Phase-step calibration technique based on a two-run-times-two-frame phase-shift method

A novel phase-step calibration technique is presented on the basis of a two-run-times-two-frame phase-shift method. First the symmetry factor M is defined to describe the distribution property of the distorted phase due to phase-shifter miscalibration; then the phase-step calibration technique, in which two sets of two interferograms with a straight fringe pattern are recorded and the phase step is obtained by calculating M of the wrapped phase map, is developed. With this technique, a good mirror is required, but no uniform illumination is needed and no complex mathematical operation is involved. This technique can be carried out in situ and is applicable to any phase shifter, whether linear or nonlinear. (c) 2006 Optical Society of America.

Anomalous behaviour of photorefractive grating erasure owing to existence of both negative and positive carriers

In LiNbO3:Fe, anomalous behaviour of grating erasure is observed with different wavelenghts, i.e. rapid grating erasure in the short wavelength range, which deviates from the results predicted by the electron transport band model. The deviation is related to the coexistance of electrons and holes in photorefraction, and charge-transfer process including electrons and hole has been proposed. The electron and hole contributions to photo-excitation coefficient S of the Fe centre on the wavelength.

Wavefront conversion by local volume holograms between cylindrical and plane waves with reconstruction at a different readout wavelength

Based on the two-dimensional coupled-wave theory, the wavefront conversion between cylindrical and plane waves by local volume holograms recorded at 632.8 nm and reconstructed at 800 nm is investigated. The proposed model can realize the 90 degrees holographic readout at a different readout wavelength. The analytical integral solutions for the amplitudes of the space harmonics of the field inside the transmission geometry are presented. The values of the off-Bragg parameter at the reconstructed process and the diffracted beam's amplitude distribution are analysed. In addition, the dependences of diffraction efficiency on the focal length of the recording cylindrical wave and on the geometrical dimensions of the grating are discussed. Furthermore, the focusing properties of this photorefractive holographic cylindrical lens are analysed.

局域体全息光栅衍射的平面波与柱面波的波前转换研究

利用一维耦合波理论研究了入射方向相互垂直的一束平面波与一束柱面波干涉形成光折变局域体全息光栅的波前转换情况。给出了透射波和衍射波振幅的解析表达式。讨论了该局域体全息光栅的几何尺寸以及全息透镜的焦距对光栅衍射效率的影响。结果表明，随着光栅横向尺寸的增加，光栅的衍射效率也逐渐增加。然而，光栅的衍射效率却随着光栅纵向尺寸的增加而减小。全息透镜的焦距越长，光栅的衍射效率也越大。此外，分析了光栅的布拉格选择特性，该光栅具有非常好的角度选择特性。在平面波与柱面波干涉形成全息透镜的设计中，为了获得最优的衍射效率，应当根

敏化光波长对（Fe，Ni）：LiNbO3晶体全息记录性能的影响

分别采用514nm绿光、488nm蓝光和390nm紫外光作为敏化光，633nm红光作为记录光，详细研究了敏化光波长对氧化（Fe，Ni）：LiNbO3晶体全息记录性能的影响。结果表明：随着敏化光波长的逐渐减小，氧化（Fe，Ni）：LiNbO3晶体的非挥发全息记录性能逐渐优化，390nm紫外光是这三种敏化光中最优的敏化光。考虑敏化光的吸收，为了在双中心全息记录中获得最优的性能，应当选择合适波长的敏化光：一方面短波长敏化光能有效地敏化深中心；另一方面短波长敏化光的吸收太强（如对光折变效应无用的基质吸收），不能沿

双掺杂LiNbO3：Fe：Mn晶体局域光折变体全息光栅形成及衍射特性

将带输运模型与二维耦合波理论相结合，研究了双掺杂LiNbO3：Fe：Mn晶体中由两束有限宽度平面波干涉产生的局域光折变体全息的动力学机制及其衍射特性。采用三步法联立求解了双中心带输运物质波方程和二维耦合波方程。数值计算结果表明，局域光折变体全息光栅的空间电荷场在空间上呈不均匀分布。当光栅区域较小时空间电荷场较强，随着光栅区域的增大，空间电荷场急剧下降，并降低一个数量级。此外，在接近光束入射边界的区域，空间电荷场时空变化规律与一维无限大光折变体全息光栅的结果相似，随着光栅区域的扩大，边界效应对空间电荷场的影

