Optimized three-dimensional lenses for wide-angle scanning

Three-dimensional bootlace lens antennas with two and four focal points can be optimized to produce high-quality scanned beams over a wide field of view. For two-dimensional scanning, the planar feed locus is replaced by a curved feed locus designed to minimize path length errors. Comparisons with previous bootlace lens designs demonstrate the advantages of this focal distribution. The bifocal lens shows good scanning performance in both principal and orthogonal planes. The quadrufocal lens performs better in its principal plane than in its orthogonal plane. It is also shown that the quadrufocal lens can be realized with a planar outer surface and a circular focal arc, and improved scanning performance is still achievable. Further optimization of the focal arc and/or relaxation of the planar outer surface condition results in quadrufocal lenses with negligible phase errors in the principal plane.     

Design considerations for two-dimensional symmetric bootlace lenses

It is generally known that a symmetrical bootlace lens having two pairs of conjugate foci can be designed. Additionally, there is a bootlace lens, the R-2R, which focuses perfectly at infinitely many points. It is shown in this paper that the R-2R is unique; there are no other perfect bootlace lenses and, in fact, no others with more than two pairs of conjugate off-axis foci.     

高斯光束通过两种球差透镜的聚焦特性比较

通过研究,比较了高斯光束通过两种不同球差透镜的聚焦特性。研究表明,高斯光束通过球差透镜的聚焦特性由球差透镜的类型、球差大小和光束的菲涅耳数共同决定。不同的球差透镜要实现无焦移聚焦和越过焦点的聚焦的条件是不同的。     

变焦鱼眼镜头系统设计

变焦鱼眼镜头系统具有更大的视场角、更大的相对孔径、更大的反远比的特点。文中的设计过程中,首先,利用平面对称光学系统理论设计了固定焦距的鱼眼镜头初始结构;然后,把此鱼眼镜头的组元划分为前变焦组和后变焦组两个变焦组,并利用了高斯光学理论对整个变焦镜头进行了变焦优化;最后,得到一成像质量良好的变焦鱼眼镜头。该镜头最短焦距8 mm时的视场角为180°,最长焦距16 mm时的视场角为90°,其相对孔径为1/3.5。设计结果表明:该变焦鱼眼镜头系统的调制传递函数（MTF）数值在不同的焦距长度、空间频率为50 lp/mm时均不低于0.45,该变焦鱼眼镜头物镜比其他变焦鱼眼镜头具有更好的成像质量。     

高斯光束经过球差环形透镜的聚焦

本文讨论高斯光束经过球差环形透镜的聚焦。推导并得到了聚焦光场轴上点的光强分布的表示式。并对其进行数值计算。数值计算结果表明,对于负球差的情况下,得到的光强的最大点位置（最佳聚焦点）相对于无球差情况,往透镜方向移动,即焦移增大;并且,最佳聚焦点的光强较无球差时大,当球差环形透镜的中心拦截比ε取一定值时,得到的轴上点光强最大值远大于无球差时的光强最大值。此外,当透镜具有正球差时,聚焦光场的光强最大点（     

Compound Fresnel Zone Lens Conformal to Truncated Cone: Antenna Application

A millimeter wave antenna consisting of two Fresnel zone plate lenses, plane and conical, is examined numerically by use of the vector diffraction theory. The lenses are of Wood-Wiltse (double-dielectric) or Soret (half-open) type, and are designed for the frequency of 117 GHz. The lenses are made conformal to a truncated circular cone with a base diameter of 500 mm and a plateau diameter of 250 mm. Designs for two opening semi-angles, 45° and 75° each of them with a particular lens thickness are presented. For the angle of 90° the cone lens becomes a plane ring lens, which in combination with the plateau zone lens forms a plane lens of size equal to the cone base diameter. Illuminated by directive feeds set at a focal distance of 525 mm from the cone apex, the double-dielectric and half-open compound and plane lenses, form three pairs of Fresnel zone lens antennas, the co-polar and cross-polar radiation characteristics of which have been compared numerically. The double-dielectric lens antennas examined are about 5 dB superior in gain to the half-open lens antennas, which has a gain of approximately 45 dBi. Because all lenses are of equal transverse aperture, the corresponding lens antennas exhibit the same ?3 dB beamwidth of about 0.33 degrees. The plane zone lens antenna is very thin and simple. Instead, the antenna comprising a 3-D compound Fresnel zone lens is thicker but can be made conformal to a specific surface shape and possesses more levels of design and optimization freedom.     

