亚波长抗反射光栅结构的设计及制备

针对现有亚波长抗反射光栅结构参数对加工工艺要求较高且难以制备等问题,设计了一种方柱形二维抗反射光栅结构。依据等效介质理论和薄膜增透理论对亚波长抗反射光栅结构参数进行仿真分析,结果表明其透射率在远红外波段20～24 μm平均透射率能够达到98%,中心波段21.8 μm处透射率达到99%。使用飞秒激光直写方式进行实验制备,测得平均透射率达77%,中心波段透射率达到77%,与仿真结果相近。经实验验证,所设计的亚波长光栅结构的工艺容差较现有光栅结构更好,且对实验加工精度要求较低,为其他类似光栅结构的设计和加工提供了新的思路。     

基于亚波长二维光栅的入射角不敏感颜色滤光片研究

提出了一种基于二维亚波长光栅的具有非偏振光入射下入射角不敏感特性的反射式颜色滤光片. 采用严格耦合波分析方法详细分析了光栅周期、光栅层厚度以及固定光栅占空比下光栅的结构尺寸对反射率峰值、反射带位置及带宽的影响. 结合入射角不敏感特性, 经过优化设计得到了光栅的最终结构参数, 获得了中心波长424 nm, 峰值反射率56%, 带宽45 nm的反射滤光片.模拟结果表明, 在非偏振光入射下, 此滤光片的反射光谱表现出显著的入射角不敏感特性. 当入射角高达60°时反射带的中心波长偏移6 nm 反射率下降6%带宽增加8 nm 其参数没有较大变化通过调整光栅的结构参数可在400–520 nm范围内调节滤光片的中心波长以获得不同颜色的入射角不敏感滤光片. 关键词： 反射式滤光片 二维亚波长光栅 入射角不敏感 严格耦合波分析     

基于Bragg反射面结构的衍射光栅设计与研究

基于Bragg反射光栅是一维光子晶体的一种特例结构,本文提出利用一维光子晶体带隙理论进行Bragg反射光栅设计.通过光学仿真软件OptiFDTD对Bragg反射光栅的宽度及倾斜角度误差的仿真分析,发现Bragg光栅齿刻槽宽度变化在10%范围、倾斜角度10°以内不会引起Bragg光栅衍射效率的明显变化,说明Bragg反射光栅具有较高的工艺误差容限;根据一维光子晶体带隙理论,设计了一种罗兰圆结构的Bragg衍射双光栅结构模型,实现了两个频段之间的衍射分光,优化分析结果表明:当第一套光栅中Bragg周期层数为6、第二套光栅Bragg周期层数为10时,两频段波长的衍射效率均可以达到70%左右,明显高于传统深刻蚀的衍射光栅.基于本设计的波分复用器是一种尺寸小、衍射效率高的新型EDG波分复用器,为未来高效密集型EDG波分复用器发展提供了一种新的设计思路.     

基于共振异常的消偏振型窄带滤波器分析

亚波长光栅因光栅参量的不同而具有不同的衍射特性,通过对亚波长光栅参量的合理设计来实现消偏振窄带滤波是一种新的方法与途径。首先分析了基于共振异常的窄带滤波的物理机制及存在条件,讨论了二维亚波长光栅实现消偏振窄带滤波的可能性。然后,利用严格模式理论进行了计算模拟,其计算结果与导波理论所得结果基本吻合,其衍射特性表现出周期性共振异常、敏感的角度依赖性和波长依赖性。最后,讨论了由工艺误差对滤波特性所带来的影响。为具体工艺制作提供了一定的指导。     

基于叠栅技术的二维亚波长周期结构成像设计

用光子学方法研究了叠栅技术中,当试件光栅被拉压和旋转后,叠栅条纹的空间周期和相对于基准光栅的取向,试件光栅被拉压后的节距等相关问题。根据衍射光波的空间周期可能大于试件光栅空间周期的特点,对二维亚波长周期结构衍射成像进行了设计研究。首先,对二维亚波长周期结构衍射物进行编码,以获得包含编码光栅空间信息的均匀波;其次,使编码得到的均匀波通过光学系统,并被放大到CCD相机所能辨识的大小;再次,经解码光栅解码,滤掉编码波,最终获得二维亚波长周期结构物的空间结构信息,达到超分辨的目的。同时,对成像过程进行了较为详尽的分析,对编码器、解码器的位置以及它们相对衍射物的取向进行了设计研究,对滤波器的选择给予了必要的说明,指出了取得超分辨成像的关键。     

