大气湍流中部分相干光束上行和下行传输偏振特性的比较

以部分相干的电磁高斯-谢尔模型(electromagnetic Gaussian-Schell model, EGSM) 光束为研究对象, 根据相干和偏振的统一理论以及随机光束的Stokes参量, 推导出EGSM光束在大气湍流中斜程传输时的偏振度(degree of polarization, DoP)和偏振方向角的表达式, 研究了大气湍流中上行和下行传输时EGSM光束偏振特性的不同. 研究结果表明: 在相同条件下, EGSM 光束下行传输时整个光场DoP的分布比上行传输要集中; 下行传输时轴上点的DoP达到最大值所对应的传输距离长于上行传输. 可以看出, EGSM光束沿下行路径传输时, 探测器可以接收更远距离处的波束传输信息.     

Evolution of the degree of polarization of an electromagnetic Gaussian Schell-model beam in a Gaussian cavity

The interaction of an electromagnetic Gaussian Schell-model (EGSM) beam with a Gaussian cavity is analyzed. In particular, the evolution of the degree of polarization of the EGSM beam is investigated. The results show that the behavior of the degree of polarization depends on both the statistical properties of the source that generates the EGSM beam and the parameters of the cavity.     

Twist phase-induced polarization changes in electromagnetic Gaussian Schell-model beams

Electromagnetic Gaussian Schell-model (EGSM) beam with twist phase (i.e., twisted EGSM beam) is introduced as an extension of its scalar version based on the unified theory of coherence and polarization. We show how analytical paraxial propagation formulae of isotropic and anisotropic EGSM beams passing through a general astigmatic ABCD optical system can be modified in the presence of the twist phase. Numerical examples demonstrate that the twist phase affects the spectral density, the state of coherence, and the degree of polarization of EGSM beams on propagation.     

Degree of paraxiality of a stochastic electromagnetic Gaussian Schell-model beam

The concept of the degree of paraxiality introduced recently for monochromatic fields is extended to the domain of stochastic electromagnetic fields. Analytical expression for the degree of paraxiality of a stochastic electromagnetic Gaussian Schell-model (EGSM) beam is derived. Numerical results show that the degree of paraxiality of an EGSM beam is determined by the degree of polarization, r.m.s. widths of the spectral densities and of the correlation functions of its source. Degree of paraxiality of an EGSM beam after passing through a linear polarizer is also analyzed. Our results show that one can modulate the degree of paraxiality of an EGSM beam by a linear polarizer.     

Coincidence fractional Fourier transform with a stochastic electromagnetic Gaussian Schell-model beam

Based on classical theory of optical coherence and polarization, coincidence fractional Fourier transform (FRT) with a stochastic electromagnetic Gaussian Schell-model (EGSM) beam is investigated. Dependences of the quality and visibility of the coincidence FRT pattern of an object on the degree of polarization and correlation coefficients of the EGSM beam are studied numerically. It is shown that the quality and visibility of the coincidence FRT pattern of an object are determined by the polarization and coherence of the EGSM beam together.     

Thermal-lens effect induced changes of polarization, coherence and spectrum of a stochastic electromagnetic beam in a Gaussian cavity

Based on the unified theory of coherence and polarization, the interaction of a stochastic electromagnetic Gaussian Schell-model (EGSM) beam with a Gaussian cavity containing thermal-lens medium is analyzed. In particular, the effect of the thermal medium of the lens on the evolution properties of the degree of polarization, the degree of coherence and the spectral shift are investigated in detail. It is shown that the thermal-lens medium has a strong influence on the behavior of the EGSM beam especially in unstable resonators, thus it is necessary for us to take the thermal-lens effect into consideration in practice.     

大气湍流对部分相干电磁平顶光束传输的影响

基于相干性和偏振性统一理论,采用Rytov相位结构函数平方近似推导出了部分相干电磁平顶光束在湍流大气中传输的偏振度、相干度和光谱强度公式,并研究了湍流对其传输特性的影响.研究表明,偏振度和相干度与源光谱的带宽无关.大气湍流使得不同阶数的部分相干电磁平顶光束的偏振度经长程传输后均趋于其初始值.大气湍流使得部分相干电磁平顶光束与电磁高斯-谢尔模型光束相干度的差别减小,并导致相干度的振荡和相位奇异现象消失.大气湍流使得相干性较好的部分相干电磁平顶光束的光谱跃变现象消失.     

