A mixed metal dielectric sandwiched grating for polarization-selective reflection

A mixed metal dielectric sandwiched grating is described for polarization-selective reflection. The novel grating is composed of substrate, metal slab, two dielectric grating layers, and covering layer. The polarization-selective grating is optimized by using rigorous coupled-wave analysis for the usual duty cycle of 0.5. With the optimized grating parameters, reflective efficiency of 96.49% can be diffracted into the −1st order for TE polarization. And two-port output of 48.26%/48.27% can be diffracted into the 0th and the −1st orders for TM polarization. Polarization-selective reflection with good performance can be obtained by the mixed metal dielectric sandwiched grating. The usual duty cycle of 0.5 makes it easy and simple to be fabricated for practical applications. Moreover, the polarization-selective beam splitter based on the mixed metal dielectric sandwiched grating has advantages of wide incident wavelength range for TE polarization and angular bandwidth for TM polarization.     

A reflective surface-relief two-layer grating for splitting beams with the polarization-selective property

A polarization-selective beam splitter is presented based on a reflective surface-relief two-layer grating with a metal slab. The grating is composed of two dielectric layers and a metal slab on the substrate. For TE polarization, efficiencies of 97.58% can be diffracted into the reflective −1st order. For TM polarization, two-port output of 47.55% and 47.11% can be split into the 0th order and the −1st order, respectively. Such a polarization-selective beam splitter can be fulfilled by one grating in reflection. The grating depths of two layers are optimized by using rigorous coupled-wave analysis with the given duty cycle of 0.6 and period of 1100 nm. The performance for different incident conditions is investigated when the incident wavelength and angle deviate from the central wavelength and the Bragg angle, respectively. For TM polarization, good uniformity can still be achieved within the given incident wavelength and angle regions. For TE polarization, the reflective polarization-selective beam splitter can have merits of wideband for different incident wavelengths.     

Connecting-layer-based polarizing beam splitter grating with high efficiency for both TE and TM polarizations

We describe a novel polarizing beam splitter (PBS) of transmission connecting-layer-based grating, which can show high efficiency for TE polarization in the ?1st order and TM polarization in the 0th order. According to the modal method, grating duty cycle and period are prescribed to obtain high efficiency for TM polarization. Using the rigorous coupled-wave analysis, grating depth and thickness of the connecting layer are optimized to achieve high efficiency for TE polarization. The presented PBS has advantages of wideband properties for incident wavelength and angle. Most importantly, the efficiency is improved greatly for TE polarization compared with the reported PBS based on fused-silica grating.     

Theoretical reflective performance of a sandwiched two-layer grating polarizer

The reflective polarizer is described by a sandwiched two-layer grating with a metal slab. Such a new polarizer is aimed to improve the performance of a reflective grating-based polarizer. The grating is optimized with the usual duty cycle of 0.5, where TE and TM polarizations are reflected in the –1st and the 0th diffraction orders, respectively. With optimized grating parameters, the extinction ratio can reach 45.5 dB and 41.9 dB in two diffraction orders, which are greatly improved compared with the conventional reported surface grating polarizer with the simple structure. Attractive merits of the new design are high efficiency, high extinction ratio, wide incident wavelength bandwidth for TE polarization, and wide angular range for TM polarization. Numerical results are expected to open new opportunities for the design of a grating-based polarizer with the enhanced performance by the complicated grating configuration.     

共振域矩形介质光栅的逆向设计

采用模态法研究了共振域光栅分束器及闪耀光栅等光学器件的设计原理及逆向设计方法,给出了-1级非偏振闪耀光栅的典型设计示例。研究表明,自准直角入射时,光束在光栅内传输将激发产生离散模,通过调节离散模透过光栅传输时的累积相位差,可对衍射光进行调控,实现偏振(非偏振)分束、偏振(非偏振)闪耀等功能。采用严格耦合波法对基于模态法逆向设计的-1级非偏振石英闪耀光栅的几何参数进行验证,计算结果显示两者非常吻合,证明了该方法的正确性。     

