基于导模共振效应的多通道窄带滤光片的设计

基于导模共振效应设计了几种多通道窄带滤光片,并利用严格耦合波法分析其光谱特性。在设计的单层滤光片的基础上增加第一层高折射率缓冲层,当厚度为523.8 nm和689.2 nm时,得到双通道和三通道的反射峰,在此基础上增加第二层厚度为768 nm的低折射率缓冲层,得到四通道的反射峰。另外,通过调节单层滤光片的入射角度得到对称的双通道反射峰。     

1064 nm负滤光片的设计与制备北大核心CSCD

针对当前可见-近红外光电探测器的激光防护要求,研究了1064 nm负滤光片的设计和制备。基于等效折射率理论,综合考虑光谱和场强分布优化,设计了由SiO2/Y_(2)O_(3)/H4组合的规整膜系和SiO2/H4组合的非规整膜系负滤光片;采用离子束辅助热蒸发沉积方式对负滤光片进行了制备,并测试了其光学和抗激光损伤性能。结果表明:在膜系结构G|(0.5LH0.5L)s|A两侧匹配减反膜可以有效减小通带波纹,调整膜系最外层厚度可以同时改善膜系的光谱特性和电场强度分布。镀制的规整膜系负滤光片在400~900 nm和1200~2000 nm波段平均透过率分别为89.98%和93.21%,1064 nm透过率为1.29%,激光损伤阈值为6.0 J/cm^(2);非规整膜系负滤光片在650~900 nm和1200~2000 nm波段平均透过率分别为93.70%和94.99%,1064 nm透过率为1.60%,激光损伤阈值为6.8 J/cm^(2)。     

10.4μm～12.5μm带通滤光片的设计

根据等效折射率理论设计了由 Ｐｂ Ｔｅ 和 Ｚｎ Ｓ 多层膜组成的１０ ．４ μｍ ～１２ ．５ μｍ 带通滤光片；研究了该滤光片的光谱特性； 提出了一种压缩通带内波纹幅度的简易方法。结果表明： 利用此方法在等效折射率设计的基础上，能有效抑制带通内波纹幅度的大小，可获得良好的光谱性能。     

1064nm导模共振滤光片的设计与分析

为了获得峰值波长为1 064 nm的反射型窄带滤光片,采用导模共振原理进行设计,并利用严格耦合波法对滤光片的光谱特性进行了理论分析。首先设计了峰值波长1 064 nm单层反射型导模共振滤光片,由于覆盖层和基底层的折射率不匹配,使得远离峰值波长处的反射率偏高,引入减反射层后,峰值波长两侧的反射率明显降低;其次分析了光栅层厚度、光栅周期对滤光片光谱性能的影响。结果表明设计的滤光片具有反射率高、带宽窄及旁带反射率低等优良的光学性能。     

基于遗传算法的超分辨多元环形滤光片设计

本文研究利用光学超分辨技术提高光盘存储密度.给出了一种可以达到衍射超分辨力的多元环形滤光片的设计结果.介绍了该多元环形滤光片的理论设计方法.之后用遗传算法设计了多组多元环形滤光片的结构参数,模拟结果显示设计的环形滤光片能使横向的半峰全宽半径值减小30%,达到提高信息存储密度的目的.另一方面该环形滤光片能使焦深不变或变长,减小了在记录过程中因为光盘的微小波动而引起的记录信息的错误率.     

