亚波长衍射微透镜的设计

设计了连续浮雕衍射微透镜和与其等效的二元亚波长衍射微透镜,采用旋转体时域有限差分法对通过计算机辅助设计出的元件进行了严格的矢量分析,给出了各元件在焦平面的场强分布.分析结果表明,本文设计的二元亚波长微透镜对连续浮雕微透镜有很好的等效效果;填充因子的脉冲宽度调制法要优于填充因子的线性近似法;制作相对误差不大时深度误差和宽度误差对微透镜聚光能力的影响不大.     

Tight focusing properties of double-ring-shaped azimuthally polarized beam through annular high numerical aperture

基于Richards-Wolf矢量衍射积分公式,研究了双环角向偏振光束经环状高数值孔径透镜的聚焦特性,推导了双环角向偏振光束经环状透镜深聚焦的光强表达式.根据数值模拟结果,比较了相关参量的变化对深聚焦特性的影响.研究表明:入射光束经环状高数值孔径透镜聚焦后,在焦平面得到了具有广泛应用的亚波长空心光斑,并且入射光束的相关参数和聚焦透镜的数值孔径大小都会影响光束的聚焦特性,使聚焦空心光斑达到亚波长量级;双环角向偏振光束经环状高数值孔径透镜的聚焦以后,在焦平面附近产生了一个更长的焦深(约28倍入射光波长).     

基于亚波长高对比度光栅的波前调控器设计

基于严格耦合波分析法分析了亚波长光栅波前调控的方法,设计了具有凸透镜、锥透镜和闪耀光栅功能的三种亚波长光栅结构,以平面方式制备了具有聚焦和闪耀效果的三种微纳结构波前调控器.计算了不同光栅厚度、光栅齿和光栅槽宽度下的光栅透射率,通过选择合适光栅参数组合,得到三种波前调控器透射率均在97%以上.硅基平面结构与常规结构器件性能相比,平面和常规透镜、锥透镜在聚焦效果上,焦斑的半高全宽近似相等,峰值强度提高了1.64和2.35倍;平面相对常规闪耀光栅的峰值强度提高了3.77倍.     

径向偏振光下的长焦、紧聚焦表面等离子体激元透镜

表面等离子体激元透镜(plasmonic lens, PL)是一种通过激发和操控表面等离子体激元 (SPPs), 突破衍射极限, 实现亚波长紧聚焦的纳米光子器件. 如何实现高效率的紧聚焦及调控, 一直是研究PL的重点. 如果选取电矢量沿径向振动的径向偏振光作为PL的入射光, 可从各个方向激发SPPs, 提高紧聚焦的能量效率. 本文提出了一种在径向偏振光激发下的长焦深、长焦距、亚波长紧聚焦的表面等离子体激元透镜, 该透镜由中心T 形微孔、阶梯形同心环和同心环结构组成. 本文首先利用有限元方法数值分析了中心微孔-同心环结构透镜的聚焦特性, 结果显示径向偏振光由底部入射可高效激发SPPs, 并且中心微孔透射光与散射至自由空间的SPPs由于多光束干涉形成了紧聚焦. 为进一步压缩焦斑、增加焦距、加深焦深、改善透镜聚焦特性, 本文引入中心T形微孔-阶梯形同心环结构, 从而对阶梯表面的SPPs同时提供了相位调制和传播方向的控制. 经过参数优化, 该透镜结构实现了光斑焦深、半高宽、焦距分别是入射光波长的2.5倍、0.388 倍、3.22倍的亚波长紧聚焦; 而且该透镜具有结构紧凑、尺寸小、易于集成的优点, 满足了纳米光子学对于器件微型化和高度集成化的要求. 该研究结果在纳米光子集成、近场光学成像与探测、纳米光刻等相关领域具有潜在的应用价值.     

亚波长金属波导的光传播和干涉特性研究

利用时域有限差分方法研究了亚波长金属波导TE波的传播特性和基于异常透射现象的干涉特性.对各种参量对驻波特性的影响及两列波导间的耦合特性进行了分析.研究发现,TE波在波导中传播时存在截止宽度,如果波导宽度小于截止宽度,TE波在波导中不能传播;如果波导宽度大于截止宽度,TE波的传播距离将随波导宽度变大而突然增加.当波导宽度达到或大于半波长时,TE波可以在波导中正常传播.金属波导的截止宽度与金属的吸收系数成正比.此外,由于光在亚波长金属波导透射时的异常透射现象,在亚波长金属波导中产生了TE波的干涉现象,能形成驻波.     

亚波长金属波导的光传播和干涉特性研究

利用时域有限差分方法研究了亚波长金属波导TE波的传播特性和基于异常透射现象的干涉特性.对各种参量对驻波特性的影响及两列波导间的耦合特性进行了分析.研究发现,TE波在波导中传播时存在截止宽度,如果波导宽度小于截止宽度,TE波在波导中不能传播;如果波导宽度大于截止宽度,TE波的传播距离将随波导宽度变大而突然增加.当波导宽度达到或大于半波长时,TE波可以在波导中正常传播.金属波导的截止宽度与金属的吸收系数成正比.此外,由于光在亚波长金属波导透射时的异常透射现象,在亚波长金属波导中产生了TE波的干涉现象,能形成驻波.     