Polarizing beam splitter of a deep-etched fused-silica grating

We described a highly efficient polarizing beam splitter (PBS) of a deep-etched binary-phase fused-silica grating, where TE- and TM-polarized waves are mainly diffracted in the -1st and 0th orders, respectively. To achieve a high extinction ratio and diffraction efficiency, the grating depth and period are optimized by using rigorous coupled-wave analysis, which can be well explained based on the modal method with effective indices of the modes for TE/TM polarization. Holographic recording technology and inductively coupled plasma etching are employed to fabricate the fused-silica PBS grating. Experimental results of diffraction efficiencies approaching 80% for a TE-polarized wave in the -1st order and more than 85% for a TM-polarized wave in the 0th order were obtained at a wavelength of 1550 nm. Because of its compact structure and simple fabrication process, which is suitable for mass reproduction, a deep-etched fused-silica grating as a PBS should be a useful device for practical applications.     

Design of a 50/50 splitting ratio non-polarizing beam splitter based on the modal method with fused-silica transmission gratings

The optical design of a beam splitter that has a 50/50 splitting ratio regardless of the polarization is presented. The non-polarizing beam splitter (NPBS) is based on the fused-silica rectangular transmission gratings with high intensity tolerance. The modal method has been used to estimate the effective index of the modes excited in the grating region for TE and TM polarizations. If a phase difference equals an odd multiples of π/2 for the first two modes (i.e. modes 0 and 1), the incident light will be diffracted into the 0 and ?1 orders with about 50% and 50% diffraction efficiency for TM and TE polarizations, respectively.     

基于亚波长光栅的VCSEL偏振控制研究

为了确定亚波长光栅在微电机械系统(MEMS)波长可调谐VCSEL不同位置(上DBR上表面、上DBR下表面以及内腔)中实现TE和TM偏振控制的光栅参数范围以及光栅在哪个位置时实现偏振控制最稳定,通过MATLAB建立MEMS波长可调VCSEL的模型,然后计算光栅在3种位置时上反射镜(包括空气隙和光栅)随光栅参数变化的反射率,以此来确定它们实现TE/TM稳定偏振的光栅参数范围(即高反射范围内的参数)。将各自的高反射所对应反射率减去相同光栅参数范围内TM/TE低反射对应的反射率,通过反射率差值确定光栅在哪种位置时MEMS波长可调谐VCSEL实现偏振是最稳定的。最后得出的结论是光栅在上DBR下表面几乎无法控制TM偏振,而将光栅放置于内腔中,无论是在TE偏振控制上还是TM偏振上都是最稳定的。在实现TE偏振稳定的参数范围内,TE的阈值增益比TM最小少10 cm~(-1);而在实现TM偏振稳定时,在TE偏振稳定的参数范围内,TE的阈值增益比TM最小少5 cm~(-1)。     

Polarizing beam splitter of deep-etched triangular-groove fused-silica gratings

We investigated the use of a deep-etched fused-silica grating with triangular-shaped grooves as a highly efficient polarizing beam splitter (PBS). A triangular-groove PBS grating is designed at a wavelength of 1550 nm to be used in optical communication. When it is illuminated in Littrow mounting, the transmitted TE- and TM-polarized waves are mainly diffracted in the minus-first and zeroth orders, respectively. The design condition is based on the average differences of the grating mode indices, which is verified by using rigorous coupled-wave analysis. The designed PBS grating is highly efficient over the C+L band range for both TE and TM polarizations (>97.68%). It is shown that such a triangular-groove PBS grating can exhibit a higher diffraction efficiency, a larger extinction ratio, and less reflection loss than the binary-phase fused-silica PBS grating.     

Design of wire-grid polarizer with effective medium theory

A design concept of a wire-grid polarizer, which is based on the effective-medium theory, has been proposed. The effective indices of a wire-grid grating are evaluated with the effective-medium theory. The results show that, the wire-grid grating acts as a metal for TE polarization, but it behaves like a dielectric material for TM polarization. According to the different effective optical properties of the wire-grid grating for the different polarizations, a wire-grid polarizer with a high polarization ratio can be obtained by enhancing both the transmission for TM polarization and the reflection for TE polarization.     