静电圆锥透镜曲轴电子束聚焦理论的研究

在曲轴宽电子束聚焦理论的基础上，本文研究了静电圆锥透镜聚焦性质，提出了静电场中考虑主轨迹为平面曲线情况下电子束的焦点、焦距等电子光学基本参量的定义。作为例子，给出了两种类型的静电圆锥透镜的电子光学在不同电参量下的关系曲线。     

Focusing characteristics of curvilinear half-open Fresnel zone plate lenses: plane wave illumination

A diffraction field-focusing equation based on a specific conical-segment linearization procedure is derived for the Fresnel zone plate (FZP) lens of arbitrary curved profile and is applied for contrasting plane, spherical, parabolic and conical zone plate lenses, convex-side illuminated by a paraxial plane wave front. Two sets of 100-GHz curvilinear and plane FZP lenses are studied numerically with regards to their dimensions, axial focusing intensity and footprint, and frequency bandwidth. For the first set , where the curvilinear and plane lenses share a common lens base aperture and have equal focal lengths, the following new finding has resulted: regardless of their different in shape profiles the FZP lenses have equal zone numbers and produce similar axial focusing. The second set also consists of plane, spherical, parabolic and conical lenses. They share a common apex, and have equal in diameter base apertures and focal lengths but different thicknesses. For such disposition and proportions, the FZP lenses possess different zone numbers and focusing parameters (gain, efficiency, footprint and bandwidth). The belief that the curvilinear FZP have superior (or inferior) electromagnetic characteristics, compared to those of the plane FZP lens with equal number of zones is not in general true. Their relative focusing qualities can vary significantly depending on the lens positioning and dimensions.     

An equal group delay waveguide lens

Analytical and experimental results are presented on a circularly polarized waveguide lens that has much greater bandwidth than conventional waveguide lenses. This is achieved by designing the lens to have equal group delay for all rays from the focal point of the lens to the aperture plane. Haft-wave-plate phase shifters in each waveguide element are then oriented to produce a planar phase front. This results in a lens whose aperture phase distribution remains essentially constant over a much wider frequency range than in conventional waveguide lenses. A comparison with a minimum thickness conventional lens and with a phase compensated (Coulbourn) lens is made. A 46-in X band lens was built and tested over a frequency range from 7-9 GHz to confirm the bandwidth performance.     

中波红外光学补偿三视场光学系统

针对320×240元致冷型凝视焦平面阵列探测器,设计了一种中波红外光学补偿三视场光学系统。该系统由变 焦物镜系统和二次成像系统构成,包括8块透镜(引入3个高次非球面,其余均为球面),并采用两个反射镜折叠光路。利用光学补偿变焦 原理和光学设计软件给出了系统的光学外形结构图,并对其像质和工艺性进行了分析。该系统可以通过对一组透镜的轴向定点移动实现 20°×15°、3.5°×2.6°和1.3°×1°三个视场的切换,系统变倍比为 1∶15。各视场在16 lp/mm空间频率处的光学传递函数(MTF)值均大于0.5,弥散斑直径的均方根(RMS) 值均小于20 m。工作波段为3.7 ～ 4.8 m,满足100 %冷光阑效率。该系统结构紧凑,工艺性好,成像质量高。     

Wide-angle microwave lens for line source applications

A new "time-delay" scanner consists of a constrained wide-angle two-dimensional microwave lens with a straight front face in which lens elements connect arbitrary points on the inner and outer contours. The lens can operate at very short pulse lengths and can scan more beamwidths than any previously known device of its type. A phase analysis shows that this design has very small coma aberrations and that the lens can generate fractional degree beams. Criteria developed for selecting optimum lens parameters are given. The radiation patterns of an experimental model in which the lens elements consist of coaxial cables show the expected wide-angle characteristics. In further tests incremental scanning was obtained through the use of phase shifters in the coaxial lens elements. The design of symmetrical three-dimensional lenses is briefly discussed. A table of lens contour parameters is given for an optimum lens design with scan anglealphaof30deg.     

