密集波分复用薄膜滤光片的群延迟补偿设计

设计了一种基于薄膜干涉理论的反射式相位补偿器件，用以补偿密集型波分复用窄带滤光片所产生的群延迟，使50GHz薄膜滤光片的群延迟特性适应于40Gb／s系统的要求，在0．2nm带宽下群延迟波动从10ps左右下降到0．76ps以下。     

短波通滤光片膜系设计

详细介绍用等效折射率概念设计短波通滤光片的原理和计算方法。根据原理和方法，选择二氧化钛（TiO2）作为高折射率材料、二氧化硅（SiO2）作为低折射率材料。首先从理论上计算出用这2种材料设计的波长λ=950～1150nm的短波通滤光片所需要的周期数，然后给出短波通滤光片的主膜系和光谱曲线。由于据此周期数设计出的膜系光谱曲线在750～810nm处的透过率不符合要求，因此对该膜系进行了改进。依照改进的设计进行多次制备，最终制备出了符合要求的短波通滤光片，找到了最佳制备工艺和方法。最后，对制备出来的短波通滤光片薄膜进行了各种环境实验。实验结果表明，膜层的各项指标符合设计要求。     

弱吸收多层薄膜消光系数的反演

从窄带干涉滤光片的峰值透射率测量可以直接反演出弱吸收薄膜的消光系数，从而得到一种能简易而又精确地评价多层薄膜微弱吸收的新方法. 推导了弱吸收窄带干涉滤光片的吸收表达式， 阐述了确定弱吸收薄膜消光系数的基本原理.以离子束溅射的Ta₂O5/SiO₂波分复用滤光片为例，分析了这种评价方法的基本精度. 关键词： 光学测试 离子束溅射 光学薄膜干涉滤光片 消光系数     

基于遗传算法的斜入射窄带滤光片膜系优化设计

根据薄膜窄带滤光片在斜入射时的偏振特性,提出了基于遗传算法的斜入射薄膜窄带滤光片膜系优化设计方法.根据开发的程序,设计并制备了一组可用于18°倾斜入射的0.8纳米信道间隔的五腔薄膜窄带滤光片.该滤光片能有效地抑制斜入射时偏振光中心波长的分离现象,降低器件的偏振相关损耗,通过角度调谐能实现选择波长的改变.通过与针法设计的滤光片膜系相比,遗传算法得到的膜系具有更高的矩形度、更大的波长调谐范围以及更低的偏振相关损耗.实验结果表明其满足设计要求并有超过25纳米的波长调谐范围.     

薄膜法布里-珀罗滤光片中反射高斯光束分裂现象

提出了一种模拟薄膜法布里-珀罗滤光片中反射光束分裂现象的方法.根据反射率曲线，简单解释了产生这个现象的原因.实验上制备了薄膜法布里-珀罗滤光片，观察和测量了反射光束分裂的现象，理论计算基本与实验结果符合. 关键词： 薄膜 法布里-珀罗 光束分裂     

连续激光辐照ZnSe/MgF2/K9滤光片的透射特性研究

 分析了连续激光辐照ZnSe/MgF₂/K9滤光片引起透射特性的变化。在室温条件下，用波长0.632 8μm激光作为探测光束，测量了1.06μm连续激光辐照ZnSe/MgF₂/K9滤光片温升引起薄膜折射率的改变，导致探测光束通过干涉滤光片后透过率的热致非线性变化。在光斑直径0.75mm条件下，测量了不同功率激光辐照ZnSe/MgF₂/K9滤光片引起温升随时间的变化。在激光功率30W，辐照时间2.52s条件下，实验观测到ZnSe/MgF₂/K9滤光片薄膜破坏温度约为90℃，辐照时间10s时干涉滤光片形成的薄膜龟裂形貌。     

微缺陷对薄膜滤光片环境稳定性的影响

用热蒸发方法沉积了薄膜滤光片.并将样品分别在去离子水中浸泡10天和30天.通过分光光度计、光学暗场显微镜、及扫描电子显微镜等多种测试手段,对诱导透射滤光片在潮湿环境下的稳定性进行了研究.实验发现,在潮湿环境下滤光片产生的膜层分离都是从薄膜中微缺陷点处开始发生和发展的,微缺陷是影响滤光片环境稳定性的重要原因之一,其中杂质和针孔是滤光片中两种最常见的微缺陷.EDS能谱分析进一步表明,薄膜中杂质缺陷成分即为Al2O3膜料本身,所以不能推测,薄膜沉积中的喷溅可能是微缺陷产生的根本原因,抑制喷溅可以有效提高薄膜滤光片的环境稳定性.最后还用扩散理论对微缺陷引起滤光片失效的机理进行了分析.     