Polarization-selective subwavelength grating used with 193 nm light

Hyper-NA ArF (193 nm) immersion lithography is one of the most potential technologies to achieve 32 nm critical dimension node. At the corresponding large angles in the photoresist, control of polarization becomes necessary. A polarization beam splitter (PBS) based on a subwavelength dielectric grating has been designed for use with 193 nm light. The polarization-selective property of such grating is explained by the mechanism of mode interference. The designed grating working as a 1 × 2 beam splitter can transmit TM wave (∼ 90%) to the zeroth order with extinction ratio of 753, and it diffracts TE wave (∼ 80%) to the −1st order with extinction ratio of 300.     

A detailed study of metallic surface-relief grating

This paper presents a more detailed interaction of an electromagnetics light with a metallic surface-relief subwavelength grating utilizing the rigorous coupled-wave analysis. The focus of this work is the accurate modeling of undetermined aspects of diffraction patterns produced by binary metallic grating structures, specially gold grating. First-order diffraction efficiency for rectangular-groove gold grating with equal groove and ridge widths are presented for various wavelengths as a function of period, groove depth, polarization and angle of incidence. We also studied diffraction efficiency of both of TE and TM polarization modes against increasing of incident angle as well as TE polarization against increment of grating period. As a result, very low reflectivity at zero-order was found out for TE and TM polarizations at the pitch of Λ = 2λ. Having been studied diffraction efficiency of metallic surface-relief gratings, we also examined polarization-dependent efficiency of diffraction orders, for different groove depths. Simulation results have been completely presented.     

红外波段高效率低偏振相关损耗光栅的设计

衍射效率高、偏振相关损耗低的衍射光栅是集成波分复用/解复用器件的一种核心元件,在光通信中具有很重要的应用价值。通过利用严格的耦合波理论计算光栅衍射效率的方法,分别编制出了计算TE波和TM波的衍射效率程序。通过改变光栅的面形来进行计算,最终得到了衍射效率高和偏振相关损耗小的光栅面形。     

Metal-mirror-based grating for high-efficiency element in dense wavelength division multiplexing

It is desirable to obtain high efficiency with polarization-independence and wideband properties for incident wavelength. A metal-mirror-based grating is presented to diffract the incident wave into reflection orders with high efficiency for TE and TM polarization. The modal method and rigorous coupled-wave analysis (RCWA) are used together to optimize a metal-mirror-based grating effectively. From the analysis of the modal method, it is feasible to realize such a grating with the prescribed grating duty cycle and period. Accurate parameters of the grating depth and thickness of the connecting layer are optimized using RCWA. Compared with the reported binary simple grating, high efficiency can be improved greatly for the incident wavelength of 1550 nm in dense wavelength division multiplexing. The diffraction investigation indicates that a wideband property for incident wavelength can be obtained for such a novel metal-mirror-based grating.     

Complete Polarization Conversion Characteristics of Dielectric Grating Composed of Left-Handed Materials

The TE/TM polarization conversion characteristics of dielectric grating composed of left-handed materials for the case of plane wave oblique incidence are carefully investigated by a method which combines the multimode network theory with the rigorous mode matching method. It is indicated that complete polarization conversion between TE and TM modes can be realized using left-handed gratings. This can hardly achieve in the conventional right-handed gratings. Comparisons of polarization conversion properties between right-handed gratings and left-handed gratings are given with physical explanations. This unique merit of left-handed periodic structure is of important significance for accurate design of new millimeter wave TE/TM polarization converters.     