一种新型的光纤光栅调Q掺Er光纤激光器

报道一种采用光纤光栅迈克尔逊干涉仪结构实现掺Ｅｒ光纤Ｑ－开关激光输出的实验，其中的全光纤迈克尔逊干涉仪由二个相同的光纤光栅构成，用来作为激光腔的其中一个反射镜，它同时提供了对激光输出波长的造反作对腔面反射率进行调制的二个功能，实验得到稳定的激光输出波长在１５４５．７０μｍ，脉冲功率为５００ｍＷ，脉宽为１．３μｓ，重复频率为１７ｋＨｚ。     

一种提高OLED基底出光效率的亚波长光栅设计

为了提高OLED出光效率,在OLED基底表面设计了二维连续表面亚波长光栅。利用等高台阶逼近的方法近似连续表面光栅结构,并结合等效介质理论和薄膜光学原理,设计光栅参数:刻蚀深度0.29 μm,周期大小0.165 μm,底边直径与周期的比值等于1,可以实现宽光谱、广角度的高透射率。利用时域有限差分方法仿真计算了该光栅对OLED基底出光效率的影响,结果表明,出光效率最高可提高30%。     

Ge0.05Si0.95/Si异质结单模共面布拉格反射波导光栅的设计与分析

GeSi/Si异质结布拉格反射光栅是硅基光电集成领域一种重要的集成光学器件,分析GeSi/Si异质结的传光特性和布拉格条件,通过求解布拉格光栅方程,得出耦合系数和耦合效率。利用上述原理设计出入射角为66°,波导层的厚度为2μm,光栅长度为4252μm,槽深为0.05μm,光栅周期为0.456μm,滤波带宽为0.214nm,耦合效率为84.1%的1.3μm Ge_0.05Si_0.95/Si异质结单模共面布拉格反射光栅,并用数值模拟了入射光波电场和反射光波电场的分布。     

新型弯曲不敏感光纤中写入的长周期光纤光栅

报道了一种用高频CO2激光器在有纳米环结构的新型弯曲不敏感光纤上写入的长周期光纤光栅。实验表明只有周期在两个特定的范围内的长周期光纤光栅在1200-1650nm波长范围内会有明显的谐振峰出现。对两个周期分别为295μm和470μm的长周期光纤光栅的温度和应变特性进行了研究。实验结果显示周期为295μm的长周期光纤光栅的...     

两种亚波长金属波片的透射特性对比

综合等效介质理论和表面等离子激元(SPP)Bloch模型,对比分析了两种新的亚波长光栅结构:二维矩形金属光栅和二维椭圆柱金属光栅。利用时域有限差分(FDTD)算法,对比分析了两种结构的透射率及其相位延迟与入射光波长及偏振角变化的关系,尤其两种结构实现λ/4波片功能所对应的透射特性。仿真结果表明,当入射光偏振角为75°时,两种结构均可实现λ/4波片功能,此时二维矩形和椭圆柱金属光栅的透射率分别为0.77和0.67,表明二维矩形金属光栅比椭圆柱光栅具有更好的透射效果。对应550～800nm的入射波长,两种光栅在各自允许的入射偏振角范围内均表现了较为平坦的宽带透射特性。     

Subwavelength structures for high power laser antireflection application on fused silica by one-step reactive ion etching

In this paper we report a simple method to fabricate a novel subwavelength structure surface on fused silica substrate using one-step reactive ion etching with two-dimensional polystyrene colloidal crystals as masks. The etching process and the morphologies of the obtained structure are controlled. We show that the period of the obtained fused silica pillar-like arrays were determined by the initial polystyrene nanoparticle size. The height of pillar arrays can be adjusted by controlling the etching duration, which is proved to be of importance in tailoring the antireflection properties of subwavelength structures surface. The novel subwavelength structures surface exhibit excellent broadband antireflection properties, but the size of the pillar affects the antireflective properties in short wavelength region. We anticipate this method would offer a convenient and scalable way for inexpensive and high-efficiency high power laser field designs.     