基于TiO_2/SiO_2材料的短波通滤光片的设计与制备

根据短波通滤光片的设计原理,采用二氧化钛和二氧化硅作为高折射率材料和低折射率材料,从理论上计算出用这两种材料设计的短波通滤光片所需要的周期数及主膜系,并用膜系设计软件对该膜系进行优化。依照改进的设计,采用电子束蒸发的方法制备出符合要求的短波通滤光片,并找到最佳制备工艺和方法。UV-3100分光光度计测量结果表明,在波长380-670nm处,平均透射率T90%;在波长690-800nm处截止,平均透射率T1%,镀制膜层的透射率曲线与理论曲线符合技术要求。     

中波红外短波通滤光片的设计与镀制技术研究

研究了中波红外宽光谱短波通滤光片优化设计和镀制,论述了设计该种滤光片的原则和方法。根据等效折射率理论,以周期性对称膜系为基础,使用部分膜层优化方法,设计了中波红外宽光谱短波通滤光片,在2 300～4 700 nm透射波段范围上的平均透射率设计值大于90%,在5 000～6 300 nm截止波段范围上的平均透射率小于1.00%。采用"会聚光红外光学系统"和等离子体辅助沉积工艺实验制备了滤光片。实验表明,在透射波段范围上的平均透射率约为83%,截止波段的平均透射率约为0.45%。结果表明,部分膜层优化方法设计的膜系,膜层结构简单,有利于膜层厚度的监控。     

一种长波红外宽光谱长波通滤光片的设计与镀制

长波红外宽光谱长波通滤光片是光谱成像技术中重要的光学元件。本文研究了一种宽光谱长波通滤光片优化设计,论述了设计长波红外宽光谱长波通滤光片的设计原则和方法。根据等效折射率理论,以周期性对称膜系为基础,使用压缩透射区内波纹幅度的部分膜层优化方法,设计了满足性能指标要求的长波红外长波通滤光片。经过优化,所设计的膜系高透射波段内的平均透射率大于90%,高透射区内的最低透射率也高于85%。截止波段内的平均透射率小于1%,截止区内的最高透射率也低于5%。研究表明,部分膜层优化方法设计的膜系,膜层结构简单,有利于膜层厚度的监控,既能克服全自动优化方法给工艺上带来的困难,又弥补了解析法设计膜系时不能调整光谱特性的不足。     

负折射率材料可控效应及结构设计

控制电磁波的传播方向,甚至控制包括光波在内的波的传播方向,是一个充满前景的研究方向.本文对可控负折射率材料进行了研究,利用折射率的变化则可以实现波方向上的可控.根据对双金属环阵列结构产生负磁导率特性的分析,研究了该结构金属环局部开口状态至局部闭合状态导致的磁导率及最后导致折射率的变化,发现开闭口出现的不同特性,设计了双金属环局部闭合状态阵列可控结构的方案.分别对开口金属环阵列和局部闭合金属环阵列进行磁导率及它们与金属带组合结构折射率的实验,与理论结果相比较,并且对本文所设计的可控负折射率阵列结构进行了验证.最终结果证明,通过设计的这个结构,可以实现某一微波波段波传播的两个方向的控制,同时本文的实验结论也证明了利用折射率的改变来控制波的传输方向是可行的.应用合理的结构,通过操控电场,可以实现在波在方向上的改变.这对于研究和工程应用都有着可行的巨大潜力.     

反射型和透射型导模共振滤光片的设计

本文设计了中心波长为1315 nm的反射型和透射型导模共振滤光片,并利用严格耦合波法分析了其光谱特性。首先设计了中心波长1315 nm单层反射型导模共振滤光片,但由于覆盖层和基底层的折射率不匹配,使得远离中心波长处的反射率偏高,引入减反射层设计后,中心波长两侧的反射率明显降低。其次设计了中心波长1315 nm的透射型导模共振滤光片,分析了光栅层厚度对中心波长位置的影响。用严格耦合波法计算表明,设计的反射型和透射型导模共振滤光片具有优良的光谱性能。     