用于倾斜入射的波分复用薄膜滤光片的特性及改进

对倾斜入射时窄带薄膜滤光片的特性作了描述 ,由于低折射率间隔层的滤光片 ,倾斜入射时 p偏振分量的通带比s分量更移向短波 ,而高折射率间隔层的滤光片则反之 ,因此可把间隔层同时设计成高、低折射率两种材料 ,或选用适当的中间折射率材料 ,使p分量和s分量两个通带的中心波长重合。设计了用于 2 0°入射角的密集波分复用 (DWDM )滤光片 ,并给出了实验结果。     

波分复用薄膜带通滤光片的中心波长温度稳定性

讨论了影响波分复用薄膜滤光片中心波长漂移的因素 ,着重分析了滤光片的温度稳定性。根据实验结果 ,借助于高桥模型 ,分析计算了滤光片的折射率温度系数、线膨胀系数和泊松比以及它们对温度漂移的影响。得到了Ta2 O5/SiO2 滤光片薄膜的折射率温度系数、线膨胀系数、泊松比分别为 1× 10 -5℃-1,5× 10 -7℃-1和 0 12 ,指出了这三个参量是影响温度稳定性最重要的因素 ,特别是薄膜的折射率温度系数。对特定的基板热膨胀系数 ,通过调节滤光片的干涉级次和间隔层材料 ,可望得到零温度漂移的稳定滤光片。     

致冷多层干涉滤光片的光学特性

本文系统地研究了红外多层干涉滤光片的低温特性、并从薄膜的基本光学特性出发,推导了窄带滤光片、截止滤光片透射率与波长的温度效应.给出了截止滤光片截止波长的温度漂移公式.     

不同后处理方法对溶胶-凝胶SiO2膜层抗污染能力的影响

以正硅酸乙酯作为前驱体,利用碱催化方式制备了SiO2溶胶,采用提拉法在K9基片上镀制SiO2单层薄膜,分别用热处理、紫外辐射处理、氨水加六甲基二硅胺烷气氛处理和酸碱复合膜4种后处理法对膜层进行处理,采用分光光度计、红外光谱、扫描探针显微镜、静滴接触角测量仪、椭偏仪等分析了薄膜的特性,通过真空环境加速污染实验对处理前后的膜层进行抗污染能力对比,结果表明:在碱性SiO2膜层上加镀一层酸性SiO2膜的复合膜层整体透过率仍保持在99%以上,疏水角达到128°,膜层真空抗污染能力大大加强。     

多通道光谱采集系统滤光片设计方法研究

普通彩色相机加载宽带滤光片构造的多通道光谱采集系统的光谱重建性能与滤光片的选用密切相关。针对上述问题,提出基于主成分分析法的合成滤光片设计方法,旨在获得具有较高光谱重建性能并对所有图像场景均适用的最优滤光片组合。在收集多个宽带滤光片的基础上,测得其透射率并转换成矩阵形式;采用主成分分析方法提取该矩阵的前2个主成分,标准化处理后的主成分即为所求合成滤光片的透射率。为了验证上述方法获得的滤光片的性能,利用色差和光谱均方根误差2个指标对加载了合成滤光片的仿真采集系统的光谱重建精度进行了评价。实验结果表明:采用该方法得到的滤光片组合优于常用方法得到的滤光片组合, 用其构造的成像系统具有较高的色度重建精度和光谱重建精度,此外,改变目标场景颜色特性,其重建性能保持稳定。     

Microelectromechanical bandpass filters based on cyclic coupling architectures

Bandpass filters based on resonant microelectromechanical systems (MEMS) have the unique advantage of being able to leverage the benefits of classical mechanical filters, including their high quality factors of resonance, while simultaneously addressing the challenges associated with manufacturing cost and size, and enabling integrated fabrication with other on-chip components. While prior research has demonstrated the benefits of microelectromechanical filters composed of both isolated and coupled microresonators, the optimality of existing filter architectures, and their associated performance metrics, is yet to be fully determined. To this end, the current effort seeks to investigate the relative utility of micromechanical filter designs which exploit a nontraditional filter architecture founded upon cyclic, elastic coupling. Specifically, the work seeks to characterize the pertinent performance metrics and robustness characteristics associated with these systems, and to benchmark the acquired results against conventional, open-chain filter designs. The work ultimately demonstrates that MEMS filters based upon cyclic coupling architectures may be beneficially leveraged in certain filter implementations to improve overall system performance.     

