碳涂覆光纤表面碳膜形成机理研究

通过分析碳涂覆光纤的测试结果，研究碳涂覆光纤碳膜的形成机理，并应用该机理解释涂覆光纤的高可靠性问题和影响光纤初始强度大小的因素。     

气密性碳涂覆光纤筛选强度与电阻关系研究

通过实验分析确立了把光纤电阻作为衡量气密性碳涂覆光纤通过２％应变筛选的过渡标准。要拉制２％应变筛选的碳涂覆光纤，其电阻值应小于３０ｋΩ／ｃｍ。     

一种碳涂覆光纤碳膜厚度在线控制技术

为了控制长长度碳涂覆光纤和对光纤碳膜厚度进行了在线监控,开发了一种碳涂覆光纤碳膜厚度在线监控技术。试验结果表明,这种技术是行之有效的。     

一种特殊截止单模光纤的传输性能研究

为了提高特殊截止单模光纤的弯曲可靠性,采用气相沉积工艺制作了包层直径80μm碳涂覆的特殊截止单模光纤,测试了光纤的截止波长、模场、衰减谱、宏弯、色散等传输性能和应力腐蚀敏感性参数。测试结果表明光纤截止波长小于915nm,能够实现915nm以上波长单模工作,在常用的几个波段具有较低的传输损耗,光纤的零色散波长红移到1 670nm。采用碳涂覆工艺提高光纤的应力腐蚀敏感性参数达到35,结合小包层直径预期可以提高光纤的使用寿命。     

飞秒激光制备光纤布拉格光栅高温传感器研究

光纤布拉格光栅具有体积小、耐腐蚀、抗电磁干扰、传感灵敏度高、可实现准分布式测量等优点,是一种重要的光纤传感器件。传统紫外激光制备光纤布拉格光栅时需要对光纤进行载氢预处理,这种方法制备的光纤光栅热稳定较差,无法用于极端高温环境。近年来,随着飞秒激光在玻璃材料微加工领域研究的深入,研究人员开始将飞秒激光应用于光纤光栅的研制,飞秒激光制备光纤光栅具有更好的加工灵活性,无需对光纤进行载氢预处理,也无需剥除光纤涂覆层,而且飞秒光纤光栅具有极佳的高温稳定性。介绍了光纤光栅的飞秒激光加工机理,以及三种典型的光纤光栅飞秒激光制备方法,综述了飞秒光纤布拉格光栅在高温传感领域的研究进展。     

一种简易的光纤光栅涂覆装置

阐述了对裸光纤光栅进行涂覆的原理和必要性。设计了一种简易可行的光纤光栅涂覆装置。该装置简单灵活,成本较低,尤其适合于长度较长的光纤光栅的一次性涂覆,涂层厚度灵活可调。以啁啾光纤光栅为例进行了涂覆实验,涂层光滑均匀,涂覆后的光栅强度得到了增强,抵抗机械应力的能力得到了提高,使用起来更方便。对光栅在涂覆前后分别作了特性参数测试。结果表明,光栅特性基本上不发生变化,性能未劣化,光纤光栅的涂覆简单易行。     

聚酰亚胺涂覆的光纤宏弯温度传感器

为了提高光纤宏弯温度传感器的性能,提出了一种基于聚酰亚胺(PI)涂覆的新颖光纤宏弯温度传感器。利用基于纤芯-包层-无限涂覆层结构的光纤弯曲损耗-温度测量方法确定了传感器的光纤弯曲半径,将PI薄膜涂覆在1060-XP光纤包层外获得了新型的光纤宏弯温度传感器。该传感器的温度传感实验结果表明,PI涂覆不仅能提升光纤的机械性能和耐热性,还可实现温度灵敏度和温度测量分辨能力的显著提高。该新颖的光纤宏弯温度传感器可实现-20～100℃的宽温测量范围,温度灵敏度为0.072 dB/℃,分辨能力为0.14℃。与其他光纤宏弯温度传感器相比,所设计的传感器的温度传感性能显著提高。     

