非线性管理光纤光栅中的调制不稳定性研究

基于非线性耦合模方程,研究了非线性管理光纤光栅中的调制不稳定性,得到了调制不稳定性的色散关系。与常规的非线性光纤光栅相比,在非线性管理光纤光栅中,克尔非线性的变化改变了调制不稳定性增益谱的谱宽和幅度,并导致新的不稳定性区域的出现:在反常色散区,原来关于零波数对称的两个旁瓣随着克尔非线性变化的增加其增益幅度递减至零,在经历了一段无增益区域之后,又逐渐形成了在零波数附近区域的一个新的单峰;而在正常色散区,除了原来的两个增益区域之外,零波数附近出现了新的增益区,增益的幅度随克尔非线性变化的增加而递增。可见,非线性管理光纤光栅给调制不稳定性的产生提供了更多的空间。     

激光原位角膜磨镶手术后不良症状的光学分析

测量了准分子激光原位角膜磨镶(LASIK)手术后人眼的单色像差。并根据术后症状,将所有数据分类为视物星芒状组、单眼复视组、视物雾状组和参考组。视物星芒状组和视物雾状组的三阶和四阶泽尼克(Zernike)像差的均方根(RMS)值明显大于无症状的参考组。术后有不良症状各组的人眼的调制传递函数(MTF)明显低于参考组的调制传递函数。在明视觉条件下,四阶像差特别是对称性的泽尼克球差,对调制传递函数的影响大;而在暗视觉条件下,三阶像差特别是非对称性的泽尼克彗差对调制传递函数的影响大。四阶以上的高阶像差对各有症状组的调制传递函数曲线有影响,而这些高阶像差对参考组的调制传递函数已无明显影响。像差的均方根值和调制传递函数曲线是研究术后不良症状的较有效光学手段。     

Interference suppression algorithm based R-TDD for multi-user MIMO heterogeneous network

Aiming at the problem of uplink co-channel interference in multi-user multi-input multi-output (MIMO) heterogeneous network, a reversed time division duplex (R-TDD)-based method is used to improve the performance of interference rejection combining (IRC) algorithm. This method overcomes the difficulty of IRC algorithm in obtaining the interference noise covariance matrix by utilizing the R-TDD transmission scheme. On the premise that the spectrum efficiency is guaranteed, through combining R-TDD with spatial modulation, the transmission complexity is significantly reduced and the uplink co-channel interference is effectively controlled, so as to improve the system performance. Simulation results demonstrate that the R-TDD-based scheme can improve the performance of IRC algorithm in terms of spectrum efficiency.     

Numerical simulations to improve the performance of tunable diode laser absorption tomography in a harsh combustion environment

The impact of measurement noise and tomographic methods on reconstruction quality are investigated via simulation studies under a hypothesis harsh flow field environment. Computer tomographic methods based on direct absorption spectroscopy and wavelength modulation spectroscopy are conducted under different measurement noise levels to assess the noise effect quantitatively. It turns out that the wavelength modulation spectroscopy-based tomographic method shows efficient immunity to measurement noise. However, the direct absorption spectroscopy-based tomographic method is found to be susceptible to the measurement noise, which makes the reconstruction quality decline with the increasing noise level. In addition, two kinds of tomographic methods including linear and nonlinear method are investigated under a complex multimodal temperature distribution environment with limited projection data. The reconstructed distribution for the nonlinear tomographic method reveals great fidelity to the original value with a maximum deviation of 51.9?K, while the reconstructed distribution for the linear tomographic method under parallel beam arrangement shows an obvious distortion.     

Effect of the Time-Dependent Atom-Field Couplings on Entanglement

A model containing two two-level atoms and a single-mode cavity is considered, and the effect of the time-dependent atom-field couplings on entanglement between the two atoms is studied. The results indicate that both for one-photon processes and for two-photon processes, the disappearance of the initial entanglement is delayed due to the linear modulation of the atom-field coupling coefficients as compared to the constant coupling model. The delayed time of the disappearance of the initial entanglement for the two-photon processes is much longer than that for the one-photon processes in the case of adiabatic variation.     

单模CO2激光器动力学参数的实验研究

给出以失谐量对输出的影响来独立测定单模ＣＯ２激光器有关动力学参数的方法及所得结果。     

折反射物镜系统光圈的计算与分析

讨论光圈的分配与给定,并以折反射光学系统为例进行分析和计算。     

Design considerations for a fibre-optic based polarimeter

A polarization modulation technique is presented which utilizes the manipulation of a wide band, incoherent source. An application to the measurement of sugar concentration is described. A conceptual fibre-optic sensor, based on the technique, is discussed. Particular attention is given to the design of a dielectric multilayer filter which will provide the means of dividing the spectrum into polarized and unpolarized components with the latter being used to calibrate the former.     

A new theta modulation multiplexing scheme for computer-generated holograms

In this paper, a new theta modulation multiplexing scheme for producing multiplexed computer-generated holograms (CGHs) is proposed. Under this scheme, normal Lohmann-type CGHs are individually modulated by gratings with different orientations and then superimposed to form a single hologram. The proposed method results in a higher storage capacity without the increase of hologram space. Theoretical analysis and experimental results are presented.     

象增强高速电影摄影系统MTF及其改善

象增强高速电影摄影在提高探测能力的同时,也引起了成象质量的变化。文章讨论了引起这一变化的各种因素的调制传递函数,给出了在不同的参数下,系统总的调制传递函数数值。并且提出了改善系统MTF的途径。