分析组合型余弦光栅的衍射场

为了研究组合型余弦光栅的衍射场,采用波前相因子判断法并考虑到光栅孔径的影响,得到了组合型余弦光栅的衍射场所含基元成分,导出像面上的衍射场振幅分布公式,并数值模拟了像面上衍射场振幅分布和光强分布,最后得出各焦斑的半角宽度。结果表明,该研究可为余弦光栅用于滤波和光学信息处理技术提供一个理论基础。     

三维物场多重分数傅里叶变换全息图光电再现实验研究

对基于多重分数傅里叶变换(FrFT)的三维(3D)物场计算全息图进行光电再现实验研究.根据分数阶与衍射距离的关系,对不同物面分别设置不同的分数阶,分别计算得到各层物面在全息面的复振幅并进行叠加,对其进行编码分别得到分数傅里叶变换振幅型全息图和相息图.同时在计算3D物场的全息图时,在物波面加入不同的随机相位因子,得到3D...     

布拉格声光衍射场光强空间分布不均匀的研究

从波动方程出发,结合声光移频器的工作原理,根据声光晶体的有限尺寸,建立声场模型,推导出布拉格声光作用的耦合波方程。有限差分方法分析衍射场光强的空间三维分布。结果表明,声场振幅的不均匀分布会影响声光衍射场的光强分布。     

一种无轮廓像干扰光学加密系统

将光学中的干涉与衍射原理相结合,提出了一种新的光学加密系统。该光学加密系统将图像信息隐藏于两个相位板(POM)及一个振幅板(AOM)中,其中振幅板使用计算机随机生成,两个相位板则通过解析方法得到。解密时,使用相干光照射两个相位板,并通过分束镜使二者的衍射光场进行相干叠加,此干涉场被振幅板调制,再经衍射一段距离后所得衍射场强度即为原始图像,此图像可以采用CCD等图像传感器件直接记录。本方法不但消除了先前提出的基于干涉原理加密方法存在的"轮廓像"问题,也对部分密钥泄露攻击具有很强的稳健性,具有较高的安全性。此外,本方法原理简单,加密过程无需迭代,解密系统易于物理实现。计算机模拟结果证实了本方法的有效性。     

二元光学元件各级光强的分布规律和衍射效率

用振幅矢量作图法研究二元位相元件各级衍射光强的分布规律．并得出了普遍的衍射效率公式，方法简便，物理图像清晰，结果普遍适用。     

一维周期光栅的菲涅耳衍射研究及光栅常数的测试

基于标量衍射理论研究一维周期振幅型光栅在不同照明条件下的光波场分布,理论上获得了平面波和球面波照明条件下的菲涅耳衍射场的分布特征,并给出实验证明。根据研究结果,提出一种测量光栅常数的方法,并将该方法与用分光计测量的结果进行比较。通过实验证实了所提出方法的可行性。     

部分相干光束经刀边衍射产生的光谱变化

从部分相干光束的传输定律出发,得到了部分相干光束刀边衍射时的远场光谱的表达式．根据该表达式对衍射场中的光谱进行了理论研究。研究的结果表明：衍射场中的光谱将随着观察点位置而改变,并且对于固定观察点,其光谱将随着相对空间相干度以及光束透过率的变化而变化。     

双腔光力学系统中斯托克斯场与反斯托克斯场性质的研究

正主要研究双腔光力学系统中弱探测场的斯托克斯场与反斯托克斯场的非线性性质.在这个系统中,力学振子与左右两侧控制场耦合并产生光压项,正是由于这种非线性光压项的作用,使得左右两侧的控制场振幅和频率对探测场的斯托克斯和反斯托克斯过程产生了显著的影响.通过考虑系统与环境之间的相互作用,引入了相应物理量的耗散项,然后再由系统的哈密顿量得到系统的郎之万-海森堡方程组.其次,由于探测场场强远远小于控制场的场强,所以通过微扰论对系统的郎之万-海森堡方程组进行求解.取—级近似之后得到了探测场的斯托克斯场与反斯托克斯场的振幅,最后通过数值分析研究发现,当左右两侧控制场频率均在力学红边带下(红失谐),左右两侧控制场的振幅比值大小对探侧场的吸收强弱影响很大,特别是当左右两侧控制场的振幅比值为1时,斯托克斯场的输出功率基本为零.当振幅比值(右边控制场振幅比左边控制场振幅)由1不断增大时,斯托克斯场的输出功率会由零不断增大,SP斯托克斯场吸收深度不断变浅,而反斯托克斯场的输出功率会有所减少?当右侧控制场振幅增大到左侧控制场振椹的1.73倍时,斯托克斯场吸收深度大约为振椹比值为1时吸收深度的75%.而当关闭右侧控制场(振幅比值为0)并且左侧控制场频率依然在力学红边带下’斯托克斯场输出功率将会出现增益,反斯托克斯场的输出功率也会有所增加.所以在左右两侧控制场频率均在力学红边带下,通过控制左右控制场的振幅比可以非常有效地控制,斯场与反斯托克斯场输出功率大小?由此可知,对双腔光力学系统中斯托克斯场和反斯托克斯场的研究不但为研究光力学相互作用非线性性质提供一个非常重要的手段,同时也为实现量子通信中的全光开关提供了一个新的途径。     

