二元纯位相片实现半导体激光器到单模光纤的耦合

采用二元光学位相调制的基本思想，用二元纯位相型光学系统将椭圆高斯型激光束与单模光了佳耦合。采用两块纯 位相片来进行波前变换，将椭圆型高斯激光束转变成对称圆高斯激光束，并与单我纤的基模最佳匹配耦合。     

Convergence of cascade algorithm for individual initial function and arbitrary refinement masks

The cascade algorithm plays an important role in computer graphics and wavelet analysis. For any initial function φn, a cascade sequence (φn)n∞=1 constructed by the iteration φn=Cnφn-1=1,2.. where Cαis defined by g∈Lp(R) In this paper, we characterize the convergence of a cascade sequence in terms of a sequence of functions and in terms of joint spectral radius. As a consequence, it is proved that any convergent cascade sequence has a convergence rate of geometry, i.e., ||φ 1-φn||Lp(R)=O((？)n)for some (？)∈(0.1i). The condition of sum rules for the mask is not required. Finally, an example is presented to illustrate our theory.     

Study of Serrated Aperture for a Cassegrain Booster Amplifier

The upgrade of the actual large laser facilities (GEKKO XII in our case) implies an increase of filling-factor, but avoiding the generation of spatial high frequencies. To reach that purpose we intend to construct the beams using serrated apertures with an optimised shape. The performances of our system led after simulation to a 70% filling factor with less than 2% fluctuation on the laser pattern intensity map. The optimisation was also checked from a financial point of view. The usual serrated apertures are already giving good results, so we attached ourselves to seek for financial efficiency.     

Subdivision Schemes and Refinement Equations with Nonnegative Masks

We consider the two-scale refinement equation f(x)=∑^N_n=0 c_nf(2x−n) with ∑_n c_2n=∑_n c_2n+1=1 where c₀, c_N≠0 and the corresponding subdivision scheme. We study the convergence of the subdivision scheme and the cascade algorithm when all c_n0. It has long been conjectured that under such an assumption the subdivision algorithm converge, and the cascade algorithm converge uniformly to a continuous function, if and only if only if 0<c₀, c_N<1 and the greatest common divisor of S={n: c_n>0} is 1. We prove the conjecture for a large class of refinement equations.     

微型太阳敏感器光学掩模的镀膜设计

太阳敏感器是空间飞行器进行姿态确定和方位测定的重要器件，传统太阳敏感器大而重，无法应用到微小卫星特别是皮纳卫星上。介绍了基于CMOS APS探测器的微型太阳敏感器的工作原理，基于黑体辐射理论和太阳光谱特性，结合CMOS APS探测器工作特性，分析给出了这种敏感器像元表面产生光电子数的计算方法，并采用Matlab软件，编程计算了地球表面太阳垂直入射条件下，探测器像元表面产生的光电子数。采用光学薄膜设计方法，分析设计了掩模表面光学薄膜的膜系结构，计算了各膜层的透射特性。在此基础上，得到了基于CMOS APS探测器微型太阳敏感器光学掩模的光学薄膜的设计方法，最后给出了设计结果。     

Optimized phase pupil masks for extended depth of field

By properly designing a phase pupil mask to modulate or encode the optical images and then digitally restoring them, one can greatly extend the depth of field and improve image quality. The original works done by Dowski and Cathey introduce the use of a cubic phase pupil mask to extend the depth of field. The theoretical and experimental researches all verified its effectiveness. In this paper, we suggest the use of an exponential phase pupil mask to extend the depth of field. This phase mask has two variable parameters for designing to control the shape of the mask so as to modulate the wave-front more flexible. We employ an optimization procedure based on the Fisher information metric to obtain the optimum values of the parameters for the exponential and the cubic masks, respectively. A series of performance comparisons between these two optimized phase masks in extending the depth of field are then done. The results show that the exponential phase mask provide slight advantage to the cubic one in several aspects.     

口罩中的化学与技术*

以医用外科口罩、新型纳米口罩等为例,分析了口罩的组成材料、加工技术及防护原理,对于公众了解口罩的材料组成、性能、科学选用之间的关系,提高科学素养和公共健康安全意识有积极作用。     

波前编码双共轭梯度平方稳定解码算法及其 TMS320DM642平台的实现

波前编码是一种新型的光学-数字混合二步成像系统,采用三次光学编码相位板可以得到系统的非对称点扩散函数和相当景深内模糊程度一致的中间图像.本文利用空间域光学成像模型,结合反镜像边界束缚条件以及矩阵的直积分解,提出一种基于双共轭梯度平方稳定算法(Bi-CGSTAB)的图像复原算法实现波前编码系统的数字解码.该算法具有计算量小、计算速度快,几乎没有边界效应等优点.在此基础上结合TMS320DM642平台并行计算的特点,将新的算法重新优化并移植到TMS320DM642平台上.整个平台由图像采集模块、图象显示模块以及外部存储器等模块组成.通过专门设计的光学系统,分别对物距为1m、5m和10m处的物体以及人像进行成像.对中间模糊像的恢复实验结果表明,新的算法在TMS320DM642平台上图像复原速度快,效果好,为波前编码系统的真正便携和实用提供了可能.     

基于45°倾斜光纤光栅的线偏振输出掺镱光纤激光器

对工作于1 064nm波段的45°倾斜光纤光栅的偏振依赖损耗特性与工作机理进行了分析.利用紫外曝光法,将周期为1 070nm的常规相位模板旋转33°后,在光敏光纤上写制了45°倾斜光纤光栅,写制的光栅栅区长度为12mm,在1 040~1 085nm范围内偏振依赖损耗值为7dB左右.影响其偏振依赖损耗值的主要原因为相位模板的周期不是最佳值和栅区长度不够.利用写制的45°倾斜光纤光栅作为起偏器件,实现了线偏振输出的掺镱光纤激光器,其激光消光比高于30dB,输出波长为1 065.4nm,3dB线宽为0.08nm,最高输出功率8.7mW,可长时间保持高偏振度稳定工作.     

Synchronization of spatiotemporal semiconductor lasers and its application in color image encryption

Optical chaos is a topic of current research characterized by high-dimensional nonlinearity which is attributed to the delay-induced dynamics, high bandwidth and easy modular implementation of optical feedback. In light of these facts, which add enough confusion and diffusion properties for secure communications, we explore the synchronization phenomena in spatiotemporal semiconductor laser systems. The novel system is used in a two-phase colored image encryption process. The high-dimensional chaotic attractor generated by the system produces a completely randomized chaotic time series, which is ideal in the secure encoding of messages. The scheme thus illustrated is a two-phase encryption method, which provides sufficiently high confusion and diffusion properties of chaotic cryptosystem employed with unique data sets of processed chaotic sequences. In this novel method of cryptography, the chaotic phase masks are represented as images using the chaotic sequences as the elements of the image. The scheme drastically permutes the positions of the picture elements. The next additional layer of security further alters the statistical information of the original image to a great extent along the three-color planes. The intermediate results during encryption demonstrate the infeasibility for an unauthorized user to decipher the cipher image. Exhaustive statistical tests conducted validate that the scheme is robust against noise and resistant to common attacks due to the double shield of encryption and the infinite dimensionality of the relevant system of partial differential equations.