混合干涉型分布式光纤传感器PGC信号解调设计与实验分析

对一种基于马赫-曾德尔和萨格纳克混合干涉仪原理的分布式光纤泄漏检测系统调制解调技术进行研究,对PGC解调技术进行理论分析。针对所选泄漏分布式光纤传感特点设计了PGC解调硬件电路,并对PGC解调电路进行了测试。实验中待测信号为0~50 kHz,载波频率为300 kHz,截止频率为50 kHz, 移相后与待测信号的相关系数达到0.95,谐波失真小于3%,泄漏源位置为7.865 km,泄漏检测定位系统绝对定位误差为235 m,相对定位误差为2.35%。本解调定位系统具有稳定性和抗干扰性。     

Fiber-Optic Current Sensor Using Passive Demodulation Interferometric Scheme

An interferometer using a Faraday rotator with 22.5 rotation bias is proposed for the use of a fiber-optic current sensor (FOCS) to demodulate phase signals passively. High sensitivities and extra low distortions are obtained by this passive demodulation interferometric scheme (PDIS). The Verdet constant of optical fibers at 1300 nm is evaluated to be 4.5 murad (A rms.turns), which is in good agreement with the literature. With signal distortions always below 0.8 %, the proposed scheme should be significantly effective for the demodulation needs of an FOCS. The PDIS also could enable a FOCS to directly connect with fiber-optic communication networks for the implementation of long-distance remote and multiplexing sensor systems. Moreover, electric shock concerns on current intensity measurements of high-voltage power delivery systems are greatly reduced.     

大气光学湍流光纤测量技术中的解调算法研究

介绍了直接调制光源型光纤Mach-Zehnder干涉仪测量大气光学湍流的原理,并对其中的载频调制和解调的过程进行了深入的研究.通过计算机对光学湍流随机相位起伏、载频调制与解调过程的模拟证明了直接调制光源型光纤Mach-Zehnder干涉仪测量大气光学湍流的可行性,提出大气光学湍流光纤测量技术中的一种新的信号处理方法.     

Field-based angle-resolved light-scattering study of single live cells

We perform field-based angle-resolved light-scattering measurements from single live cells. We use a laser interferometer to acquire phase and amplitude images of cells at the image plane. The angular scattering spectrum is calculated from the Fourier transform of the field transmitted through the cells. A concurrent 3D refractive index distribution of the same cells is measured using tomographic phase microscopy. By measuring transient increases in light scattering by single cells during exposure to acetic acid, we correlate the scattering properties of single cells with their refractive index distributions and show that results are in good agreement with a model based on the Born approximation.     

Application of passive quadrature phase demodulation for the detection of laser ultrasound

In this paper we describe a laser ultrasound detection scheme based on a new passive phase demodulation technique. Typical laser interferometers suffer from the loss of sensitivity because of phase drifts resulting from the mechanical movements of optical components and normally require closed loop stabilisation control. Through the use of a custom-designed grating mask, the present design completely eliminates the need for any feedback control by simultaneously sampling the interferometer output in the four quadrants of the optical phase circle. The signals are then processed to reproduce the actual waveform of the ultrasound pulse. The operation of the proposed technique is demonstrated through the detection of laser-generated ultrasound waves propagating inside an aluminium block.     

Introduction of the Impulse Response Function in Common-Path Interferometers with Fourier Plane Filters

In the present paper it will be shown how the introduction of a Fourier plane filter can create various types of common-path interferometers for measuring changes in surface tilt or curvature of an object surface. This is obtained by placing a holographic optical element in the Fourier plane of a 4-f optical system. The interferometers are analysed by using the paraxial approximation of the Huygens-Fresnel integral formalism, and the interferometer functions are given by a novel formalism using impulse response functions. Based on this technique, an interferometer for measuring dedicated changes in surface deflection is presented. This interferometer is insensitive to rigid surface rotations and displacements. The interferometer can be embedded in systems based on single point measurement of a time dependent deflection, i.e. vibrometers, as well as in full-field measurements such as electronic speckle interferometers.This paper was originally presented at the 2001 International Conference (2nd Joint OSJ-SPIE Conference) on Optical Engineering for Sensing and Nanotechnology, ICOSN 2001 which was held June 6-8, 2001 at the Pacifico-Yokohama Conference Center, Yokohama, Japan.     