用三区振幅和相位滤波器优化固体浸没透镜显微系统的光场分布

构造了三区振幅型和相位型滤波器,用矢量衍射理论分析了两种滤波器对固体浸没透镜显微系统透射场的优化作用.从光斑大小、聚焦强度(Strehl比)和边瓣强度等方面比较了两种滤波器的超分辨特性.数值结果指出,振幅型滤波器具有边瓣强度小,边界参数容限大的优点.相位型滤波器的超分辨效果比振幅滤波器的好,它的聚焦强度比振幅型的大.但是它的边瓣强度比振幅型的大.     

正交余弦光栅的衍射场

为了研究正交余弦光栅的衍射场,采用波前相因子判断法并考虑到光栅孔径的影响,对正交余弦光栅的衍射进行了理论分析,得到了正交余弦光栅衍射场所含基元成分,导出了像面波前函数、像面振幅分布函数和光强分布函数,并得出主焦斑的半角宽度.结果表明,该研究可为光栅用于光学信息处理技术提供理论依据.     

A new 2-D model for operating point shift in large LWIR HgCdTeFPA's

Infrared focal plane arrays (IRFPAs) are rapidly increasing in size. It is shown here that for large FPAs a considerable shift in the operating point occurs, which, if not reduced, introduces unacceptably large nonuniformity in the array response. This shift results because of the variable voltage drop across the HgCdTe active layer, due to its finite distributed resistance. A new analytical two-dimensional (2-D) model to estimate the operating point shift of individual detectors of long wavelength infrared (LWIR) HgCdTe focal plane array (FPA) is presented. Avoiding this operating point shift requires an optimized grid pattern     

中红外硅微透镜阵列的离焦效应

本文采用严格数值算法对中红外硅微透镜阵列进行了模拟,该微透镜阵列特征尺寸小于波长工作波长。研究发现该微透镜阵列存在一个显著的离焦效应,其离焦量达到0.4左右,超出了现有的传统理论模型预测范围。对微透镜阵列进行了制作和焦距测试,发现测试结果跟数值模拟基本吻合。微纳衍射光学集成系统中透镜离焦量是系统集成非常重要的一个参数,该研究结果为硅微透镜阵列和中红外探测器光学集成提供有效参考。     

COS光束和焦移的特性分析

本文分析讨论了ＣＯＳ光束的焦移特性，研究了影响焦移的因素，定义了焦移存在性判据。     

Sequences achieving the boundary of the entropy region for a two-source are virtually memoryless (Corresp.)

For a joint distribution{rm dist}(X,Y), the functionT(t)=min { H(Y|U): I(U wedge Y|X)=O, H(X|U)geq t}is an important characteristic. It equals the asymptotic minimum of(1/n)H(Y^{n})for random pairs of sequences(X^{n}, Y^{n}), wherefrac{1}{n} sum ^{n}_{i=1}{rm dist} X_{i} sim {rm dist} X, {rm dist} Y^{n}|X^{n} = ({rm dist} Y|X)^{n}, frac{1}{n}H(X^{n})geq t.We show that if, for(X^{n}, Y^{n})as given, the rate pair[(1/n)H(X^{n}),(1/n)H(Y^{n})]approaches the nonlinear part of the curve(t,T(t)), then the sequenceX^{n}is virtually memoryless. Using this, we determine some extremal sections of the rate region of entropy characterization problems and find a nontrivial invariant for weak asymptotic isomorphy of discrete memoryless correlated sources.     