正弦相位调制位移干涉测量技术中调制频率的优化选择

针对正弦相位调制（SPM）干涉测量技术用于位移测量时，调制频率对干涉信号相位解调的影响，提出一种调制频率的优化选择依据。通过对干涉信号的频谱进行分析，发现当被测位移幅度较小时，较小的调制频率即可满足相位解调的要求；而当被测位移较大时，必须相应地增大调制频率，才能获得比较准确的测量结果。模拟计算以及实验结果表明，被测位移信号的幅度每增大四分之一测量光源波长，调制频率需要相应增大4倍于被测信号频率的大小，才能满足正弦相位调制位移干涉测量技术信号处理的需要。

A four-frame phase shift method insensitive to phase shifter nonlinearity

A four-frame phase shift method and an associated algorithm using unequal phase steps are presented. The unique advantage of this method is that it becomes insensitive to phase shifter nonlinearity because of the performance of a special procedure, in which the phase shifts are shared out between the reference beam and the object beam. By this means, any phase shifter can work as long as one phase shift is accurately known. On the basis of the technique, a simple calibration method for the linear phase shifter is suggested. The influences of phase shifter miscalibration, detector nonlinearity and random noise on the algorithm are investigated, and the optimal phase shifts are given.

Distributed measurement of birefringence dispersion in polarization-maintaining fibers

A new method to measure the birefringence dispersion in high-birefringence polarization-maintaining fibers is presented using white-light interferometry. By analyzing broadening of low-coherence interferograms obtained in a scanning Michelson interferometer, the birefringence dispersion and its variation along different fiber sections are acquired with high sensitivity and accuracy. Birefringence dispersions of two PANDA fibers at their operation wavelength are measured to be 0.011 ps/(km nm) and 0.018 ps/(km nm), respectively. Distributed measurement capability of the method is also verified experimentally. (c) 2006 Optical Society of America.

High-efficiency diffraction gratings in fused silica at the wavelength of 632.8 nm

We describe high-efficiency diffraction gratings fabricated in fused silica at the wavelength of 632.8 nm by rigorous coupled-wave analysis (RCWA). High-density holographic gratings, if the groove density falls within the range of 1575-1630 lines/mm and the groove depth within the range of 1.1-1.3 microns, can realize high diffraction efficiencies at the wavelength of 632.8 nm, e.g., the first Bragg diffraction efficiency can theoretically achieve more than 93% both in TE- and TM-polarized incidences, which greatly reduces the polarization-dependent losses. Note that with different groove profiles further optimized, the maximum efficiency of more than 99.69% can be achieved for TM-polarized incidence, or 97.81% for TE-polarized incidence.

基于分支设置的质量导引相位展开算法

二维相位展开方法是近年来较为活跃、引起关注的一个研究课题，它在许多测量应用中有着重要的作用。尽管掩膜阻断算法在多个领域都有成功应用实例，该算法存在着固有的缺陷。为了克服掩膜阻断算法的缺陷，综合分支阻断方法和质量导引方法的优点，提出一种基于分支设置的质量导引相位展开新算法。它先以一个初始质量图来引导分支的设置，然后把分支对应的相位质量设置为最低，从而产生一个新的质量图，最后按新质量图来引导相位展开，并使用几个包裹相位图来验证此方法的有效性。计算机模拟相位图和实际相位图的相位展开结果表明，在存在复杂轮廓不连续

Influence of birefringence dispersion on distributed measurement of polarization coupling in birefringent fibers

A white light interferometer is developed to measure the distributed polarization coupling in high-birefringence polarization-maintaining fibers (PMFs). Usually the birefringence dispersion between two orthogonal eigenmodes of PMFs is neglected in such systems. Theoretical analysis and experimental results show that the birefringence dispersion becomes a nonnegligible factor in a long-fiber test. Significant broadening of interferograms and loss of longitudinal coherence are observed. The spatial resolution and measurement sensitivity of the system decrease correspondingly. Optimum spectrum width selection is presented for better spatial resolution and measurement range. c 2007 Society of Photo-Optical Instrumentation Engineers.

