Highly Efficient Broadband Achromatic Microlens Design Based on Low-Dispersion Materials

Metalenses with achromatic performance offer a new opportunity for high-quality imaging with an ultracompact configuration;however,they suffer from complex fabrication processes and low focusing efficiency.In this study,we propose an efficient design method for achromatic microlenses on a wavelength scale using materials with low dispersion,an adequately designed convex surface,and a thickness profile distribution.By taking into account the absolute chromatic aberration,relative focal length shift(FLS),and numerical aperture(NA),microlens with a certain focal length can be realized through our realized map of geometric features.Accordingly,the designed achromatic microlenses with low-dispersion fused silica were fabricated using a focused ion beam,and precise surface profiles were obtained.The fabricated microlenses exhibited a high average focusing efficiency of 65%at visible wavelengths of 410-680 nm and excellent achromatic capability via white light imaging.Moreover,the design exhibited the advantages of being polarization-insensitive and near-diffraction-limited.These results demonstrate the effectiveness of our proposed achromatic microlens design approach,which expands the prospects of miniaturized optics such as virtual and augmented reality,ultracompact microscopes,and biological endoscopy.

Chromatic and achromatic differences of melanin-and carotenoid-based plumage coloration in five minivet species(Pericrocotus spp.)under conspecific and predator visual systems

Adaptive mate choice has been accepted as the leading theory to explain the colorful plumage of birds.This theory hypothesizes that conspicuous colors act as signals to advertise the qualities of the owners.However,a dilemma arises in that conspicuous colors may not only attract mates,but also alert predators.The"private channels of communication"hypothesis proposes that some intraspecific signals may not be visible to heterospecific animals because of different visual systems.To better understand the evolution of plumage colors and sexual selection in birds,here we studied the chromatic difference and achromatic differences of melanin-and carotenoid-based plumage coloration in five minivet species(Pericrocotus spp.)under conspecific and predator visual systems.We found that either the chromatic or achromatic difference among male or female minivets’plumage was consistently higher under conspecific vision than under predator vision for all five studied species of minivets.This result indicated that individual differences in plumage colors of minivets were visible to the conspecific receivers and hidden from potential predators as a result of evolution under predation risk and conspecific communication.However,males were under a higher risk of predation because they were more conspicuous than females to the vision of a nocturnal predator.

第四代同步辐射光源加速器物理与技术

同步辐射光源是20世纪应用最广泛的高性能X射线源,已成为物理、化学、能源环境、生物医学、先进材料等领域前沿研究的重要工具。进入21世纪,基于电子储存环的同步辐射光源的发展前沿是第四代同步辐射光源(4GLS)。其采用紧凑型的多弯铁消色散结构,可以实现接近甚至达到X射线衍射极限的超低束流发射度,将光源亮度在第三代光源基础上进一步提升2—3个数量级。文章将重点介绍第四代同步辐射光源关键的加速器物理与技术,以及国际范围内第四代同步辐射光源装置的发展情况。

二值振幅型远场超分辨消色差聚焦器件研究

具有远场超分辨聚焦特性、消色差、小尺寸和易加工的光学聚焦器件在光学成像、光学显微和光刻等领域具有巨大应用潜力.本文提出了一种基于光学超振荡基本原理,结合角谱衍射理论和二进制粒子群算法的二值振幅型远场超分辨消色差聚焦器件设计方法.为了验证所提出设计方法,首先针对波长λ_(1)=405 nm,λ_(2)=532 nm和λ_(3)=632.8 nm的径向偏振光对二值振幅型远场超分辨聚焦器件振幅进行优化设计,再对三者振幅分布进行逻辑“与”操作,使其同时含有3个工作波长远场超分辨聚焦的振幅分布信息.仿真结果表明:在3个波长入射条件下相应的峰值半高全宽分别为0.441λ_(1) (0.179μm),0.469λ_(2 )(0.249μm)和0.427λ_(3) (0.270μm),低于阿贝衍射极限,实现了远场超分辨消色差聚焦,且同时聚焦较小的旁瓣比率(<15%).此类器件具有易加工、消色差和超分辨等优点,适用于光学系统微型化、集成化.所提出的设计方法可拓展至其他光学波段,并为相关光学研究领域提供核心聚焦器件.