Focal shift and focal switch of flattened Gaussian beams in passage through an aperture bifocal lens

A detailed study of the focal shift and accompanying focal switch of flattened Gaussian beams (FGBs) passing through an aperture bifocal lens is presented. It is shown that by suitably choosing the parameters of the optical system and beam, there exists two axial irradiance maxima for focused FGBs, which vary with the Fresnel number of the aperture. The focal switch can take place when the Fresnel number decreases gradually. The focal switch of Gaussian beams is treated as a special case of FGBs. From the axial irradiance distribution of focused FGBs, a physical explanation of the focal switch is given. A comparison with previous work is also made.     

An achievable rate region for the multiple-access channel with feedback

An achievable rate regionR_{1} leq I(X_{1};Y|X_{2},U), R_{2} leq I(X_{2}; Y|X_{1},U), R_{1}+R_{2} leq I(X_{1}, X_{2};Y), wherep(u,x_{l},x_{2},y)= p(u)p(x_{l}|u)p(x_{2}|u)p(y|x_{l},x_{2}), is established for the multiple-access channel with feedback. Time sharing of these achievable rates yields the rate region of this paper. This region generally exceeds the achievable rate region without feedback and exceeds the rate point found by Gaarder and Wolf for the binary erasure multiple-access channel with feedback. The presence of feedback allows the independent transmitters to understand each other's intended transmissions before the receiver has sufficient information to achieve the desired decoding. This allows the transmitters to cooperate in the transmission of information that resolves the residual uncertainty of the receiver. At the same time, independent information from the transmitters is superimposed on the cooperative correction information. The proof involves list codes and block Markov encoding.     

聚焦异常空心光束的焦移

基于柯林斯衍射积分公式推导出了异常空心光束通过薄透镜聚焦后的解析表达式。运用导出公式,通过数值计算分析了异常空心光束聚焦区域的光强分布,并对异常空心光束的焦移特性进行了研究,详细讨论了光束有效菲涅耳数、光束形状和光腰位置对焦移的影响。研究结果表明:聚焦异常空心光束的轴上光强最大点不与几何焦点重合,而是偏离几何焦点。通过选择合适的光束参数和光学系统,异常空心光束将发生异常空心光束的焦移,其焦移量不仅依赖于光束有效菲涅耳数,而且依赖于光束椭圆率以及光束入射面与透镜的距离。     

Effect of Nitrogen on the Frequency Dependence of Dynamic NBTI-Induced Threshold-Voltage Shift of the Ultrathin Oxynitride Gate P-MOSFET

The dynamic negative-bias-temperature-instability- induced threshold-voltage shift |DeltaV_t| of p-MOSFETs employing ultrathin decoupled-plasma- and thermal-nitrided SiO₂ gate dielectrics is studied as a function of gate frequency. The dependence of |DeltaV_t| on the gate frequency under unipolar stress is observed to become weaker for p-MOSFETs having higher nitrogen concentrations in the gate oxide. Evidence shows that reduced frequency dependence results from a greater lock-in of |DeltaV_t|, mainly due to an increased generation of recovery-resistant deep-level hole traps in the heavily nitrided gate p-MOSFET.     

Distortionless vestigial-sideband transmission with symmetric delay about the carrier frequency and synchronous demodulation

The general amplitude condition is (MU ? ML)2 + MU ML/MO2 = 1. where MU and ML are upper and lower sideband amplitudes and MO ? ? is arbitrary. The demodulating carrier phase ? is determined from MO cos (?+?) = ?, where ?O is the phase shift at the carrier. The delay condition is ?U = ?L? = T±(MU ML? + MU? ML) MO?1|sin (?+?O)|, where ?U? and ?L? are upper and lower sideband delays and T is an arbitrary constant. The value MO = ? gives the well known `constant-sideband-sum? condition and MO = 1/?2 the recently discovered `constant-sideband-squared-sum? condition.     

Performance of 1REC-MHPM in the presence of adjacent channelinterference

The effect of adjacent channel interference (ACI) on the error probability of the rectangular frequency pulse multi-h phase-coded modulation (1REC-MHPM) is studied. Evaluations through simulation were done for different values of the absolute adjacent channel frequency spacing |Δf|, different time delay τ between the main channel and the interfering channel, and schemes with different number of modulation indexes. It is found that ACI effects can only be eliminated when |Δf| approaches 2.0. Comparison with minimum shift keying (MSK) is also made through simulation