衍射微柱透镜轴向光强分布特性的严格电磁分析

衍射聚焦器件轴向光强分布的焦深和焦移特性，直接决定着系统接收面的装配误差和获得最佳的能量利用率。当器件的口径和面型特征尺寸可与照射波长比拟时，必须考虑光波与衍射器件的电磁作用。利用严格电磁分析方法——时域有限差分法，对有限口径衍射微柱透镜的轴向光强分布进行了严格分析，并且与传统的标量分析方法进行详细比较。分析比较了TE和TM极化波入射情况下，不同面型分布(8台阶，16台阶量化面型和连续面型)的衍射微柱透镜焦深和焦移特性与透镜F数的关系。结果表明透镜轴向光强最大点向透镜面偏移，焦移量的严格计算结果要大于标量计算结果，表明透镜的快聚焦特性，而二者得到的焦深量基本一致，同时两种理论方法都表明透镜焦深和焦移随F数的增加而增加。     

面阵探测器连续扫描成像光学系统

研制了一套用于面阵探测器360连续扫描成像的红外光学系统。该光学系统包含了一个无光焦度的望远镜、一个方位补偿摆镜及一个二次成像物镜,采用了制冷型面阵红外探测器。引入了方位补偿摆镜,按二倍角关系朝相反方向摆动,解决了面阵探测器连续扫描中的成像拖尾与模糊问题。采用了像方扫描方式,使得摆镜通光尺寸由物方扫描的大约40 mm220 mm缩减至目前14 mm22 mm,摆镜质量减轻了95%以上,摆动频率可达100 Hz,使系统可在1 s内完成对360方位的扫描成像。系统结构简洁紧凑,共由八片透镜以及一片反射镜组成,像质接近衍射限。实验室测试结果表明:方位补偿摆镜固定时,对小圆靶成像有明显拖尾成长条状;而开启摆镜摆扫之后,小圆靶成像清晰无变形,成像效果接近凝视型。     

平顶多高斯光束通过ABCD光学系统的传输特性

利用广义惠更斯一菲涅耳衍射积分公式,研究了平顶多高斯光束通过ABCD光学系统的传输特性,推导出光强分布的解析式.以透镜系统为例,给出了平顶多高斯光束聚焦场轴上的和焦面处的光强分布表达式,并对其光强分布进行数值计算及分析.研究结果表明,平顶多高斯光束的聚焦特性与阶数N以及透镜系统的菲涅耳数Nw等有关,随着平顶多高斯光束的阶数N的增大或透镜系统的菲涅耳数Nw增大,轴上和焦面上的光强迅速增大、聚焦光斑减小、焦移量迅速减小.     

采用非制冷红外探测器的折衍混合物镜设计

针对长波320×240元非制冷焦平面阵列探测器,设计了折射／衍射混合大相对孔径红外镜头,工作波段8～12舯,焦距为90mm,F数为1,视场为10°．系统为三片式结构：利用二元光学元件具有大的负向色散特性,在第4面引入衍射面,有效地消除了色差,简化了系统结构并减轻了质量,并用ZEMAX光学设计软件进行了像质评价．结果表明,系统成像质量良好,各项指标均满足使用要求．     

