Large-scale absolute distance measurement with dual free-running all-polarization-maintaining femtosecond fiber lasers

We demonstrate a robust femtosecond LIDAR setup by using two free-running environmentally stable allpolarization-maintaining nonlinear amplified loop mirror mode-locked fiber lasers. Based on the asynchronous optical sampling method, a ranging accuracy of ±2 μm within 65 m has been achieved, as tested in an 80-m-long underground optical tunnel. Through the Kalman filter in real-time data processing, the measurement accuracy can be maintained at a 200 Hz update rate. This setup provides a practical tool for various large-scale industrial and astronomical ranging applications.     

Holographic Grating Formation in Cationic Photopolymers with Dark Reaction

We propose a new formula to describe the dynamics of holographic grating formation under low intensity pulse exposures in cationic photopolymers, in which the dark reaction contributes dominantly to the grating strength. The formula is based on the living polymerization mechanism and the diffusion-free approximation. The analytical solution indicates that the grating formation time depends on the termination rate constant, while the final grating strength depends linearly on the total exposure energy. These theoretical predictions are verified experimentally using the Aprilis HMC-400μm photopolymer. The results can provide guidelines for the control and optimization of the holographic recording conditions in practical applications.     

枕形柱正方晶格二维宽完全带隙光子晶体的全息设计

提出了一种利用多光束全息干涉产生类似结构的方法,系统分析了制备条件对所得结构能带性质的影响,证明这种具有枕形柱的正方晶体可以产生比最佳设计的正方形柱晶体更宽的完全带隙,同时给出了该全息结构的光学制备方法,包括各光束的波矢及偏振态。     

基于级联分数傅里叶变换系统的数字水印技术

提出一种基于分数傅里叶变换和随机相位编码的光学加密数字水印技术,可成为一种信息隐藏及保护的有效方案.该数字水印技术对于噪音叠加和常见的图像处理操作具有较强的稳健性.该技术根据光学级联分数傅里叶变换系统,利用两个随机相位分布函数对水印信息编码并经过迭代分数傅里叶变换嵌入到变换域的载体图像中.在水印检测和提取过程中,两个相位分布函数作为密钥.随机相位编码技术的引入,进一步提高了数字水印系统的密钥空间.增强了系统的安全性.该数字水印技术基于光学分数傅里叶变换原理,可以利用光学变换系统方便地实现.     

基于相位补偿的调频连续波大长度测距中的色散校正

基于调频连续波测距的原理搭建并改进了双光路调频连续波测距系统,在测量光路增加光纤延迟线使测量距离拓展到了65 m.还研究了等光频重采样中色散的影响,推导出了带有色散和光纤延迟线的重采样模型,提出了在调频连续波大长度测距中通过频率幅度来调节相位补偿系数的色散校正方法.实验表明,在45~65 m的范围内增加了光纤延迟线并且有效的校正了色散,校正色散后在65. 165 m处测距值与干涉仪测量值最大误差小于500μm,标准差为246μm,频谱分辨力高达123μm,十分接近理论分辨力.文章的研究为调频连续波大尺寸测量提供了可行性的参考.     

外差干涉相位测量中信号串扰误差与补偿方法研究

为了解决外差干涉相位测量中多通道采样信号间的串扰误差对相位测量精度的影响，提出了一种基于采样信号频谱分析的预补偿方法来实现信号串扰误差的补偿和消除。首先建立基于锁相放大的正交鉴相法的信号串扰误差理论模型，阐明了串扰系数、输入信号幅值比和串扰信号相位偏移对相位测量误差的影响；设计仿真实验验证了该误差模型和补偿方法的有效性；然后基于紧凑型FPGA开发平台设计了相位测量实验，结果表明该补偿方法能够有效消除信号串扰误差的影响，补偿后相位测量的最大误差从0.34°下降到0.01°；最后搭建了外差干涉仪并与高精度的压电位移平台进行比对，实验结果表明补偿后的信号处理系统能够满足外差干涉测量的应用需求。