【作者】 李艳军；

【导师】 叶声华； 肖海； 邾继贵；

【作者基本信息】 天津大学 ， 测试计量技术及仪器， 2010， 博士

【摘要】 光纤由于其体积小、可弯曲、低损耗、大带宽、不受电磁干扰且对多种物理量具有敏感性等优点,使由光纤构成的器件在传感领域及传光领域都具有非常重要的应用;光学相干层析技术(Optical coherence tomography, OCT)以其非侵入、高分辨率及无创伤等特点,在临床医学及活体组织的实时检测方面具有极大地发展及应用潜力。基于此,本文结合非线性梯度多模光纤的传光特性及OCT系统的原理,研究了一种全光纤结构的共臂分光OCT内窥镜技术,此方法共用信号臂和参考臂,能较好的克服传统OCT技术中由于信号臂和参考臂的分离带来的误差,减少外界环境诸如震动、温度等对系统的影响,并能极大的减小系统体积,为OCT系统的小型化、轻型化应用带来便利。同时利用光纤的光敏特性,对CO2激光照射效应形成长周期光纤光栅的机理进行了研究。论文的主要研究内容包括:1.提出了一种新型的全光纤共臂分光OCT内窥镜技术,通过共臂分光技术虚拟出一个参考面,此参考面可虚拟在被测样品之前、之中或之后的任意位置,从而不会造成参考面及被测样品间的相互遮挡。2.在全光纤共臂分光OCT内窥镜系统中引入转子、定子及离合器机构,使系统轴向扫描和横向扫描分离,同时达到调整OCT探针工作距的目的。3.为实现信号光的扩束及准直,且满足共臂分光OCT内窥镜系统对结构小型化要求,研究了一种基于单模-多模的渐变折射率全光纤准直机构。4.根据光纤的光敏特性,利用Fabry-Perot干涉仪研究了一种测量CO2激光照射效应时所引起光纤折射率改变量的方法。本文通过引入Fabry-Perot干涉仪结构来测量光纤纤芯被照射点处折射率的变化,并以此来研究长周期光纤光栅的形成机理。5.由于频域OCT系统的深度扫描信息由背向散射光谱的傅立叶逆变换获得,从而带来了直流分量及被测样品内部的自干涉及虚像等寄生信息。基于此,本文提出了一种新型的定步长两帧相移算法。此算法极大地降低了OCT系统对虚拟参考面的移动精度要求,且只需要移动一次参考平面,即可消除直流分量及被测样品内部的自干涉。更多还原

【Abstract】 Due to its small volume, capable of being bent, extra low loss, high bandwidth, insensitivity to electro-magnetic and capable of measuring lots of physical quantities, Optical fiber-based devices are wildly used in optical communications and sensing applications; Optical coherence tomography (OCT) is a non-invasive, high-resolution and non-destructive optical technique based on Michelson interferometry which has great potentials in biomedical applications such as clinical medicine and in vivo detection of living tissues. To circumvent the problems mentioned above, an all-fiber common-path beam-splitting OCT endoscopic probe is proposed in this paper. In a common-path interferometer, the reference and sample arm overlap for a significant portion. As a result, it has the advantages of adjustable probe length, reduced sensitivity to vibration and temperature variation, and better stability due to automatically maintained beam overlap. In addition, this miniaturized configuration reduces the complexity and cost of the system. In accordance with the photosensitivity of optical fiber, another research is focused on CO2 laser fabricated long period fiber gratings (LPFG), including the fabrication technique and principles.The research mainly includes:1. A novel common-path OCT probe is demonstrated, which contains a virtual reference plane by using common-path technique. This plane could be located anywhere in front of, in between or behind the sample, free from overlapping of reference plane and investigated sample.2. In the common-path OCT endoscopic system, rotors, stators and clutches are employed to separate A-Scan and B-Scan, and in the meanwhile, to adjust the working distance of OCT probe.3. In order to achieve beam expansion and collimation, and satisfy the need for miniaturized device used in common-path OCT endoscopic system, an all-fiber device using graded-index multimode fiber collimator is investigated.4. A new method to measure the CO2 laser irradiation-induced refractive index modulation in the core of a single-mode optical fiber is demonstrated for the purpose of design and fabrication of LPFGs. The total refractive index change was measured using an optical fiber Fabry–Perot interferometer. The CO2-laser irradiation-induced refractive index change in the fiber core has a negative value and its magnitude is a sensitive function of the laser exposure time following a linear relation. This study provides valuable guidance for LPFG fabrication.5. Owing to the fact that deep scan information from Fourier Domain OCT system is obtained by inverse Fourier transform of back scattered signal spectrum, the acquired images contains parasitic information such as DC signal and self-interference signal along with useful information. Given this drawback, this paper puts forward a new algorithm of fixed-step two frames phase shift. This algorithm significantly lowers the demand for the accuracy of virtual reference plane movement, and only one time movement is needed for eliminating DC signals and self-interference signals inside the sample.更多还原