Two-zone pupil filters

The performance of pupil filters consisting of two zones each of constant complex amplitude transmittance is investigated. For filters where the transmittance is real, different classes of potentially useful filter are identified and optimized. These include leaky filters with an inner zone of low amplitude transmittance, pure phase filters with phase change of π, and equal area filters. The first of these minimizes the relative power in the outer rings for a given axial resolution, the second maximizes the Strehl ratio for a given transverse resolution, and the third minimizes the relative power in the outer rings for a given transverse resolution. Complex filters can give an axially shifted maximum in intensity: the performance parameters calculated relative to the true focus are investigated for some different classes of filter, but filters with phase change not equal to π are found to give inferior performance to the real value filters.     

Three-zone pupil filters

The performance of pupil filters consisting of three zones each of constant complex amplitude transmittance is investigated. For filters where the transmittance is real, different classes of potentially useful filter are identified. These include leaky filters with an inner zone of low amplitude transmittance, pure phase filters with phase change of π, and equal area filters.     

Design of a Composite Wavelet Matched Filter Using Breeder Genetic Algorithm

We outline a method to design a composite wavelet matched filter using the breeder genetic algorithm. The composite filter consists of a linear combination of wavelet and matched filters. Breeder genetic algorithm has been used to find the optimal weighting coefficients for the wavelet and the matched filters that constitute the composite filter. For the breeder genetic algorithm, the geometric mean has been used as the crossover operator and the creep has been used as the mutation operator. The performance of the filter is tested in the presence of additive white Gaussian noise. The performance of the composite wavelet matched filter has also been compared with that of the phase only filter and the classical matched filter. The designed filter can be used in an optical correlator to separate two classes of input images for fingerprint-based user identification in security systems.     

Performance analysis of WDM-PON architecture using different receiver filters

In this paper the performance effect of a 40 Gb/s Wavelength-Division-Multiplexed Passive Optical Network (WDM-PON) is analyzed using different receiver filters namely Integrator filter, Bessel filter, Butterworth filter, Chebyshev filter, Inverse Chebyshev filter, Elliptic filter, Gaussian filter and Rectangular filter. The data rate and channel spacing are taken as 10 Gb/s per channel and 100 GHz, respectively. Among all the investigated filters, Bessel filter is considered to be the best one for WDM-PON network by the obtained BER and Q factor values.     

Frequency multiplexed DOG filter

In order to improve optical correlation performance, a multiplexed DOG (MDOG) filter is constructed from two Difference of Gaussian (DOG) filters, one DOG filter is tuned for noise robustness and the other for accurate object localization. The filter's performance is compared with the CMF, POF and single DOG filter.     

Pupil apodization for increasing data storage density

We introduce a technique for increasing density in optical data storage systems. This technique is based on the use of a superresolving filter at the pupil of a confocal readout system. The main characteristic of this confocal readout system is that the light beam traverses twice through the pupil filter. We describe how to analyze the system performance for general filters, but we focus the study on filters with no focus displacement. Although the storage density attainable depends on the filter characteristics, we show that the storage density can be easily duplicated.     

Denoising 3D MR images by the enhanced non-local means filter for Rician noise

The non-local means (NLM) filter removes noise by calculating the weighted average of the pixels in the global area and shows superiority over existing local filter methods that only consider local neighbor pixels. This filter has been successfully extended from 2D images to 3D images and has been applied to denoising 3D magnetic resonance (MR) images. In this article, a novel filter based on the NLM filter is proposed to improve the denoising effect. Considering the characteristics of Rician noise in the MR images, denoising by the NLM filter is first performed on the squared magnitude images. Then, unbiased correcting is carried out to eliminate the biased deviation. When performing the NLM filter, the weight is calculated based on the Gaussian-filtered image to reduce the disturbance of the noise. The performance of this filter is evaluated by carrying out a qualitative and quantitative comparison of this method with three other filters, namely, the original NLM filter, the unbiased NLM (UNLM) filter and the Rician NLM (RNLM) filter. Experimental results demonstrate that the proposed filter achieves better denoising performance over the other filters being compared.