近红外亚波长硅光栅偏振器的设计

利用泄漏模共振效应以及等效介质理论设计出工作在近红外波段的一维亚波长硅光栅偏振器。采用散射矩阵方法和时域有限差分方法对结构进行设计和优化,模拟结果显示在正入射条件下,该偏振器在1284-1575nm波长范围内的消光比大于100（20dB）,而TM模的透射率高于98％。同时对该偏振器的角度特性以及制备容差进行了讨论,计算结果表明该偏振器具有较大的角度与制备容差。     

基于亚波长光栅的高集成度垂直光耦合器

设计了一种基于亚波长光栅的具有高集成度、高耦合效率的垂直光耦合器,在1.5～1.6μm波长范围内实现了大于97%的耦合效率,且器件长度仅为15μm,是传统基于绝热拉锥波导的垂直耦合器尺寸的十分之一,提高了系统的集成度。在亚波长光栅占空比、拉锥波导尖端尺寸以及波导错位方面,所设计的耦合器均具有较大的工艺误差容限,在异质集成领域展现出了良好的应用前景。     

亚波长金属线栅的设计、制备及偏振成像实验研究

针对红外偏振成像系统,运用等效介质理论,在氟化钙基底上设计了周期为200 nm,深度为100 nm的金属铝栅.模拟计算结果表明,设计的金属铝栅在中红外(3—5 μm)和远红外(8—12 μm)双波段范围内,以及±20°的视场范围内能够提供大于35dB的消光比.利用电子束曝光、反应离子束刻蚀、等离子去胶等工艺完成了金属铝栅的制作.将金属铝栅放在中波红外热像仪前,得到了目标轮廓清晰的偏振图像. 关键词： 亚波长衍射光栅 偏振成像 等效介质理论     

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。     

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     

亚波长消反射光栅

为了降低消反射光栅的偏振敏感性，将等效介质理论推广到二维亚波长结构，对一种特定的矩形柱状结构进行了分析。构造了一种分析方法，然后利用光栅结构的有关表达式得到这种二维结构的近似等效系数。并设计了适用于10．6μm红外波段的二维亚波长消反射光栅，用二元光学的制作工艺在si衬底上进行了实验制备。测试结果表明：对中心波长为10．6μm的红外光，这种光栅象单层消反射膜一样，具有很好的增透效果。     

一种条形亚波长径向偏振光栅

提出并设计了一种条形亚波长铝金属径向偏振光栅,用电子束直写方法制成,可以将偏振光偏振面的旋转直接转换为光斑的水平移动,通过定位光斑位移实现旋光角的测量.光栅由12000个单元水平排列组成,每个单元宽1μm,中心单元的格栅方向为0°,左右相邻单元的格栅分别按逆时针和顺时针方向依次旋转30″,最终实现±50°旋光角的测量范围.基于琼斯矩阵建立了光栅的理论模型,并运用严格耦合波理论分析了光栅的偏振特性与光栅脊厚、周期、占空比、入射光波长之间的关系,确定了光栅的最优结构.实验与仿真结果表明,光栅TM波的透过率大于80%、整体消光比大于26dB.这一测量模式不受光功率波动的影响,可以构成无机械旋转的新型旋光仪,或不需要旋转图像平移转换的电力光学传感器.     

亚波长光栅衍射效率特性设计的遗传算法优化

亚波长光栅中的衍射需要使用矢量衍射理论进行分析,其衍射效率与多个因素有关,对任意面形、任意入射条件的亚波长光栅的衍射来说,使用严格的耦合波理论进行分析计算可以得到数值解。通过分析不同参数条件下的衍射特性和衍射效率对各个参数的敏感性,获得了对衍射效率影响最大的光栅参数——槽深。用接近衍射效率曲线的抛物线作为目标函数建立了适应度函数。使用遗传算法进行优化,得到了所期望的衍射效率滤波特性,从而完成了具有防伪功能的亚波长光栅的设计。     

用于谐波分离的三角形槽亚波长光栅设计

根据亚波长光栅的导模共振异常特性,提出三角形槽亚波长光栅实现惯性约束聚变驱动器谐波分离的技术方案.定义了用于描述谐波分离性能优劣的谐波分离品质函数,对影响三角形槽亚波长光栅的谐波分离品质函数的光栅参量进行了详细的分析,基于矢量衍射理论设计了能够实现谐波分离的三角形槽亚波长光栅,确定了用于谐波分离的三角形槽亚波长光栅的设计思路和方法.     

面形误差对亚波长金属光栅偏振器性能的影响

基于严格耦合波理论分析了光栅面形误差对亚波长金属光栅偏振器偏振性能的影响.通过对数值结果的分析发现,光栅圆角误差、光栅侧壁倾斜误差和光栅表面粗糙误差对光栅的TM透射效率影响不大,但它们使得光栅的消光比明显降低.因此,面形误差使得光栅的偏振性能明显降低.理论分析表明,顶角为直角、侧壁垂直和表面光滑的理想矩形光栅结构的偏振性能最好.     