大气湍流对部分相干电磁平顶光束传输的影响

基于相干性和偏振性统一理论,采用Rytov相位结构函数平方近似推导出了部分相干电磁平顶光束在湍流大气中传输的偏振度、相干度和光谱强度公式,并研究了湍流对其传输特性的影响.研究表明,偏振度和相干度与源光谱的带宽无关.大气湍流使得不同阶数的部分相干电磁平顶光束的偏振度经长程传输后均趋于其初始值.大气湍流使得部分相干电磁平顶光束与电磁高斯一谢尔模型光束相干度的差别减小,并导致相干度的振荡和相位奇异现象消失.大气湍流使得相干性较好的部分相干电磁平顸光束的光谱跃变现象消失.     

Spectral shift of a stochastic electromagnetic Gaussian Schell-model beam in a Gaussian cavity

Spectral changes of a stochastic electromagnetic Gaussian Schell-model (EGSM) beam interacting with a Gaussian cavity are investigated. It is shown that the spectral shift is mainly determined by the degree of polarization of the initial beam and by the parameters of the cavity. Generically the blue shift occurs at on-axis points, while the red shift can occur at off-axis points. The condition under which the relative spectral shift is independent of the degree of polarization of the initial beam is analyzed.     

M2-factor of a truncated electromagnetic Gaussian Schell-model beam

Based on the extended Huygens–Fresnel integral and the second-order moments of the Wigner distribution function, analytical expression for the M ²-factor of a truncated electromagnetic Gaussian Schell-model (EGSM) beam in turbulent atmosphere is derived by expanding the hard-aperture function into a finite sum of complex Gaussian functions. It is found that the evolution properties of the normalized M ²-factor of a truncated EGSM beam are closely determined by the truncation parameter, the parameters of the source beam and the parameters of the turbulent atmosphere together. The advantage of the EGSM beam for overcoming the turbulence-induced degradation disappears gradually as the truncation parameter decreases.     

The statistical properties of anisotropic electromagnetic beams passing through the biological tissues

We report the analytic formula of an electromagnetic Gaussian–Schell-model (EGSM) beam propagating through the turbulent biological tissues. With the help of this formula, the changes in characteristics of the beam such as the spectral density, the spectral degree of coherence, the spectral degree of polarization, and the spectral degree of cross-polarization of the EGSM beam passing through the biological tissues are illustrated and compared by numerical examples. The changes in anisotropic and isotropic EGSM beams are indicated. Necessary comparisons and analyses of the beams generated by the anisotropic source and the isotropic source through the turbulent biological tissues are given. Moreover, the influence of the light source and turbulence of tissues on the changes of the spectral degree of cross-polarization of the EGSM beam passing through the biological tissues are compared in the near-field and the far-field.     

Changes in the coherence of quasi-monochromatic electromagnetic Gaussian Schell-model beams propagating through turbulent atmosphere

Based on the extended Huygens-Fresnel principle, the mutual coherence function of quasi-monochromatic electromagnetic Gaussian Schell-model (EGSM) beams propagating through turbulent atmosphere is derived analytically. By employing the lateral and the longitudinal coherence length of EGSM beams to characterize the spatial and the temporal coherence of the beams, the behavior of changes in the spatial and the temporal coherence of those beams is studied. The results show that with a fixed set of beam parameters and under particular atmospheric turbulence model, the lateral coherence of an EGSM beam reaches its maximum value as the beam propagates a certain distance in the turbulent atmosphere, then it begins degrading and keeps decreasing along with the further distance. However, the longitudinal coherence length of an EGSM beam keeps unchanging in this propagation. Lastly, a qualitative explanation is given to these results.     