Oxidation of evaporated porous silicon rugate filters

Rugate filters are thin-film optical interference coatings with sinusoidal variation of the refractive index. Several of these filters were fabricated with glancing angle deposition, which exploits atomic competition during growth to create nanoporous materials with controllable effective refractive index. This method enables the fabrication of devices with almost arbitrary refractive index profiles varying between the ambient, 1.0, and the index of the film material, in this case silicon with an index of 4.0 (at 600 nm). As these filters are inherently porous, oxidation of the silicon can occur throughout the device layer, and here we study the intentional oxidation of silicon filters by high-temperature reaction with gaseous oxygen. We find that a significant portion of the silicon filter oxidizes in approximately 10 min when heated to 600 degrees C-650 degrees C in an oxygen environment; oxidation then continues slowly over several hours. The presence of water vapor has little apparent effect on the oxidation reaction, and attempts to oxidize with ozone at room temperature were unsuccessful. As silicon filters oxidize to become silica, spectral blueshifts and increased short-wavelength transmittance are observed. Measured and calculated transmittance spectra generally agree, although the lack of absorption and dispersion in the theoretical model limits detailed comparison.     

Advanced key technologies for magnetron sputtering and PECVD of inorganic and hybrid transparent coatings

Besides classical multilayer systems with alternating low and high refractive indices, reactive pulse magnetron sputtering processes offer various possibilities of depositing gradient films with continuously varying refractive index. Using nanoscale film growth control it is possible to achieve optical filter systems with a defined dependency of refractive index on film thickness, e.g. by sputtering a silicon target in a time variant mixture of oxygen and nitrogen. Also reactive co-sputtering of different target materials such as silicon and tantalum in oxygen is suitable as well. Rugate filters made from SiO_xN_y or Si_xTa_yO_z gradient refractive index profiles find their application in spectroscopy, laser optics and solar concentrator systems.Furthermore polymer substrates are increasingly relevant for the application of optical coatings due to their mechanical and economical advantages. Magnetron PECVD (magPECVD) using HMDSO as precursor allows to deposit carbon containing films with polymer-like properties. Results show the suitability of these coatings as hard coatings or matching layers. Multifunctional coatings with antireflective and scratch-resistant properties were deposited on polymer substrates using a combined magPECVD and sputter deposition process.     

Elastic and plastic relaxation of densified SiO2 films

Ion- and plasma-assisted deposition has been extensively used for the fabrication of high-performance optical films with dense and smooth microstructures that are essential for applications such as low-loss and environmentally stable optics. SiO(2) is a well-known amorphous material suitable for energetic deposition. SiO(2) single layers and SiO(2)-based single-cavity narrow-bandpass filters were prepared by plasma-ion-assisted deposition. The refractive index and film thickness were determined by variable-angle spectroscopic ellipsometry. The high compressive stress of the densified film was correlated to increased packing density. The center wavelength shift of the narrow-bandpass filters as a function of sample-temperature as well as high-temperature annealing was determined via spectral transmission measurement. Structural relaxation of the densified SiO(2) films was observed from the variation of the refractive index and physical thickness for the single layers and the center wavelength shift for the narrow-bandpass filters, suggesting elastic and plastic deformation of the densified films corresponding to a reversible and an irreversible center wavelength shift, respectively.     

Dichroic rugate filters

We reduce the sidelobes that are present in the bandpass zones of rugate filters, using antireflection coatings to design dichroic rugate filters. Our designs are based on the formalism of equivalent systems that allow us to consider a rugate filter a simple equivalent layer with equivalent optical admittance and equivalent phase thickness functions. Rugate filters with apodization were considered.     

Calculation of film thickness for dip coated antireflective films

Antireflective films require an accurate film thickness to be able to perform optimally. The ideal thickness on most films is a quarter wavelength optical thickness (QWOT). The physical thickness of the QWOT film depends on the refractive index of the material that is being used. Each layer of the antireflective coating will have different optimal conditions for applying the film. When using the dip coating method, these conditions are withdrawal speed and concentration of solution.When using the currently accepted equations derived by Yang et al. to calculate the film thickness an error of 31.7% was noted when compared with the experimentally measured film thickness. Realising that the refractive index of the film plays a role in determining the thickness of the film, the equations were modified to take refractive index into account. Once this was taken into account, the calculated film thickness deviated from the measured film thickness by 8.7%. This error can be attributed to experimental errors which involve temperature and concentration fluctuations.     

