye opening penalty and optical signal to noise ratio penalty calculations that with this method the filters dispersion can be adjusted reliably and with low effort to compensate for a specific amount of residual chromatic dispersion in optical transmission systems. The maximum attainable dispersion is then only limited by the filter order and the free spectral range rather then by optimization problems within the filter design.     

Design of multilayer high-dispersion mirrors using multi-swarm optimization method

Design of high-dispersion mirrors (HDMs) using a proposed multi-swarm optimization method is reported. We design HDMs for Yb:YAG disk oscillator at 1030 nm and ultrashort pulse Cr:YAG laser at 1550 nm. The results show that the optimum group delay dispersion and reflectance can be obtained with optimal number of layers. The proposed optimization method has a fast convergence rate and powerful global search ability and can be utilized effectively for the design of a variety of optical thin film filters.     

Design of an optical filter using photonic band gap material

The article presents a design of an optical filter using Photonic Band Gap (PBG) materials in the visible and infrared region of the electromagnetic spectrum. This idea is based on the famous Kronig-Penny model in the band theory of solids. The suggested filter may work at any range of the wavelength that can be achieved by choosing the appropriate values of the controlling parameters. This structure is also able to pass the light emitted by the Ruby laser and this acts as a monochromator. Also, we have studied the anomalous behavior of refractive index for the structure having alternate layers of air and GaAs.     

Very longwavelength lowpass interference filters

The extension of metallic mesh interference filter techniques to wavelengths longer than 2000 m is discussed. The problems associated with design considerations and removal of leaks is considered in some detail. Successful filters were produced with edges at 6.3 cm^–1 and 4.3 cm^–1. When used in series and with a specific optical system, good rejection of unwanted radiation was achieved.