High resolution photolithography with sub-wavelength grating

Large area linear and crossed grating structures on steel surfaces are obtained by UV-femtosecond-laser ablation at 248 nm. High resolution on large areas is secured using a beam delivery system based on a two-grating interferometer. Thus, deterministic gratings with periods down to 330 nm and modulation depths of more than 100 nm are fabricated on tool steel and stainless steel. Areas of up to $5\,\mathrm{mm}\times 13\, $ mm can be processed without stitching errors.     

Quasi-Talbot effect of the sub-wavelength Ag grating

When a TM-polarized beam incidents normally on a thick sub-wavelength Ag grating with small opening ratio, self-images form in the transparent dielectric layer due to contributions not only from waves radiating from the slits, but also from the Surface Plasmons (SPs) created on Ag surface. These two contributions make the self-images connect together along the propagation direction and form continuous stripes with period equal to half of that of the grating. We define this phenomenon as quasi-Talbot effect. For a thin sub-wavelength Ag grating or a grating with large opening ratio, its intensity distribution conforms to the conventional Talbot effect. Investigation on quasi-Talbot effect of sub-wavelength metal grating can develop new applications in nano-scale devices.     

Optimized sub-wavelength grating mirror design for mid-infrared wavelength range

Several designs of sub-wavelength grating mirrors adapted to mid-infrared operation are reported with several percents of tolerance for the grating fabrication. These designs have been automatically optimized by the use of a genetic-based algorithm to maximize a quality factor defined to meet the requirements of a VCSEL cavity mirror. These mirrors are devoted to integration in VCSEL operating near λ=2.3 μm, with a large bandwidth, very high reflectivity coefficient for transverse magnetic mode only, polarization selectivity and a thickness as low as 2 μm.     

High-transmittivity non-periodic sub-wavelength high-contrast grating with large-angle beam-steering ability

We present a high-transmittivity non-periodic sub-wavelength high-contrast grating （HCG） with large-angle beam-steering ability for transmitted light. The phase front profile of transmitted light is a decisive factor to the beam-steering property of the HCG. By designing the structural parameters of the HCG, both beam steering and high transmittivity can be achieved. The properties of the beam steering and transmission are numerically studied with the finite element method. The results show that the transmittivity is up to 0.91 and the steering angle is 27.42° which is consistent with the theoretical 30°.     

Extraordinary optical transmission for TE wave through metallic sub-wavelength grating with slits filled with dielectric

A metallic sub-wavelength grating with slits filled with dielectric was proposed to achieve broadband and enhanced Extraordinary Optical Transmission (EOT) for Transverse Electric (TE) wave. The physical mechanism for the improvements of the transmission spectrum was also revealed. It was found that the Fabry–Perot cavity resonance in the grating slits was the cause of the enhancement of the EOT and the waveguide modes theory was the fundamental mechanism for the broadened bandwidth of the transmission.     

New method of increasing diffraction efficiency of grating transferred in glass substrate by corona-charging treatment

We propose a new method of increasing the diffraction efficiency of a glass substrate onto which a grating structure has been transferred by corona-charging treatment. The first-order diffraction efficiency was successfully increased by at least 100-fold by a simple low-cost process in which an aqueous solution prepared from poly(vinyl alcohol) (PVA) and glucose was spin-coated on the glass substrate. As the solution dried, the spin-coated film formed a periodic surface relief grating with the period corresponding to that of the grating transferred to the glass substrate. The period and depth of the relief structure were 50 and 1.4 μm, respectively. The depth of the relief structure strongly depended on the concentrations of PVA and glucose in the solution. Under our experimental conditions, a high first-order diffraction efficiency was obtained when the PVA concentration was 7.5–8 wt% and the glucose concentration was 30–45 wt %.     

Fano resonance sensing based on coupled sub-wavelength dielectric grating and periodic photonic crystal

Based on the diffraction effect of sub-wavelength dielectric grating and the optical property of periodic photonic crystal, a hybrid structure of sub-wavelength grating all-dielectric multilayer thin film containing periodic photonic crystal is proposed. The transmission property of the structure is simulated by finite element method (FEM). The result shows that the discrete state generated by the sub-wavelength waveguide grating will be coupled with the continuous state generated by the photonic crystal cavity and the Fano resonance can be formed. The Fano resonance sensing model based on structural parameters and resonance wavelength are established, the influence of structural parameters on the Fano resonance spectral curve is quantitatively analyzed by numerical simulations, and the dynamic detection of the refractive index of samples is realized. The above structure can realize the optical refractive index sensing with high figure of merit (FOM) value and provide an effective theoretical reference for the formation of Fano resonance in the all-dielectric hybrid structure.     

Metal grating on a substrate nanostructure for sensor applications

Extraordinary optical transmission via periodic array of sub-wavelength slits in a metal layer on a dielectric substrate is revisited for sensing applications. Numerical case studies using an in-house software tool showed two peaks of enhanced transmission, one being very sensitive to the ambient index and another to the substrate index. Based on this, we designed and realized an optical sensor with sensitivity of the order of 400 nm/RIU.     

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。