Polarizing beam splitter of a deep-etched fused-silica grating

We described a highly efficient polarizing beam splitter (PBS) of a deep-etched binary-phase fused-silica grating, where TE- and TM-polarized waves are mainly diffracted in the -1st and 0th orders, respectively. Tb achieve a high extinction ratio and diffraction efficiency, the grating depth and period are optimized by using rigorous coupled-wave analysis, which can be well explained based on the modal method with effective indices of the modes for TE/TM polarization. Holographic recording technology and inductively coupled plasma etching are employed to fabricate the fused-silica PBS grating. Experimental results of diffraction efficiencies approaching 80% for a TE-polarized wave in the -1st order and more than 85% for a TM-polarized wave in the 0th order were obtained at a wavelength of 1550 nm. Because of its compact structure and simple fabrication process, which is suitable for mass reproduction, a deep-etched fused-silica grating as a PBS should be a useful device for practical applications. (C) 2007 Optical Society of America

Imaging the earth with ambient noise and earthquakes

In this thesis, I develop the velocity and structure models for the Los Angeles Basin and Southern Peru. The ultimate goal is to better understand the geological processes involved in the basin and subduction zone dynamics. The results are obtained from seismic interferometry using ambient noise and receiver functions using earthquake- generated waves. Some unusual signals specific to the local structures are also studied. The main findings are summarized as follows:

(1) Los Angeles Basin

The shear wave velocities range from 0.5 to 3.0 km/s in the sediments, with lateral gradients at the Newport-Inglewood, Compton-Los Alamitos, and Whittier Faults. The basin is a maximum of 8 km deep along the profile, and the Moho rises to a depth of 17 km under the basin. The basin has a stretch factor of 2.6 in the center decreasing to 1.3 at the edges, and is in approximate isostatic equilibrium. This "high-density" (~1 km spacing) "short-duration" (~1.5 month) experiment may serve as a prototype experiment that will allow basins to be covered by this type of low-cost survey.

(2) Peruvian subduction zone

Two prominent mid-crust structures are revealed in the 70 km thick crust under the Central Andes: a low-velocity zone interpreted as partially molten rocks beneath the Western Cordillera – Altiplano Plateau, and the underthrusting Brazilian Shield beneath the Eastern Cordillera. The low-velocity zone is oblique to the present trench, and possibly indicates the location of the volcanic arcs formed during the steepening of the Oligocene flat slab beneath the Altiplano Plateau.

The Nazca slab changes from normal dipping (~25 degrees) subduction in the southeast to flat subduction in the northwest of the study area. In the flat subduction regime, the slab subducts to ~100 km depth and then remains flat for ~300 km distance before it resumes a normal dipping geometry. The flat part closely follows the topography of the continental Moho above, indicating a strong suction force between the slab and the overriding plate. A high-velocity mantle wedge exists above the western half of the flat slab, which indicates the lack of melting and thus explains the cessation of the volcanism above. The velocity turns to normal values before the slab steepens again, indicating possible resumption of dehydration and ecologitization.

(3) Some unusual signals

Strong higher-mode Rayleigh waves due to the basin structure are observed in the periods less than 5 s. The particle motions provide a good test for distinguishing between the fundamental and higher mode. The precursor and coda waves relative to the interstation Rayleigh waves are observed, and modeled with a strong scatterer located in the active volcanic area in Southern Peru. In contrast with the usual receiver function analysis, multiples are extensively involved in this thesis. In the LA Basin, a good image is only from PpPs multiples, while in Peru, PpPp multiples contribute significantly to the final results.

双中心全息记录的矢量分析与记录方向优化

对描述双掺杂晶体非挥发性全息记录动力学过程的Kukhtarev方程进行了矢量分析, 分析中考虑了体光生伏特效应和外加电场的作用。在小信号近似的基础上给出了双中心全息记录中记录与固定阶段空间电荷场的矢量解析解。在综合考虑空间电荷场的各向异性以及晶体有效电光系数的各向异性后, 给出了双中心全息记录的优化记录方向。结果表明, 对(Fe, Mn):LiNbO3晶体633 nm寻常光记录, 优化记录方向主要由有效电光系数决定, 光栅波矢与光轴夹角为22°, 方位角为30°;对(Fe, Mn):LiNbO3晶体633