Bragg反射齿型平面凹面衍射光栅性能研究

本文基于Bragg反射光栅是一维光子晶体的一种特例结构, 提出利用一维光子晶体理论进行Bragg衍射光栅的设计并对其性能进行研究分析. 根据一维光子晶体理论, 建立了罗兰圆结构的凹面椭圆Bragg蚀刻衍射光栅, 研究了TE/TM模式下器件的分光特性以及入射角度改变对器件角色散造成的影响; 同时, 文中对比了空气介质型和金属铝线型椭圆Bragg蚀刻衍射光栅的光学性能. 研究结果表明: 选择合适的器件参数, 可以实现TE/TM模式下1.465-1.615 μm范围内波长衍射效率在95% 以上, 且空气介质型结构光栅的通道均匀性要优于金属铝线型结构光栅; 入射角在30°-60°范围内变化时, 相同入射角度下, TM模式下器件角色散大于TE模式. 基于Bragg衍射光栅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, 为未来密集型EDG波分复用器发展提供了一种新的设计思路.     

一维增透亚波长光栅的研究

将具有高透射性的亚波长光栅置于微机械波长可调谐垂直腔面发射激光器(VCSEL)的内腔当中可以提高波长的调谐范围,为了使波长调谐范围达到最优则必须优化高透射性的亚波长光栅使其透射率达到最大。利用严格耦合波法分析了亚波长光栅的占空比、周期、厚度和入射角对其透射率的影响并找出最优的光栅参数。通过计算分析可得,对于TE和TM偏振存在最佳的占空比使其透射率达到99.5%。在文中条件下,它们对应的占空比分别为0.23和0.80。而光栅厚度对于TE和TM偏振透射率的影响是周期性的,在一个周期内存在一个最佳值使其透射率达到最高。在文中条件下,TE偏振的厚度周期是150 nm,TM偏振的厚度周期是300 nm。当光栅参数不变时,无论是TE还是TM偏振光,它们的透射率只有在垂直入射光栅时(入射角为0°)才能达到最大。而通过等效介质原理可以得出,周期对透射率没有影响。最后计算了透射率在光栅厚度和占空比同时变化时的变化趋势,并从中得出最优的光栅参数。     

Polarizing beam splitter of two-layer dielectric rectangular transmission gratings in Littrow mounting

We theoretically investigated the design of polarizing beam splitters (PBS) of two-layer dielectric rectangular transmission gratings in Littrow mounting. The PBS grating is aimed to separate TE and TM polarized waves into two different transmitted orders, i.e. the 0th and −1st orders. The polarization-dependent diffraction process is analyzed by using a simplified modal method. The mode reflection and transmission at the interface of the two layers are illustrated. Design equations are given based on the average mode indices of the even and odd modes inside the grating region, which are verified by using rigorous coupled wave analysis. Moreover, with simulated annealing algorithm, two kinds of two-layer PBS gratings are optimized for operation over the C-band (1520-1570 nm). Compared with the single-layer transmission PBS gratings, such two-layer scheme exhibits a great flexibility of design. The PBSs of two-layer dielectric transmission gratings should be useful for practical applications.     

埋入式光栅双通道特性及其应用研究

利用严格耦合波理论分析了埋入式光栅在45°入射时,垂直和平行于光栅栅线的两个不同观察平面的零级共振反射衍射特性.在垂直于光栅栅线的平面内,TE、TM偏振下零级反射共振波长分别为432 am和420 am,在平行于光栅栅线的平面内,TE、TM偏振下零级反射共振主峰波长分别为623 nm和620 nm,在两个平面内,零级共振衍射光的共振波长差别较大,观察到的衍射光颜色差别明显,定义为双通道特性并用实验进行证明,制作了相应的光变色器件.     

亚波长金属偏振分束光栅设计分析

结合有效介质理论和薄膜光学的抗反射设计方法,设计了基于0.65μm工作波长的亚波长金属偏振分束光栅,给出了光栅的优化设计参数,采用严格耦合波理论分析了光栅的偏振分束特性.结果表明,亚波长金属光栅对TE偏振表现为金属膜特性,具有高反射,对TM偏振表现为介质膜特性,具有高透射,在-30°<θ<30°的大入射角范围和0.47μm<λ<0.80μm的宽入射波谱内,该光栅的透射光和反射光均具有高偏振消光比和低插入损耗的特点. 关键词： 亚波长金属偏振分束光栅 有效介质理论 薄膜光学 严格耦合波理论