基于光子晶体马赫-曾德尔干涉仪的太赫兹开关及强度调制器

通过对二维正方晶格光子晶体线缺陷模色散曲线慢光特性的研究, 利用外电场对液晶分子取向的调控作用, 在填充液晶的正方晶格波导的马赫-曾德尔干涉仪结构中实现了开关和强度调制等功能. 利用平面波展开法计算了光子晶体波导的线缺陷模, 分析了液晶折射率的变化对缺陷模的影响. 计算表明, 液晶折射率仅改变了0.1, 线缺陷模有效折射率改变达0.168, 该特性可以更为有效地实现对相位的控制, 进而实现高消光比开关和强度调制功能, 这种高效的相位调节器件在集成光系统中将有很好的应用前景.     

基于强度传输方程的相位检索

为了从直接测量的强度图像中计算出相位信息,研究了基于强度传输方程的相位检索技术.设计了一个实用的相位检索系统,包含经典傅里叶相位检索和基于整体变分的相位检索算法.通过测量聚焦平面和前后散焦平面光波场的空间强度,求解二阶微分方程得到相位.与迭代相位检索技术相比克服了其迭代不确定性、收敛速度慢等缺点.实验表明,利用强度传输...     

Lissajous figures in the application of micro-vibration measurement

Based on Michelson interferometer and phase generated carrier (PGC) homodyne demodulation technique, an optical interferometer system is built, and a novel method using the central angles of Lissajous figures to measure micro-vibration displacement is proposed. The Lissajous figures are obtained by synthesizing two interferometric signals that their vibration directions are orthogonal and their intensities are equal. Through theoretical analysis, software simulation and experimental test, it is concluded that the central angles of Lissajous figures have a linear relationship with the phase modulation coefficients and the micro-vibration displacements when the phase modulation coefficients are small. So the micro-vibration displacements can be directly obtained by measuring the central angles of Lissajous figures. The method is simple and convenient. The experimental results indicate that the micro-vibration displacements measuring range can reach 5-775 nm, with a resolution of about 5 nm.     

Slow light using wave mixing in liquid crystal light valve

By performing optical two-wave mixing in a liquid crystal light valve, we are able to slow down optical pulses to group velocities as slow as a few tenths of mm/s, corresponding to a very large group index. We present experiment and model of the slow light process occurring in liquid crystal light valves. The large group index corresponds to having a large sensitivity for phase variations, a property that can be used to increase the sensitivity of Fourier transform interferometer. We show that when a liquid crystal light valve is inserted in a Mach–Zehnder interferometer, the effect of frequency perturbations at the input of the system is amplified by a factor related to the group delay.     

Interferometric focal length measurement of power-distributed lenses

An interferometric method for measuring the focal length of power-distributed lenses is described. The test lens is illuminated by a regular pitch interferometric pattern produced by a reflective diffraction grating interferometer. In order to measure the focal length, a CCD camera digitizes the image of the pattern magnified by the lens, and fast Fourier transformed to reconstruct the phase modulo 2π along each row. The change in spatial frequency is determined by unwrapping the phase along each row of the digitized imaged pattern. The technique is used for measuring the focal length distribution inside the progression corridor of both positive and negative progressive lenses.     

Downstream Fabry-Perot interferometer for acoustic wave monitoring in photoacoustic tomography

An optical detection setup consisting of a focused laser beam fed into a downstream Fabry-Perot interferometer (FPI) for demodulation of acoustically generated optical phase variations is investigated for its applicability in photoacoustic tomography. The device measures the time derivative of acoustic signals integrated along the beam. Compared to a setup where the detection beam is part of a Mach-Zehnder interferometer, the signal-to-noise ratio of the FPI is lower, but the image quality of the two devices is similar. Using the FPI in a photoacoustic tomograph allows scanning the probe beam around the imaging object without moving the latter.     

Phase profile analysis of transparent objects through the use of a two windows interferometer based on a one beam splitter configuration

In this research we implemented a two windows interferometer based on polarization phase shifting and grating interferometry techniques in order to retrieve the phase data profile of the object in a single capture. The optical configuration has two optical beams with circular polarization in opposite directions, and it is coupled with a 4-f system. An amplitude grid is used as a filter which is placed at the Fourier plane to obtain replicas of each beam which can properly interfere, depending on the separation between beams. The interferometer presents the capability of changing the beam separation in order to make different orders interfere properly. The interference patterns produced can be separately modulated through the operation of linear polarizer's placed on each interference replica. In order to present the capabilities of the system we will select four interferograms result of contiguous orders interference.     