Investigation of geometrical effects of antireflective subwavelength grating structures for optical device applications

We calculated diffraction efficiencies of subwavelength grating (SWG) structures for various optical device applications by using a rigorous coupled-wave analysis method. The geometrical effects, such as grating shape, height, and period, were investigated in order to obtain better antireflection performance. Cone shaped SWG structures with a taller height provide lower reflectance over a broadband wavelength range compared to that of flat surface and nanorod. It was found that the low reflection regions are quite related with the grating period and the refractive index of substrate materials. From the comparison between external and internal reflection of SWG structures, we also showed that the internal reflection requires shorter grating period than the case of external reflection to acquire broadband antireflection properties.     

Colloidal subwavelength nanostructures for antireflection optical coatings

A two-dimensional (2D) subwavelength nanostructure for antireflection coating is fabricated upon a transparent substrate. Self-assembled 2D colloidal crystals are used as a nanoscale composite material with controlled thickness and low refractive index. The feature size of the structure is approximately 105 nm. The structure is used for antireflection coating, and the measured reflectivity of a glass substrate is reduced to 0.3%. Enhanced transmission through the substrate is also observed.     

Diffraction grating with rectangular grooves exceeding 80% diffraction efficiency

A novel design for a surface relief grating with rectangular grooves is presented. The first reflected diffraction order shows experimentally 84% diffraction efficiency for a metallic grating. The required binary surface relief can be manufactured by using one single microlithographic fabrication step similar to standard processes in microelectronics. Each period of the grating consists of a subwavelength “minilattice” with a variable duty cycle. A theoretical model of the structure is presented and compared to measurements at 10.6 μm wavelength. Applications ranging from deflectors, polarizing beam splitters, variable attenuators to general diffractive components such as kinoforms for laser beam shaping are proposed.     

基于超材料的中波红外宽带偏振转换研究

基于硅纳米块阵列和亚波长金属光栅,硅纳米块长轴与金属光栅夹角为45°,本文设计了一种高效、宽带偏振转换结构.模拟计算表明该结构实现了线偏振光90°旋转,在3.4—4.5μm波段偏振转换率大于60%,在3—5μm光谱范围内的转换对比率大于10~4.由于该结构光学性能优异,制备难度低,可以应用于光传输控制.     

一种设计环形汇聚光栅反射镜的新方法

提出了一种利用数学变换来快速设计环形汇聚光栅反射镜的方法.通过分析具体的物理场景,抽象出已有条形汇聚光栅的"线"汇聚特性与所要设计的"点"汇聚特性在数学上对应的变换关系,然后用该数学变换对条形汇聚光栅进行外形上的变换,外形变换后的条形光栅即为可以实现"点"汇聚的环形光栅.用有限元算法对设计的环形汇聚光栅进行仿真,仿真证明采用该方法设计的环形光栅可以很好地实现高反、高汇聚.采用这一方法,设计了直径为29.788μm的环形光栅反射镜,当垂直入射的径向偏振光从设计的环形光栅表面反射回来后将发生汇聚,汇聚焦点位于环形光栅表面10μm处.经计算,反射镜的数值孔径为0.8302,反射率为0.9163,在焦点所在的汇聚面上,汇聚光栅电场分布的半高宽为1.5548μm.     

锥形轮廓亚波长二维表面浮雕结构的矢量衍射特性

本文利用严格耦合波理论对多台阶逼近锥形轮廓的亚波长二维表面浮雕结构进行了计算分析.从本文的计算结果来看,采用多台阶来逐步逼近锥形轮廓的亚波长零级二维表面浮雕结构具有在宽波段、大视角上能够实现抗反射,并且对光波的偏振态下不敏感的特性.从而使得该结构为薄膜光学在材料的选择方面提供了极大的选择自由度.     

Area-coded effective medium structures, a new type of grating design

We propose a new way to design gratings with desired diffraction properties by using subwavelength feature sizes perpendicular to the ordinary superwavelength grating period. This is different from well-known one-dimensional binary-blazed gratings that use a structuring along the grating period and thus opens new flexibility in generating arbitrary effective-index distributions in the direction of the grating period. Since the subwavelength features form contiguous areas, they are called area-coded effective medium structures (ACES). Compared with well-known binary subwavelength structures in two-dimensional arrangements consisting of pillars, ACES are more stable and have comparable efficiency properties. As an example we show how to design in principle a four-level area-coded effective medium grating, compare the efficiency of ACES with binary-blazed and échelette gratings, and optimize the subwavelength period of ACES.