测量薄膜折射率的光栅衍射干涉方法

根据光的干涉理论,讨论了条纹周期数对测量薄膜折射率不确定性的影响,推导出干涉条纹错位量与薄膜折射率和厚度的关系式。由此提出采用光栅衍射干涉测量薄膜折射率的方法和实验方案。实验表明:该方法的干涉条纹测量精度达λ/10~λ/20,薄膜折射率测量精度可达 0.01 以上。     

多光谱带通线性渐变滤光片的研制

线性渐变滤光片是一种特殊的滤光片,它的中心波长是随着在滤光片上位置的不同而变化的.采用离子束辅助沉积技术研制的线性渐变滤光片在0.4～1.1 μm波段有10通道,平均透射率从77.5%增加到97.4%,在基板的中间任一位置只透过0.4～1.1 μm内的一种特定波长的光.同时讨论了膜厚均匀性对线性渐变滤光片光谱性能的影响,计算表明镀制线性渐变滤光片时,在一定的配置下基片具有最佳的尺寸大小.     

三层亚波长光栅结构的透射特性

设计了一种具有三层结构的亚波长金属光栅,采用时域有限差分（FDTD）法对所设计的三层光栅结构进行仿真计算．与单层金属光栅相比,这种三层的光栅结构具有更好的滤波效果,其透射光谱中峰值可达77％,且能很好地抑制高波段的透射率．分析了各几何参数对所设计的光栅结构透射特性的影响,尤其是对透射光谱中0值位置的影响．结果表明0值位置主要受光栅缝宽、介质层高度和介质折射率的影响,而与金属层光栅的高度无关．其影响规律为偏振滤波器的设计提供了参考．     

Surface enhanced absorption and transmission from dye coated gold nanoparticles in thin films

Absorption spectra of gold nanoisland thin film and the composite film of gold having thin coating of Methylene Blue and Rh6G dyes have been studied. Thin gold nanoisland film shows surface plasmon resonance (SPR) peak in the visible wavelength range, which shifts to near infrared with an increase in the thickness of the film. It was found that thin film of gold consists of nanoparticles of different size and shape, particularly nanorods of noncylindrical shapes. A linear relation was found between SPR peak wavelength and the aspect ratio of the nanoparticles in gold thin film. Effective medium refractive index of the gold film is estimated to be ~2.5, which decreases with an increase in film thickness. The coating of dyes on gold films splits the SPR peak with an enhanced absorption. Enhancement in absorption of composite film is maximal when the dye absorption peak coincides with the SPR peak; otherwise enhancement in transmission is observed for all the wavelength range. Absorption amplitude of composite film peaks increase with an increase in the gold film thickness, which tend toward saturation for film thickness of ≥6 nm. A correlation shows that absorption spectra can be described by the Maxwell Garnett theory, when the gold nanoparticles have a nearly spherical shape for very thin film (≤6 nm).     

Multilayer antireflective and protective coatings comprising amorphous diamond and amorphous hydrogenated germanium carbide for ZnS optical elements

To effectively protect and improve the transmittance of ZnS optical elements in the far infrared band, combined amorphous diamond (a-D) and amorphous hydrogenated germanium carbide (a-Ge_1−xC_x:H) films have been developed. The optical interference coatings were designed according to the layer optics theory. The a-D films, of which refractive index and film thickness were controlled by changing substrate bias and deposition time respectively, were deposited by filtered cathodic vacuum arc technology. The a-Ge_1−xC_x:H films were prepared by radio frequency sputtering technology. During this process their refractive index was modulated by changing the gas flow rate ratio and their film thickness was controlled by the flow rate ratio and deposition time. It has been shown that the combined films are superexcellent antireflective and protective coatings for ZnS optical elements.