Single-optical-element soft-x-ray interferometry with a laser-plasma x-ray source

We report on a compact interferometer for the water-window soft-x-ray range that is suitable for operation with laser-plasma sources. The interferometer consists of a single diffractive optical element that focuses impinging x rays to two focal spots. The light from these two secondary sources forms the interference pattern. The interferometer was operated with a liquid-nitrogen jet laser-plasma source at lambda=2.88 nm. Scalar wave-field propagation was used to simulate the interference pattern, showing good correspondence between theoretical and experimental results. The diffractive optical element can simultaneously be used as an imaging optic, and we demonstrate soft-x-ray microscopy with interferometric contrast enhancement of a phase object.     

干涉型光纤传感器相位生成载波解调方法改进与研究

提出了基于干涉型光纤传感器的相位生成载波解调方法（PGC）的改进方法,通过算法上的改进和增加抗混叠滤波器,有效地改善了解调结果,并大大降低了系统的采样频率,结论对设计干涉型光纤传感器解调系统有重要的参考意义     

The new method of topological charge determination of optical vortices in the interference field of the optical vortex interferometer

In this paper, the new method of determination of the topological charge of vortex points in the interference field obtained by three plane waves interference is presented. Such optical fields are used in the optical vortex interferometer (OVI) and the determination of vortex points’ topological charge allows of unique determination of the relative phase between interfering waves (phase unwrapping problem). The new method uses additional plane wave, which produce a characteristic fork-like fringe structure in the neighbourhood of vortex points. By analysing the orientation of these fork-like patterns one can read the sign of the topological charge of the given vortex point. The method is simple and can be used for OVI calibration performed before the measurements.     

Carrier fringes in the two-aperture common-path interferometer

We present a method to introduce a linear phase into an interference pattern. This phase is introduced when a grating is placed outside of the Fourier plane of a two-aperture common-path interferometer, which is built using a 4f optical imaging system. Based on an analysis of near-field diffraction, the introduction of the carrier fringes is mathematically justified. It is important to note that no tilt between the two beams is requested to produce this effect, and it turns out to be simpler, easier, and more versatile than other existing methods. The main attributes and advantages of the setup will be discussed and illustrated in detail with experimental fringe patterns.     

基于强度传输方程的相位检索

为了从直接测量的强度图像中计算出相位信息,研究了基于强度传输方程的相位检索技术.设计了一个实用的相位检索系统,包含经典傅里叶相位检索和基于整体变分的相位检索算法.通过测量聚焦平面和前后散焦平面光波场的空间强度,求解二阶微分方程得到相位.与迭代相位检索技术相比克服了其迭代不确定性、收敛速度慢等缺点.实验表明,利用强度传输方程检索相位的方法可以有效快速地从强度图像中计算出相位|整体变分算法相比傅里叶算法,在恢复相位的同时可以保持良好的边缘.     

基于莫尔干涉的激光中心波长精确检测的研究

为了提高激光中心波长检测的精确度,提出了基于正交干涉原理的静态干涉系统,由两个相互垂直的棱镜组成产生二维平面上的光程差分布,以面阵CCD取代线阵CCD,对平面上的正交干涉条纹数据进行采集.在计算分析莫尔干涉仪的光程差分布的基础上,计算干涉图像中干涉条纹的拼接及傅氏变换等,最终得到光谱分辨率.由MATLAB仿真软件分析结果可知,静态莫尔干涉系统可以产生的光程差最大为234μm,比等尺寸的傅里叶干涉体高约一个数量级.实验标定用的光谱仪选用LAB SPAKR 750A型光谱仪,针对中心波长为635 nm的半导体激光器进行测量,结果显示中心波长位置基本一致,但在中心波长附近的光谱细节上莫尔干涉优于传统干涉具.     

Phase shifting grating-slit test utilizing a liquid crystal display

A quantified focal plane testing method, termed phase-shifting grating-slit test, is demonstrated by utilizing a micro liquid crystal display. In contrast to the setup in the Ronchi Test, an incoherent illuminating grating is used and an optical slit is located at the image plane of the tested lens to modulate the aberrated wavefront. With the micro liquid crystal display generating and phase shifting the incoherent illuminating grating with variable frequency, a higher measurement dynamic range can be achieved on demand.