瑞利判据启发的可见光波段宽带消色差偏振不敏感超构透镜的设计

超构表面作为亚波长结构单元排布而成的新型平面光学元件,可对光场相位、振幅、偏振及频率进行灵活剪裁,为光学元件集成化和小型化提供了强大的支撑平台。超构透镜是超构表面最重要的应用之一,消色差对于超构透镜的成像质量至关重要。然而,受限于超构元胞共振色散及有限共振带宽,超构透镜在偏离设计波段会遭受较大的色差,从而限制了其在多波长或连续宽带器件中的应用。为此,文中基于焦斑分辨瑞利判据(Rayleigh criterion)原理,提出了一种面向可见光波段宽带消色差偏振不敏感超构透镜的新型设计策略。通过采用共轭相位自旋复用设计理论,将面向两边缘波长、高效工作、两尺寸不同、各向异性的TiO_(2)纳米柱(均具备半波片功能)的旋转角度限制在0°或90°,作为一复合超构胞元构建超构透镜。通过两纳米柱之间的色散互补效应,实现了在可见光波段(λ=470~650 nm)宽带消色差偏振不敏感聚焦性能,同时保持了较高聚焦效率。这一工作为宽带消色差超构透镜的设计领域带来了重大进步,并有望在超紧凑芯片级设备中实现潜在应用。

基于二氧化钒的太赫兹可重构消色差超表面透镜

消色差超表面透镜是近期研究热点。由于需同时满足聚焦相位、群时延和群时延色散,目前消色差超表面透镜的设计存在复杂度较高的缺点。基于此,通过引入相变材料二氧化钒(VO_(2),Vanadium Dioxide)为消色差超表面透镜的设计提供新的自由度,并提出了一种基于VO_(2)实现太赫兹可重构消色差超表面透镜的方法。通过切换VO_(2)的状态,可调控超表面单元引入的Pancharatnam-Berry相位,从而使得超表面透镜满足不同频率所需的相位分布,实现消色差特性。为进行验证,设计了一款工作于1.93和2.14 THz的双频可重构消色差超表面透镜,作为对比还设计了一款工作于1.93 THz的单频不可重构超表面透镜。仿真结果表明,设计的消色差超表面透镜可有效消除频率带来的焦距偏移,具有消色差特性。

Crosstalk-free achromatic full Stokes imaging polarimetry metasurface enabled by polarization-dependent phase optimization

Imaging polarimetry is one of the most widely used analytical technologies for object detection and analysis.To date,most metasurface-based polarimetry techniques are severely limited by narrow operating bandwidths and inevitable crosstalk,leading to detrimental effects on imaging quality and measurement accuracy.Here,we propose a crosstalkfree broadband achromatic full Stokes imaging polarimeter consisting of polarization-sensitive dielectric metalenses,implemented by the principle of polarization-dependent phase optimization.Compared with the single-polarization optimization method,the average crosstalk has been reduced over three times under incident light with arbitrary polarization ranging from 9μm to 12μm,which guarantees the measurement of the polarization state more precisely.The experimental results indicate that the designed polarization-sensitive metalenses can effectively eliminate the chromatic aberration with polarization selectivity and negligible crosstalk.The measured average relative errors are 7.08%,8.62%,7.15%,and 7.59%at 9.3,9.6,10.3,and 10.6μm,respectively.Simultaneously,the broadband full polarization imaging capability of the device is also verified.This work is expected to have potential applications in wavefront detection,remote sensing,light-field imaging,and so forth.

Design of broadband achromatic metasurface device based on phase-change material Ge_(2)Sb_(2)Te_(5)

Based on the phase-change material Ge_(2)Sb_(2)Te_(5)(GST),achromatic metasurface optical device in the longer-infrared wavelength is designed.With the combination of the linear phase gradient GST nanopillar and the adjustment of the crystalline fraction m value of GST,the polarization insensitive achromic metalenses and beam deflector metasurface within the longer-infrared wavelength 9.5μm to 13μm are realized.The design results show that the achromatic metalenses can be focused on the same focal plane within the working waveband.The simulation calculation results show that the fullwidth at half-maximum(FWHM)of the focusing spot reaches the diffraction limit at each wavelength.In addition,the same method is also used to design a broadband achromatic beam deflector metasurface with the same deflection angle of 19°.The method proposed in this article not only provides new ideas for the design of achromatic metasurfaces,but also provides new possibilities for the integration of optical imaging,optical coding and other related optical systems.