利用球差透镜获得超衍射极限聚焦

从ＨｕｙｇｅｎｓＦｒｅｓｎｅｌ衍射积分公式出发,得到了高斯光束经过球差透镜聚焦之后聚焦光场的光强分布的表示式。数值计算结果表明,当透镜存在负球差时,可获得超衍射极限聚焦,即得到的聚焦光斑比高斯光束经过无球差透镜聚焦而得到的聚焦光斑还小。并且,透镜的负球差系数越大,得到的聚焦光斑越小。相反,当高斯光束经过正球差透镜聚焦,得到的聚焦光斑比无球差时大。透镜的球差系数愈大,得到的聚焦光斑愈大。讨论了透镜的球差对轴上光强最大点（最佳聚焦点）的影响。     

Resolution of Near-Field Microwave Target Detection and Imaging by Using Flat LHM Lens

It is demonstrated in this paper that higher focusing resolution will be provided by flat left-handed metamaterial (LHM) lens if compared to convex dielectric lens and elliptical reflector focusing system. High-resolution near-field microwave target detection and imaging with flat LHM lens can be implemented by scanning the focal point of the flat LHM lens in the region under detection and screening directly the field intensity distribution of backscattered microwave refocused by the flat LHM lens. Numerical simulations demonstrate that sub-wavelength imaging resolution can be obtained by the proposed approach due to the sub-wavelength focusing resolution of flat LHM lens. Moreover, almost unique imaging resolution for the detection and imaging of target at different depths is also demonstrated. For practical LHM lenses, it is shown that the losses of LHM up to the order as reported in some LHM experiments will limit the sub-wavelength resolution of the proposed approach to an acceptable level.     

透镜组Fourier变换特性及集成化光学系统的进一步修正

采用系统论的方法对透镜组的Ｆｏｕｒｉｅｒ变换特性进行了理论推导，并依据理论结果对通过附加一个相位补偿透镜的方法来缩短光学４ｆ系统总长度的光学系统所采用的厚相位补偿透镜的焦距进行了修正，从而提高了超短光学系统Ｆｏｕｒｉｅｒ变换的精度。在一般情况下采用两个透镜组替代了系统中两个单片Ｆｏｕｒｉｅｒ透镜，短光学系统的总长度可缩短为原来的四分之一以上。从而为光学系统的集成化奠定了良好的基础。     

大相对孔径变焦红外光学系统无热化设计

随环境温度变化红外镜头会产生热离焦现象,一般定焦红外光学系统可通过多种红外材料组合或引入衍射面来实现光学被动式无热化设计,而变焦红外光学系统大多是通过移动透镜组来实现机械主动式无热化设计。文中根据光学变焦原理和光学被动式无热化原理,提出一种变焦光学被动式无热化设计方法,并采用该方法设计了一种大相对孔径双视场无热化长波红外光学系统。该系统焦距为25/50 mm（变倍比为2:1）,工作波段为8~12 μm,F数为0.9,可匹配640×512,像元为17 μm×17 μm的非制冷红外焦平面阵列探测器。光学设计中采用3种红外光学材料（硫系玻璃HWS6、硒化锌和锗）组合,并引入3个偶次非球面,实现变焦无热化设计。设计结果表明:该系统在宽温度范围内具有良好的成像效果和温度自适应性,在空间频率30 lp/mm处,-50℃~80℃温度范围内各视场MTF均大于0.3。该红外光学系统结构简单、工艺良好,在红外车载领域有着广泛应用前景。     

Through a lens sharply [FluidFocus lens]

Philips Research Laboratories has developed the FluidFocus lens that is ideal not only for camera phones but also in products whose design constraints demand a tiny but capable optical system. Like the lens of the human eye, the FluidFocus lens varies its focus by changing shape rather than by changing the relative positions of multiple lenses. The lens uses electrostatic forces to alter the shape of a drop of slightly salty water inside a glass cylinder 3 mm in diameter and 2.2 mm long. One end of the cylinder points toward the image plane while the other is directed at the subject being imaged. The cylinder containing the water drop is filled with oil. Around the inside walls of the cylinder is a water-repellent Teflon-like coating, and behind this coating is an electrode. Basically, the water and the oil makes up the lens, and the shape of the interface between the two determines its focal length. The optical power of the lens that forms at the surface between the oil and the water depends on the curvature of the meniscus and the difference between the refractive indices of the oil and water.