双环角向偏振光束深聚焦特性

基于Richards-Wolf矢量衍射积分公式,研究了双环角向偏振光束经环状高数值孔径透镜的聚焦特性,推导了双环角向偏振光束经环状透镜深聚焦的光强表达式。根据数值模拟结果,比较了相关参量的变化对深聚焦特性的影响。研究表明:入射光束经环状高数值孔径透镜聚焦后,在焦平面得到了具有广泛应用的亚波长空心光斑,并且入射光束的相关参数和聚焦透镜的数值孔径大小都会影响光束的聚焦特性,使聚焦空心光斑达到亚波长量级;双环角向偏振光束经环状高数值孔径透镜的聚焦以后,在焦平面附近产生了一个更长的焦深（约28倍入射光波长）。     

基于一维金属光子晶体平凹镜的柱矢量光束亚波长聚焦

柱矢量光束具有柱对称性的偏振分布,其独特的光场分布和聚焦特性被广泛应用于光学微操纵及光学成像等领域,并迅速向亚波长尺度拓展.通常,亚波长尺度聚焦采用等离激元透镜实现,但存在光场调控的偏振态局限性.而借助光子晶体的负折射效应,不仅能够实现亚波长聚焦或成像,而且应对正交偏振态同时有效.采用对电磁波具有更强调控能力的一维金属光子晶体结构,计算得到的能带结构和等频曲线表明其负折射效应在特定波段对正交偏振态同时有效.在此基础上设计出一维金属光子晶体柱对称平凹镜结构,通过有限元算法模拟显示了可见光波段的径向和旋向偏振光的同时亚波长聚焦行为.进一步的结果表明,改变柱矢量光束的偏振组分能够直接有效地调节焦场空间分布及偏振分布特性.所提出的平凹镜结构能够实现对任意偏振组分的柱矢量光束的亚波长尺度聚焦,且该结构的设计对于各波段情况均有参考意义.该研究结果对小尺度粒子的光学微操纵、超分辨率成像等相关领域具有潜在的应用价值.     

介质填充型二次柱面等离激元透镜的亚波长聚焦

本文提出了一种亚波长聚焦的表面等离激元透镜,该透镜由二氧化硅填充金膜纳米狭缝阵列组成,金膜的出射表面为二次柱面.表面等离激元在狭缝入口处激发并沿狭缝传输,在狭缝出口转变为带有一定相位延迟的自由空间传播的光波.通过对透镜结构参数的控制,可以调节来自各狭缝的光波间的相对相位,使它们在设定的焦点处进行相长干涉,从而实现聚焦效果.本文用时域有限差分法数值计算了二次柱面等离激元透镜的聚焦特性.数值模拟结果表明,所设计的孔径为2μm的透镜,能够实现微米级焦距和焦深、且焦斑半高宽低至0.4倍波长的亚波长聚焦.该表面等离激元透镜结构简单紧凑、尺寸小,有利于光子器件的集成,在集成光学、光学微操纵、超分辩率成像、光存储、生化传感等相关领域有潜在的应用价值.     

金属-绝缘体-金属布喇格反射腔的窄带滤波研究

利用有限时域差分法模拟金属-绝缘体-金属布喇格反射腔的窄带滤波现象,发现在一维亚波长金属-绝缘体-金属波导的共振波长对应的电场振幅分布的波腹位置上打上直角型凹槽时,可以产生光子禁带和导带,本文主要研究其导带的成因及出现位置.其中光子导带对应的中心波长出现在共振波长附近;调节凹槽的几何结构,采用双重金属-绝缘体-金属布喇...     

Proposal and analysis of artificial dielectric lens with metallic corrugated structures for terahertz wave band

Optical devices for the terahertz wave band are being developed now and require better designs. This paper proposes an artificial dielectric lens with metallic corrugated structures for the terahertz wave band. A periodic analysis model extracted from the full model by assuming periodicity confirms the phase delay, which produces the focusing effect. Full model analysis also confirms the focusing effect. The full model analysis also confirms that the focusing length is longer as the spacing of corrugated baffles is wider. The focusing length is longer the metallic groove width is wider. The focusing length is longer as the groove depth is shallower. The lens shape without grooves does not produce the focusing effect. The results of the full model analysis are qualitatively consistent with those of the periodic model ones. This implies that the design for an exact size lens is possible by using the periodic model.     

Fresnel light modulator with an array of channel waveguides

One-dimensional focusing and optical modulation have been achieved using a Fresnel light modulator (FLM) based on a Fresnel lens consisting of Ti-diffused channel waveguides on LiNbO₃. By this device, the height of diffraction pattern near the focal point is modulated with an applied voltage while the focusing effect is almost kept. The experimental results obtained from the FLM with 13 zones at 633 nm are as follows: the focal length is 12.4 cm, the full width of beam at half power 47 μm, the half-wave voltage 28 V, the extinction ratio 10.9 dB and the insertion loss 11.6 dB.     