Large aperture phase-coded diffractive lens for achromatic and 16°field-of-view imaging with high efficiency

Diffractive lenses(DLs)can realize high-resolution imaging with light weight and compact size.Conventional DLs suffer large chromatic and off-axis aberrations,which significantly limits their practical applications.Although many achromatic methods have been proposed,most of them are used for designing small aperture DLs,which have low diffraction efficiencies.In the designing of diffractive achromatic lenses,increasing the aperture and improving the diffraction efficiency have become two of the most important design issues.Here,a novel phase-coded diffractive lens(PCDL)for achromatic imaging with a large aperture and high efficiency is proposed and demonstrated experimentally,and it also possesses wide field-of-view(FOV)imaging at the same time.The phase distribution of the conventional phase-type diffractive lens(DL)is coded with a cubic function to expand both the working bandwidth and the FOV of conventional DL.The proposed phase-type DL is fabricated by using the laser direct writing of grey-scale patterns for a PCDL of a diameter of 10 mm,a focal length of 100 mm,and a cubic phase coding parameter of 30π.Experimental results show that the working bandwidth and the FOV of the PCDL respectively reach 50 nm and 16°with over 8%focusing efficiency,which are in significant contrast to the counterparts of conventional DL and in good agreement with the theoretical predictions.This work provides a novel way for implementing the achromatic,wide FOV,and high-efficiency imaging with large aperture DL.

Broadband achromatic phase retarder based on metal-multilayer dielectric grating

A new achromatic phase retarder based on a metal-multilayer dielectric grating structure is designed using the rigorous coupled wave analysis method and the genetic algorithm.The optimized phase retarder can maintain phase retardation around 90°from 900 nm to 1200 nm,and the maximum deviation is less than 4.5%while the diffraction efficiencies of TE and TM waves are both higher than 95%.Numerical analysis shows the designed phase retarder has a high fabrication tolerance of groove depth,duty cycle and incident angle.This achromatic phase retarder is simple in design and stable in performance,and can be widely used in optical systems.

A Doubly Achromatic Two-magnet Nonuniform Field Bending System of 270° in Deflection

A new doubly achromatic two-magnet beam bending system is described.Itconsists of two nonuniform dipoles separated by a small drift space.Some doublyachromatic relations are derived.The system showed excellent achromatic and focusingproperties and good quality of electron beam with small diameter.Very small diver-gence and axial symmetry were produced at the output of the system.The system isspecially suitable for low energy electron linac beam with large energy spread.

宽频消色散超表面全息成像

针对超表面全息成像技术中存在的工作频段窄、近场成像效率低等问题,本文提出了消色散宽频超表面全息成像优化原理及模型,提出了基于深度图像先验的深度学习网络模型用于单目标的被动式超表面全息图设计,实现了消色散宽频超表面全息成像。数值仿真和实验结果均证明,所设计的全息成像器件可以在9 GHz~11 GHz频段内实现良好的消色散成像效果,在全息成像、宽频功能器件设计等领域具有极大的应用潜力。

基于神经网络的消色差旋转双棱镜反向解算

为了实现基于双棱镜的光电跟踪平台,需要根据光束指向精确求解两棱镜转角。基于非近轴光线追迹法与二步法,利用神经网络拟合了消色差旋转双棱镜角度差值与偏转角之间的关系,并在求解方位角与消色差旋转双棱镜两组棱镜转角的时候,将其中的非线性关系与线性关系分开,利用神经网络对其中的非线性关系进行了拟合,最终得到了消色差旋转双棱镜转角与出射光束指向的数值关系。实验表明,在仅用3层神经网络共20个神经元的条件下,得到了两棱镜旋转角度反向解算值达到了0.0001°量级。

太赫兹大视场宽带消色差超构透镜

基于超构透镜的太赫兹成像系统因紧凑的体积受到广泛关注。现有太赫兹超构透镜仅能实现消色差或大视场成像,需要大视场宽带消色差超构透镜来进一步提升太赫兹系统的成像质量。文中介绍了一种工作在0.3~0.5THz,数值孔径0.707,直径10mm,视场100°的太赫兹大视场消色差硅基超构透镜。该超构透镜采用了二次非球面型相位剖面,减小了轴外像差,实现了大视场;选取了相位和色散满足要求的单元进行布阵,消除了色差。因此,它有望被广泛应用在生物检测、太赫兹成像等领域。

