【作者】 廖然；

【导师】 何赛灵；

【作者基本信息】 浙江大学 ， 光学工程， 2007， 博士

【摘要】 本论文主要介绍了利用光散射数据来进行无损检测和成像的研究。光散射现象是自然界中的普遍现象，基于光散射的无损检测和成像技术也是现代科学一直在关注的课题。在本文中，我们主要集中在波导中的缺陷引起的光散射现象和混沌介质(比如生物组织和悬浊液等)中的光散射现象。本论文分两个部分，其中一部分研究当入射波被波导中的缺陷散射后，如何从波导两端的接收到散射数据中，用解析方法，重构出缺陷在波导中的位置以及缺陷的光学特性；其中一部分是研究了一种对高散射介质非常有效的成像技术——OCT。我们回顾了OCT的历史和基本原理；基于Mie散射理论和Monte Carlo方法，开发了数值模拟模型，通过模拟发现空间滤波和偏振门可以提高OCT的层析成像能力和对比度；我们开发了OCT实验系统，并且做了成像实验；还开发了针对样品色散的补偿算法。本文共分八章，各章的主要内容如下：第一章绪论。回顾了现代科学对光散射现象的研究历史；分析了光被介质散射后的散射光的分类；提出了人们分析光散射现象的四条途径：解析理论、输运理论、实验和数值模拟；以及人们利用光散射现象在检测和成像领域中的应用，重点介绍了DOT(diffused optical tomography)和OCT(Optical coherence tomography)。第二章到第四章讲到如何利用波导两端的散射光来检测波导中的缺陷，包括它的位置和光学性质。第二章从电磁场理论出发推导了出描述二维波导的方程，并且给出了解这个方程的数值解——MOM(Method of Moments)。第三章和第四章分别从第二章所得到的方程出发，结合界磁场理论，开发了重构出波导中一个点缺陷或者一个细条缺陷的方法。让一束导模光入射到波导中，入射光会被波导中的缺陷(点缺陷或者细条缺陷)散射，在波导两端测量散射场，然后利用我们的重构算法，就可以得到缺陷的位置和光学性质。第五章讲OCT的基本原理。首先介绍了低相干原理，推到了低相干光干涉信号的公式；然后结合OCT的基本结构，给出了OCT的一些性能参数。第六章讲到OCT系统的模拟。我们基于Mie散射理论和Monte Carlo方法，来建立OCT的数值模型；经过数值模拟，我们验证了OCT的层析能力，并且经过考察发现空间滤波和偏振门能够提高OCT分辨力和信号对比度。我们建立了有限光斑大小光源的OCT模型，并且我们发现了被其他研究者证实了的浴幕效应。第七章讲OCT实验系统。首先分别介绍了我们自己开发的实验系统的硬件和软件；基于我们自己设计的OCT系统，针对悬浊液、植物样品、牙齿和宝石等进行了成像实验，验证了我们系统的成像能力。另外，我们分析了样品引入的色散对OCT信号的影响，并且设计了数值算法来补偿其负面影响。第八章给出了整篇论文的总结，并且就波导中缺陷检测问题和以OCT为工具的混沌介质检测和成像问题，给出了一些未来努力的方向，和研究的思路。更多还原

【Abstract】 Optical scattering is a basic phenomenon found in nature, and researchers around the world have paid much attention to the techniques of non-invasive detection and imaging based on optical scattering. The purpose of this thesis is focused on the research of non-invasive optical detection and imaging by use of scattering data.The thesis consists of two parts. The first part describes the measurement of the scattered field or intensity distribution at the two end face of the waveguide, and the reconstruction formulas to find the location and optical properties of the defects in the waveguide. The second part describes the study of optical coherence tomography (OCT)—a very powerful imaging technique for high scattering media. The history and principles are reviewed, and several numerical models, based on Mie theory and Monte Carlo techniques, are given. By numerical simulations, we have found that proper space filtering and polarization gating can increase the contrast and the resolving power of an OCT system. We have developed OCT systems and do some imaging experiments; and we also have developed an algorithm to compensate the dispersion of the samples.The thesis is divided into eight chapters, the summaries of which are as followes:Chapter 1 is about introduction. In this chapter we review the history of the research of optical scattering since modern science starts. The scattered lights are characterized according to the time domain and the space domain, and different research methods, such as analytical theory, transport theory, experimental and numerical simulation, are introduced. Subsequently we give the introduction of techniques based on optical scattering, diffused optical tomography (DOT) and OCT.Chapter 2 - 4 are about the analytical reconstruction method which is useful to find the location and optical properties of the defects in waveguides. In Chapter 2, we first deduce the two dimension (2D) partial equation for the optical scattering in a waveguide, based on Maxwell’s equations; and then introduce a numerical method -methods of the moments (MOM) to solve the 2D partial equation. In Chapter 3 and 4, we show the algorithms to reconstruct the location and optical properties when there is only one point defect or one thin-strip defect in the waveguide, based on the knowledge in Chapter 1. When a guided mode is excited inside a planar waveguide,the presence of the defect (a point defect or a thin-strip defect) will cause a distortion of the field distribution in the waveguide. Such a field distortion can be measured (with, e.g., a CCD camera) at the two end faces of the planar waveguide and used to predict the location and width of the thin strip defect.Chapter 5 is about principles of OCT systems. We first introduce the principles of low coherence interferometry, and deduce some formulas for the interferometric signals. Then we give the classical structure and some performance coefficients of OCT systems.Chapter 6 is about simulation of OCT. We have developed a numerical model of OCT, based on Mie theory and Monte Carlo technique; by simulation, we have verified resolving power of OCT system; and found that space filtering and polarization gate could increase the contrast and resolving power of OCT system. Finally, we used our model to study the lateral resolution when the sample is illuminated by finite-spot source. We have found the shower curtain effect, which was observed by other researcher in experiments.Chapter 7 is about OCT experiment system. At first, we introduce the OCT system developed by ourselves, including hardware and software. We have done some imaging experiments by use of our OCT system, and the samples include suspension, segments of onion, tooth of human being, and jade, and our system performed well. At the end, we have discussed the influence to OCT signal of dispersion caused by samples, and then we develop a numerical algorithm to compensate it.Chapter 8 is the conclusion and expectation. We draw a conclusion and give some key problems and developing trends for future work of non-invasive optical detection and imaging by use of scattering data.更多还原