Optical transfer function analysis of circular-pupil wavefront coding systems with separable phase masks

This paper proposes a simple method to achieve the optical transfer function of a circular pupil wavefront coding system with a separable phase mask in Cartesian coordinates. Based on the stationary phase method, the optical transfer function of the circular pupil system can be easily obtained from the optical transfer function of the rectangular pupil system by modifying the cut-off frequency and the on-axial modulation transfer function. Finally, a system with a cubic phase mask is used as an example to illustrate the way to achieve the optical transfer function of the circular pupil system from the rectangular pupil system.

An apodized cubic phase mask used in a wavefront coding system to extend the depth of field

The point spread function(PSF)caused by a wavefront coding system with a cubic phase mask has big side-lobes which leads to bad image restoration.This paper proposes a novel apodized cubic phase mask to suppress the side-lobes of the PSF.Simulated annealing algorithm is used to optimize the cubic and the truncation parameter of the phase mask.The system with the novel phase mask has better performance in the modulation transfer function(MTF)especially in low-and-medium spatial frequency region.The simulation results show that the restored images with the novel phase mask are superior to the one with the classic cubic phase mask in contrast and ringing effect.The experimental results show that the side-lobes of the PSF are suppressed by using the apodized cubic phase mask.

Occurrence of Features of Fiber Bragg Grating Spectra Having a Wavelength Corresponding to the Phase Mask Periodicity

The use of a phase mask with 536 nm uniform pitch allowed the fabrication of a fiber Bragg grating for use at a Bragg wavelength of 785 nm. Reflection and transmission features at 1552 nm, twice the Bragg wavelength, associated with the phase mask periodicity were observed. However, when phase mask orders other than ＋1 were absent during fabrication the features at 1552 nm were not evident.

Simple PSF based method for pupil phase mask’s optimization in wavefront coding system

By applying the wavefront coding technique to an optical system, the depth of focus can be greatly increased. Several complicated methods, such as Fisher Information based method, have already been taken to optimize for the best pupil phase mask in ideal condition. Here one simple point spread function (PSF) based method with only the standard deviation method used to evaluate the PSF stability over the depth of focus is taken to optimize for the best coefficients of pupil phase mask in practical optical systems. Results of imaging simulations for optical systems with and without pupil phase mask are presented, and the sharpness of image is calculated for comparison. The optimized results showed better and much more stable imaging quality over the original system without changing the position of the image plane.

Energetic few-cycle pulse compression in gas-filled hollow core fiber with concentric phase mask

The compression of high-energy, linearly polarized pulses in a gas-filled hollow core fiber(HCF) by using a concentric phase mask is studied theoretically. Simulation results indicate that using a properly designed concentric phase mask, a40-fs input pulse centered at 800 nm with energy up to 10.0 mJ can be compressed to a full width at half maximum(FWHM) of less than 5 fs after propagating through a neon-filled HCF with a length of 1 m and diameter of 500 μm with a transmission efficiency of 67%, which is significantly higher than that without a concentric phase mask. Pulses with energy up to 20.0 mJ can also be efficiently compressed to less than 10 fs with the concentric phase mask. The higher efficiency due to the concentric phase mask can be attributed to the redistribution of the transverse intensity profile, which reduces the effect of ionization. The proposed method exhibits great potential for generating few-cycle laser pulse sources with high energy by the HCF compressor.

Deblurring,artifact-free optical coherence tomography with deconvolution-random phase modulation

Deconvolution is a commonly employed technique for enhancing image quality in optical imaging methods.Unfortu-nately,its application in optical coherence tomography(OCT)is often hindered by sensitivity to noise,which leads to ad-ditive ringing artifacts.These artifacts considerably degrade the quality of deconvolved images,thereby limiting its effect-iveness in OCT imaging.In this study,we propose a framework that integrates numerical random phase masks into the deconvolution process,effectively eliminating these artifacts and enhancing image clarity.The optimized joint operation of an iterative Richardson-Lucy deconvolution and numerical synthesis of random phase masks(RPM),termed as De-conv-RPM,enables a 2.5-fold reduction in full width at half-maximum(FWHM).We demonstrate that the Deconv-RPM method significantly enhances image clarity,allowing for the discernment of previously unresolved cellular-level details in nonkeratinized epithelial cells ex vivo and moving blood cells in vivo.

Writing Fiber Grating of Different Wavelength Using the Same Phase Mask

Chirped fiber grating was used in dispersion compensator. We tried to use the same phase mask to write fiber grating of different wavelength with two methods to reduce the price of the fiber grating.

Modal analysis of the 0th order nulled phase masks

A simple modal analysis （MA） method to explain the diffraction process of 0th order nulled phase mask is presented. In MA, multiple reflections of the grating modes at grating interfaces are considered by introducing equivalent Fresnel coefficients. Analytical expressions of the diffraction efficiencies and modal guidelines for the 0th order hulled phase grating design are also presented. The phase mask structure, which comprises a high-index contrast HfO2 grating and a fused-silica substrate, is optimized using rigorous coupled-wave analysis around the 800-nm wavelength, after which the modal guideline for cancellation of the 0th order in a phase mask is verified. The proposed MA method illustrates the inherent physical mechanism of multiple reflections of the grating modes in the diffraction process, which can help to analyze and design both low-contrast and high-contrast gratings.