基于相变材料GST与孔径共享宽带宽消色差透镜的设计

提出了在超构透镜结构上采用孔径共享协同操作的方法,根据散单元输出相位与频率呈线性关系,再结合调控相变材料Ge_(2)Sb_(2)Te_(5)晶化率m值,在设定的波段内合理选择散射单元的尺寸,不同波长入射光经过超表面后能产生符合统一焦距要求的相位分布,从而使消色差超透镜的带宽得到相应拓宽,设计了9.5~13μm连续波段内的偏振不敏感消色差超表面透镜。仿真结果表明,消色差超表面在工作波段内的焦距变化为3.57μm,与设定焦距的误差约为4.3%,并且各波长入射下的焦点半峰全宽均达到了衍射极限,聚焦效率超过60%。提出的消色差超表面透镜,为消色差超表面的设计提供了新的思路,促进了相变材料在宽带消色差超表面方面的研究。

盐处理剂流失量、煅烧强度等对消色力的影响研究

向水合二氧化钛中分别加硫酸铝、氢氧化钾、磷酸,根据实际生产的钛矿情况,一般以硫酸铝和氢氧化钾两种盐处理剂组同时加入,弥补煅烧过程中的晶种缺陷,会出现金红石颜料特性,并产生不同的差异。文章主要针对盐处理添加剂流失量及煅烧强度对消色力的影响展开研究。

Dynamic tunable LWIR achromatic metalens comprising all-As_(2)Se_(3) microstructures

In the field of long-wave infrared(LWIR) thermal imaging, vital for applications such as military surveillance and medical diagnostics, metalenses show immense potential for compact, lightweight, and low-power optical systems. However, to date, the development of LWIR broadband achromatic metalenses with dynamic tunable focus, which are suitable for both coaxial and off-axis applications, remains a large unexplored area. Herein, we have developed an extensive database of broadband achromatic all-As2Se3microstructure units for the LWIR range. Utilizing this database with the particle swarm optimization (PSO) algorithm, we have designed and demonstrated LWIR broadband achromatic metalenses capable of coaxial and off-axis focusing with three dynamic tunable states. This research may have potential applications for the design of compact, high-performance optical devices, including those with extreme depth-of-field and wide-angle imaging capabilities.

菱体型相位延迟器对入射角灵敏性的研究

为了清楚地了解菱体型消色差λ/4相位延迟器对入射角i变化的灵敏性随折射率n变化的规律,利用全反射相变公式详细推导出器件对入射角i变化的灵敏性与折射率n的关系式,并做出了理论曲线。可见,随着折射率n的增加,器件对入射角i的变化更加灵敏。结果表明,设计器件时应尽量避免选择高折射率材料。在分析相位延迟量的测量误差时,这个应用也是很有价值的。

大相对孔径紫外成像仪光学系统设计

为解决目前大多数紫外成像仪存在的定位和指向精度差、色差较大、分辨率及光能利用率不足等问题,设计了一款高分辨率的大孔径消色差紫外光学系统。首先,根据电晕放电检测的应用需求,提出了紫外光学系统的总体设计。然后利用熔石英及氟化钙两种材料的不同色散特性,根据改进的双胶合透镜结构设计了一款大孔径的消色差紫外光学系统,并对该系统进行了公差分析。设计的紫外光学系统在全视场全探测范围内点列图均方根直径<0.08 mm,分辨率为20 lp/mm,满足电力行业中对电晕探测的需求。

菱体型消色差延迟器的优化设计

通过对菱体型延迟器件进行优化设计,能够改善其消色差性。根据光在介质表面全反射时发生相变这一原理,分析了一个具有3个全内反射面的菱体型延迟器件,得出了相位延迟δ与全内反射角θ和相位延迟δ与介质折射率n的关系。通过对δ与θ和δ与n的关系分析,显示了扩大材料选择范围的可行性。结果表明,较大的全内反射角的选择有利于改善延迟器件的消色差性。