部分相干平顶光束经光阑衍射的偏振特性

根据光束的相干-偏振矩阵和传输理论,对部分相干平顶光束经正多边形光阑衍射的偏振特性进行了系统的研究.给出了部分相干平顶光束偏振度传输公式,并将高斯-谢尔模型光束以及部分相干平顶光束在自由空间传输的偏振度作为特例统一于一般表达式中.研究表明：部分相干平顶光束经光阑衍射的偏振特性与光阑截断参数、光束的空间相干性、衍射角、传输距离、平顶光束的阶数有关. 关键词： 部分相干平顶光束 偏振特性 相干-偏振矩阵 正多边形光阑 光阑衍射     

部分相干平顶光束经光阑衍射的偏振特性

根据光束的相干-偏振矩阵和传输理论，对部分相干平顶光束经正多边形光阑衍射的偏振特性进行了系统的研究.给出了部分相干平顶光束偏振度传输公式，并将高斯-谢尔模型光束以及部分相干平顶光束在自由空间传输的偏振度作为特例统一于一般表达式中.研究表明：部分相干平顶光束经光阑衍射的偏振特性与光阑截断参数、光束的空间相干性、衍射角、传输距离、平顶光束的阶数有关.     

在一种新的聚合物材料上刻写正弦相位波导光栅及其特性研究

用双光束干涉法在一种新的聚合物材料IAC-4上刻写正弦相位型光栅,实现了光栅耦合光波导,并研究了该光波导对不同偏振态的入射光的传播特性,对光栅的形成进行了理论分析,对光波导的传播常数进行了数值计算,并对该波导光栅在导光的光强调制和方向控制及其在集成光学方面的应用进行了讨论,最后对任意入射角的光栅方程进行了理论探讨. 关键词： 波导光栅 有机聚合物 平板光波导 集成光学     

Quantum polarization fluctuations of partially coherent dark hollow beams in non-Kolmogorov turbulence atmosphere

Non-classical polarization properties of dark hollow beams propagating through non-Kolmogorov turbulence are studied. The analytic equation for the polarization degree of the quantization partially coherent dark hollow beams is obtained.It is found that the polarization fluctuations of the quantization partially coherent dark hollow beams are dependent on the turbulence factors and beam parameters with the detection photon numbers. Furthermore, an investigation of the changes in the on-axis propagation point and off-axis propagation point shows that the polarization degree of the quantization partially coherent dark hollow beams presents oscillation for a short propagation distance and gradually returns to zero for a sufficiently long distance.     

Real-time analysis of partially polarized light with a space-variant subwavelength dielectric grating

A novel method for real-time polarization measurement is presented. The method is based on a space-variant wave plate that we realized as a computer-generated space-variant subwavelength dielectric grating. The Stokes parameters of the incident beam are determined by Fourier analysis of the space-variant intensity transmitted through the grating and an analyzer. We discuss the design and realization of such wave plates and demonstrate our technique with polarization measurements of both polarized and partially polarized CO(2)-laser radiation at a wavelength of 10.6 mum.     

Stokes beams formed by superposition of a completely unpolarized and a completely polarized Gaussian Schell-model beam

Analytic expressions and computed examples are given to elucidate the coherence and polarization properties of Stokes beams, i.e. beams formed by superposition of a completely unpolarized and a completely polarized electromagnetic Gaussian Schell-model beam. We found that superposition of such two beams cannot form a Stokes beam with a constant state of polarization on propagation. An additional constraint on the source plane parameters of the two Gaussian Schell-model beams is proposed. The resultant Stokes beam with a constant state of polarization on propagation is found to be a Gaussian Schell-model beam with the same variances as the two constituent Gaussian Schell-model beams. However, the modulus of the Gaussian intensity distributions across the source planes of these beams may be different.     

线偏振高斯光束通过条形浮雕光栅的传输

使用角谱表示和严格的模式理论研究了线偏振高斯光束通过特征尺寸与波长可比拟的条形浮雕光栅的传输，系统参数误差对浮雕层中光强最大值的影响.研究表明，光束在条形浮雕光栅各层中有不同的光强分布，浮雕层的介质填充部分中的光强明显高于展空部分的光强.光栅周期误差对浮雕层中最大光强的影响起主要作用.并利用模拟退火优化算法优化系统参数以控制出射光束的光强分布.     

Changes in polarization of Gaussian Schell-model beams and partially polarized Gaussian Schell-model beams through a polarization grating

The polarization properties of Gaussian Schell-model (GSM) beams and partially polarized Gaussian Schell-model (PGSM) beams passing through a polarization grating (PG) are studied based on the beam coherence-polarization (BCP) matrix formulism, where the finite size of the PG is considered. Detailed numerical calculation results are given and compared with the previous work.