Trapezoidal phase mask coronagraph

An angular trapezoidal phase mask used for a wideband coronagraph is proposed. The azimuthal phase of the mask is double-periodic and has both trapezoidal and constant parts in each period. This kind of continuous phase distribution can be employed to avoid the abrupt phase variation of the 6-level phase distribution we proposed previously. Numerical calculations show that this more practical phase mask can still keep its superior performance in terms of starlight elimination, small inner working angle, and good achromatism. It is of great importance that there is no singularity in this kind of mask except for a singularity at the center. This mask design is close to real manufacturing conditions, and the process technology is superior.

Intelligent System for Mask Phase-Shifter Design

讨论了一个用于相移掩模智能设计的专家系统。这个系统包括输入输出系统，仿真系统，知识库系统，人—机接口，黑板系统。它有一个包括图形获取、预处理、模式抽取、搜索与解释、图形复合与输出等环节的工作过程。系统的软件实现运用了面向对象的表示方法。

Periodic surface structures fabricated by one excimer laser pulse through a silica phase mask grating

RECENTLY, excimer laser devices, which have higher-energy density output in pulsed ultravio-let (UV) light (193 or 248 nm), have been employed to generate some thin film struc-tures. The principle of this technique, which is also called pulsed laser deposition (PLD)technique, is that the exposed material could be ablated out of the sample by the focusing laserbeam, and redeposit on a substrate to form thin-film structures under certain conditions. Onthe other hand, researchers have obtained high-quality Bragg gratings in photosensitive

基于长度可变密钥的光学图像加密方法

为提升光学图像加密效果,设计了一种基于长度可变密钥的光学图像加密方法。基于混沌方程构成混沌序列均匀化普适算法,运用该算法生成均匀化伪随机序列,以此作为长度可变密钥,经空间光调制器调制后,转换此类密钥为伪随机相位掩模(PRPM),运用两个转换后PRPM双重随机相位编码初始光学图像,并结合变形分数傅里叶变换(AFrFT),相位转换编码后光学图像,获得加密光学图像,完成光学图像加密。实验结果显示,该方法可针对不同光学图像生成敏感性与唯一性密钥,实现不同光学图像的加密处理,加密效果显著,加密光学图像的像素频数分布均匀,且解密后光学图像与初始光学图像几乎一致,整体加解密效果理想,可有效保障光学图像的安全性,而且本方法可以在最短3 s的时间内完成光学图像的加密和解密,加解密效率更高,综合效果更佳。

波前编码红外成像系统的温度梯度适应能力探究

利用波前编码技术为红外光学系统进行无热化设计可提高其在不同均匀工作温度下的适应能力,但针对温度突变、成像系统内温度分布不均情况,波前编码技术是否能正常进行成像及其适用的温度范围还有待进一步研究.为简化分析流程,采用温度梯度模型来仿真非稳态下的温度变化.利用温度梯度模型来定性分析光学系统在轴向、径向温度梯度为系统引入的附加像差.计算两个方向下的光程差变化来比较两种温度梯度环境下系统的成像性能差异.在此基础上,为非稳态温度环境下红外光学系统的设计建立了结合光/机/热分析的无热化设计流程,通过ZEMAX设计了一套最大轴向尺寸为85 mm、最大径向尺寸为25 mm的红外光学系统,通过SolidWorks加载轴向和径向的热形变,探究所设计的系统能够适用的温度梯度范围.结果表明,结合光/机/热分析的无热化设计流程可以有效表明系统在非稳态温度下的成像情况.对上述采用三次相位板进行无热化设计的红外光学系统,在非稳态温度下可以适应±10℃的轴向温差范围,但是仅可以适应±1℃的径向温差范围.因此在进行红外波前编码光学系统的无热化设计时,需要对径向方向进行重点优化.

基于数据隐私保护机制的光学图像加密研究

为提高光学图像信息的安全性,研究基于数据隐私保护机制的光学图像加密方法。采用Logistic映射的输出序列生成光学图像的混沌掩码,将其与螺旋相位掩码相结合,形成混合相位掩码,经希尔伯特变换和波带片相位模型调和后获取调和掩码,校正光学装置光轴;采用相位复用算法中的杨-顾算法,依据调和掩码将光学图像加密成实值光学图像,将线性滤波引入到解密光学图像中,提高解密光学图像质量与加密光学图像的数量,实现高容量的多光学图像加密。实验表明,该方法可压缩加密光学图像,并提高解密光学图像质量,加密质量系数为0.9,加密信息熵值平均为8.999 6。

