合成孔径激光成像雷达散斑效应分辨单元成像研究

分析了合成孔径激光成像雷达(SAIL)受散斑效应影响的分辨单元成像过程并推导了含有散斑效应的二维数据收集方程。在此基础上通过数值模拟分析比较了不同接收天线尺寸、不同天线积分起点位置情况下散斑效应对成像所需的光电流交流项、距离向压缩和最终分辨单元成像结果的影响。结果表明散斑效应对分辨单元成像的影响主要体现在降低了分辨单元的图像强度,同时不同天线尺寸和天线积分位置对分辨单元的成像影响差异较大。分析结果可为今后SAIL散斑效应的抑制提供一定的参考。     

平面波导环形格子结构型光交错复用器的设计

在分析比较双折射晶体偏振光干涉型和平面波导环形格子结构型光交错复用滤波器原理的基础上,揭示了两者在光谱透射率的数学上的等效性,给出了两者结构参量之间的等效关系,可以直接利用经简单傅里叶级数对比法获得的晶体的结构参量对平面波导环形格子结构型光交错复用滤波器进行结构设计。利用该方法对一个两级平面波导环形格子结构型光交错复用滤波器进行了优化设计,信道隔离度比文献中结构提高了近5dB,而且结构参量有多种组合。与利用复杂的格子理论计算仅获得一组结构参量相比,该方法更加简单、有效。     

Ti-MCM-41催化环氧化合物与胺的开环反应

以十六烷基三甲基溴化铵(CTAB)为模板剂, 钛酸异丙酯为钛源, 通过水热法合成了Ti-MCM-41分子筛催化剂并对其进行了表征, 结果表明, Ti-MCM-41催化剂具有介孔结构, 其孔径约2.0~4.0 nm. 考察了无溶剂条件下Ti-MCM-41对环氧化合物与胺的开环反应的催化性能. 结果表明, 当反应温度和压力分别为145 ℃和2.5 MPa时, Ti-MCM-41(5)对环氧乙烷(EO)与二甲胺(DMA)的反应具有良好的催化性能, 环氧乙烷的转化率和N,N-二甲基乙醇胺的选择性分别为98.37%和86.68%. 表征结果表明, 催化剂骨架中四配位结构的Ti使其表面具有丰富的路易斯酸性位, 该酸性位对环氧化合物与胺的开环反应具有重要促进作用. 此外, 还对Ti-MCM-41催化环氧乙烷与二甲胺开环反应的机理进行了初步探讨.     

多体制兼容相干探测卫星激光通信技术

卫星相干激光通信系统中,信号调制格式以相移键控(PSK)为主,未兼容开关键控(OOK)的相干接收。针对卫星相干光通信接收机不兼容多种调制格式的问题,实验搭建了兼容OOK以及二进制相移键控(BPSK)的相干通信接收装置。在1 Gbit/s的通信速率下,当调制格式为OOK且信号光功率为-54.6 dBm时,误码率(BER)为10^-3,接收灵敏度距离散粒噪声极限3.3 dB;当调制格式为BPSK且信号光功率为-57.95 dBm时,BER为10^-3,接收灵敏度距离散粒噪声极限4.2 dB。该多体制兼容相干接收机的结构与当前大多数相干接收机的硬件通用,且具有较高的接收灵敏度,证明了卫星相干激光通信多体制兼容技术的可行性,具有重要意义。     

光轴方向任意时光折变晶体中体全息光栅的衍射性质

利用坐标旋转方法和Kogelnik耦合波理论,建立了光轴方向任意时单轴晶体中体光栅布拉格衍射的耦合波方程,分析了Li NbO3晶体的光轴方向对光折变体全息光栅的各向同性和各向异性布拉格衍射性质的影响。模拟计算表明,在给定光栅的结构参量时,通过适当选择光轴方向角可以使得光折变体光栅的各向同性和各向异性布拉格衍射的衍射效率达到最大,给出了相应类型的衍射效率取得最大值时晶体光轴的大致方向。这些理论分析为光折变体全息光学器件的优化设计和进一步广泛应用提供了很好的理论参考依据。     

Material optimization for low scattering noise during nonvolatile holographic recording in doubly doped LiNbO3 crystals

Scattering noises in four kinds of lithium niobate crystals with the same double doping system, which are LiNbO3:Fe:Mn, LiNbOs:Ce:Mn, LiNbOs:Ce:Cu, and LiNbOs:Fe:Cu, are observed and compared experimentally. The results show that nonvolatile holographic recording can effectively suppress scattering noise, which mainly depends on recombination coefficients of both the shallower centers and the deeper centers. The small recombination coefficients of the shallower centers and the large recombination coefficients of the deeper centers benefit the amplification of the signal gratings and the suppression of the noise gratings.In addition, the initial seed scattering also impacts the recorded scattering noise, and the little seed scattering results in low scattering noise. The theoretical simulations are performed for confirmation. Among the four kinds of doubly doped crystals, in LiNbOs:Ce:Cu the performances of nonvolatile recording are the best with low scattering noise and high diffraction efficiency.     

双折射滤波器光谱透射率函数的平坦化优化计算

对于双折射偏振光干涉滤波器，提出了一种产生平坦化光谱透射率函数的傅里叶级数对比的搜索方法，可在较大的通带和阻带范围内寻找到抖动很小时的所有可能的晶体偏转角度的数值解。给出了三块双折射晶体结构的抖动不大于0．1％时的晶体偏转角度的数值解，讨论了晶体偏角和厚度的变化对透射率函数波形的影响。     

Experimental research of circular incoherently synthetic aperture imaging ladar using chirped-laser and heterodyne detection

Synthetic aperture imaging ladar (SAIL) technique belongs fully coherent processing in both the time domain and space domain and has a rather high implement difficulty. To solve this problem, the concept of circular incoherently SAIL is introduced. A speckle version image of a two-dimensional (2D) letter ’E’ target is reconstructed from E-field projection data detected by a circular incoherently SAIL system. The experimental system is constructed by three subsystems using chirped-pulse laser as the light source and heterodyne detection to get the range information of the target. The reconstruction of the image and the noise effect are also discussed in detail.     

The photorefractive sensitivity and the effective electron transport length in two-centre holographic recording

In this paper the photorefractive sensitivity defined for single-centre holographic recording is modified to adapt two-centre holographic recording. Based on the time analytic solution of Kukhtarev equations for doubly doped crystals, the analytical expression of photorefractive sensitivity is given. For comparison with single-centre holographic recording and summing the electron competition effects between the deeper and shallower traps, an effective electron transport length is proposed, which varies with the intensity ratios of recording light to sensitive light. According to analyses in this paper, the lower photorefractive sensitivity in two-centre holographic recording is mainly due to the lower concentration of unionized dopants in the shallower centre and the lower effective electron transport length.