高斯激光驻波场沉积Na原子的量子理论分析

利用量子理论,通过CRANK-NICOLSON数值方法对23Na原子受激光驻波场作用的物理过程进行模拟.模拟结果表明:正失谐时,原子以λ/2为周期会聚在驻波光场中波节处.随着光势阱加深或原子纵向速度改变,原子会聚结果分别符合薄透镜、厚透镜及沟道化模型.厚透镜模型中,当原子纵向速度增加,原子密度峰位置沿z方向向后漂移,峰在z方向半高宽增加.当激光功率增加或激光束腰减小,会聚面上峰半高宽减小,对比度增加,峰值增加.     

Generation and tight-focusing properties of cylindrical vector circular Airy beams

Tight-focusing properties of cylindrical vector circular Airy beams [i.e., azimuthally polarized (AP) circular Airy beam and radially polarized (RP) circular Airy beam] passing through a high numerical aperture thin lens are investigated in detail. It is found that a super long subwavelength dark channel with full width at half maximum about 0.49λ and depth of focus (DOF) about 52λ can be achieved near the focal region for the case of tight focusing of an AP circular Airy beam, and a super long needle with DOF about 27.5λ of strong longitudinally polarized field can be obtained near the focal region for the case of tight focusing of a RP circular Airy beam. Furthermore, we report experimental generation of an AP circular Airy. Our results will be useful for atom guiding and trapping, particle acceleration and fluorescent imaging.     

表面等离子体平面金属透镜及其应用

由于衍射极限的存在,传统光学透镜成像分辨率理论上只能达到入射光波长的一半。通过恢复和增强携带物体细部特征信息的高频倏逝波,基于表面等离子体的平面金属透镜有望突破这种光学衍射极限,实现超分辨成像。本文对平面薄膜式与纳米结构式两类平面金属透镜进行了综述,详细介绍了若干典型平面金属透镜的结构设计、工作机理及其聚焦性能,并对其特点与存在的问题进行了分析与讨论。由于光波在金属中传播时存在一定损耗,如何更高效地增强高频倏逝波信号并转换成传播波,使其参与成像,以更好地实现远场超分辨成像,以及如何进一步增大近场超高分辨率聚焦光斑焦深以及减小远场聚焦光斑尺寸,是表面等离子体平面金属透镜进一步研究的重点。     

Determination of the focusing power of flat lenses using the radiovisor

Focusing of electromagnetic radiation of a point source with a wavelength of 3 cm by flat negative-refraction lenses formed by a hexagonal structure of metal cylindrical rods was studied. The spatial distribution of microwave field of H polarization in the lens focal plane was recorded by a radiovisor screen which converts it into a visible image. The full width at half maximum of the focal spot distribution at optimum focusing did not exceed half the emission wavelength.     

Focus depth characteristics of lenses with long focal depth designed by a focal depth function

The validity of a focal length function is investigated in designing optical element with long focal depth and high lateral resolution. The designed lenses with different starting focal length are studied. Two focusing performance measures, focal depth and lateral resolution, are presented. Comparing with the conventional lens and optical element designed by other focal length function, numerical results of the designed optics element indicate that the long focal depth and high lateral resolution are achieved. The validity of the focal length function is confirmed. Meanwhile, the designed optical element is similar with the lens with spherical aberration. It means that one can easily implement long focal depth by applying appropriate phase modulation to a lens with spherical aberration.     

Generation of multiple focal holes by tightly focused azimuthally polarized double-ring-shaped beam with complex phase mask

We study the focusing properties of a tight focusing of double ring shaped azimuthally polarized beam through complex phase mask (CPM) with high NA objective lens, based on vector diffraction theory. A novel design to generate an azimuthally polarized subwavelength focal hole having FWHM of 0.332λ with long focal depth of about 18.8λ is illustrated numerically. Apart from generating focal hole with long focal depth, it is observed that a properly designed CPM also generates multiple focal hole segments useful for laser cutting, microscopy and the manipulation of optical traps of low refractive index particles.     

Dual focus diffractive optical element with extended depth of focus

A dual focus property and an extended depth of focus were verified by a new type of diffractive lens displaying on liquid crystal on silicon (LCoS) devices. This type of lens is useful to read information on multilayer optical discs and tilted discs. The radial undulation of the phase groove on the diffractive lens gave the dual focus nature. The focal extension was performed by combining the dual focus lens with the axilens that was invented for expanding the depth of focus. The number of undulations did not affect the intensity along the optical axis but the central spot of the diffraction pattern.     

Generation of sub wavelength focal spot with large depth of focus generated by radially polarized beam

We investigate the focusing properties of a radially polarized Bessel Gaussian beam by a high numerical aperture (NA) lens based on vector diffraction theory. We observe that our proposed system generates a sub wavelength focal spot of 0.42λ having large uniform focal depth of 6.45λ. The authors expect such a long depth of focus have great potential for use in optical, biological, high-resolution and atmospheric sciences.