基于离散奇里科夫混沌映射与分数阶随机变换的多图像加密算法

为了解决当前图像加密技术难以对多目标(≥3)同步置乱与扩散,增大了网络传输负载的不足,本文提出了离散奇里科夫混沌映射耦合分数阶随机变换的图像加密机制。基于奇里科夫标准映射,通过改变其混沌轨迹范围,提出了离散奇里科夫标混沌映射,根据初始条件,通过对其迭代,获取4个混沌序列,再基于引力模型,高度置乱输入明文的像素位置;随后,对任意两个置乱密文完成编码,输出纯相位掩码,并结合剩余的置乱图像,构成融合置乱图像;随后,通过迭代映射,将其输出的4个随机序列变成矩阵,构造相位掩码模型,形成4混沌掩码;最后,引入分数阶随机变换,设计像素扩散函数,完成多图像同步加密。测试结果显示:所提算法能够对多图像实现同步加密,具有较高的安全性与抗剪切攻击性能。

用于高速目标检测的相位编码信号处理方法和性能研究

波形选择是雷达系统设计的重要内容,在数字信号处理理论和计算平台的支持下,波形的处理转换为计算的问题,后端处理计算能力的提升极大地拓展了波形的应用场景。相位编码信号具有多普勒敏感特点,为实现匹配滤波,必须对目标可能出现的速度进行补偿,处理过程复杂,在多数雷达系统中应用场景有限。本文提出了相位解调+傅里叶变换构建滤波器组的方法完成相位编码信号的速度补偿,在单个脉冲内实现同时测距测速,针对空间目标的特点,分析了速度、加速度对波形参数的限制,仿真给出了目标遮蔽、处理损耗、测速精度的结果。

基于混沌与菲涅尔变换的多彩色图像加密算法

针对常见的基于混沌系统的多图像光学加密存在密钥敏感性不强、加密方法安全性不高等问题,设计了基于混沌Chen系统和菲涅尔变换的多彩色图像光学加密方法。首先,每幅彩色图像均被分解为R、G和B通道,并对每个通道的幅值独立进行归一化处理,得到归一化图像。其次,设定混沌系统初始值和控制参数,利用Chen混沌系统生成三个高维混沌相位掩码,分别对每幅图像的三通道相位信息进行调制处理,然后将调制后的R、G、B通道分别进行叠加重组。并对重组后的通道图像分别进行菲涅尔变换处理,得到相应的通道密文。最后,将通道密文重新融合,得到最终的密文图像。数值仿真结果表明,与现有的基于混沌系统的加密算法相比,所提算法具备更高的密钥敏感性,以及更高的抵抗各种攻击的能力,熵值达到了7.996,稳定的NPCR和UACI分别为99.84%、35.63%。

基于相位声码器的多轨个性化耳鸣掩蔽治疗声合成新方法

针对传统掩蔽治疗音在耳鸣声治疗中有效性和可听性不足的问题,本研究提出了一种基于相位声码器(phase vocoder,PV)和渐变混合算法的个性化多轨耳鸣掩蔽治疗音(multi-track personalized tinnitus masking therapy sound,MT-PTMTS)合成方法。本研究以生物自然音库和环境背景自然音库为基础,利用PV进行音调变换,同时使用迭代函数系统(iterated function system,IFS)分形映射算法合成能够匹配患者耳鸣频段的时长可控且相似不重复的个性化生物自然音,并加入经渐变混合算法拼接而成的环境背景自然音。实验结果表明,本研究合成的治疗音在频段上可有效匹配患者的耳鸣频段,且符合1/f波动;此外,治疗音输入耳鸣模型能有效抑制对应频段耳鸣。试听结果表明,治疗音怡人且自然,对耳鸣声治疗具有一定的参考价值。

扩大光学系统焦深范围的光学成象新技术研究

如何增大非相干光学系统的焦深已成为一项有意义的研究主题 .对于普通光学系统 ,其焦深与光学系统的相对孔径平方成反比 .为了增大焦深 ,通常的做法是缩小相对孔径 ,但这种做法有其缺点 :会降低光学系统的光通量及调制传递函数 (MTF)和分辨率 .本文提出了一种新方法 ,通过在光学系统光路中加入一特殊设计的非球面掩模板 ,并用图象处理技术对相位掩模板编码后的图象进行解码得到清晰图象 .保证了光学系统在维持原有相对孔径的同时扩大其焦深范围 。

一种基于OTF稳定性的波前编码相位板优化方法

提出了一种简单的可用于光学系统中子午弧矢方向白光OTF稳定性评价的波前编码相位板参量优化方法.该方法仅以标准偏差来评价OTF在目标景深范围内的稳定性,并且结合自适应模拟退火算法在参量空间内优化得到相位板的最佳参量.使用该方法优化得到的相位板参量,可以大幅度提高光学系统的景深,并且可以获得更为清晰、稳定的成像.对应用波前编码技术前后光学系统的成像性能作了比较,并且考察了优化参量的容差性.