光纤型热光可调光衰减器的设计及其衰减分析

提出了一种基于热光调节的可调光衰减器结构。该衰减器通过腐蚀光纤包层到一定厚度和长度后,在表面涂覆较大热光系数的聚合物材料得到。从模场变化角度分析了传输光束的衰减与涂覆材料折射率的关系,并从实验上测试了使用不同涂覆材料时的衰减。理论分析与实验结果均表明在涂覆材料折射率略大于原光纤包层材料折射率时,涂覆材料折射率微小的变化将引起传播光束衰减的大幅度变化,并且光纤被腐蚀的长度越长或包层材料剩余厚度越小,衰减越大。因此,由热光系数大、折射率略大于光纤包层的聚合物材料所组成的可调光纤衰减器,具有衰减调节范围大且功耗小、插入损耗小、成本低、低偏振特性、易于与其它光纤器件耦合或集成等特点。     

保偏光纤在线定轴技术研究

研究了熊猫型保偏光纤在带涂覆层时的POL（polarization observation by lens-effect-tracing method）特性,说明用于去涂覆裸光纤的POL定轴技术同样适用于带涂覆情况,而且可达到相同的定轴精度.建立了一个初步的实验系统对熊猫型保偏光纤的在线定轴技术进行了系统的研究,采用曲线拟合和相关技术大大减小了各种定轴误差.在此系统上已可达到优于2°的定轴精度.     

含耐高温涂覆层长周期光纤光栅的温度特性研究

利用逐点写入法在耐高温光纤中用红外飞秒激光直接写入了长周期光纤光栅,研究了光栅的高温温度特性,并做了理论分析.通过对含耐高温涂覆层的长周期光纤光栅进行20 ℃~300 ℃的温度传感实验,结果表明：在高温段光栅的谐振波长漂移量与温度之间仍能保持大的灵敏度（0.060 5 nm/℃）和好的线性度,且光纤耐高温涂覆层不受破坏,光纤耐高温涂覆在高温下不会出现碳化现象,光栅传感性能良好.实验证明该方法制作的光栅适合于长期在高温环境下使用,应用价值巨大.     

Investigation of cladding and coating stripping methods for specialty optical fibers

Fiber optic sensing technology is used extensively in several engineering fields, including smart structures, health and usage monitoring, non-destructive testing, minimum invasive sensing, safety monitoring, and other advanced measurement fields. A general optical fiber consists of a core, cladding, and coating layers. Many sensing principles require that the cladding or coating layer should be removed or modified. In addition, since different sensing systems are needed for different types of optical fibers, it is very important to find and sort out the suitable cladding or coating removal method for a particular fiber. This study focuses on finding the cladding and coating stripping methods for four recent specialty optical fibers, namely: hard polymer-clad fiber, graded-index plastic optical fiber, copper/carbon-coated optical fiber, and aluminum-coated optical fiber. Several methods, including novel laser stripping and conventional chemical and mechanical stripping, were tried to determine the most suitable and efficient technique. Microscopic investigation of the fiber surfaces was used to visually evaluate the mechanical reliability. Optical time domain reflectometric signals of the successful removal cases were investigated to further examine the optical reliability. Based on our results, we describe and summarize the successful and unsuccessful methods.     

Optical backpropagation for fiber-optic communications using optical phase conjugation at the receiver

A fiber-optic system design with optical backpropagation that uses an optical phase conjugator, high-dispersion fibers, and highly nonlinear fibers is investigated. The proposed technique outperforms the midpoint optical phase conjugation and digital backpropagation with the same step size.     

Microstructured fibers with highly nonlinear materials

We investigated the effect of modification of silica with high concentrations of germanium up to 36 mol% as well as with highly polarizable dopants (e.g., barium and lanthanum) on optical behavior of microstructured fibers. The goal was to investigate the influence of doping on several properties like fiber attenuation, supercontinuum generation and birefringence in microstructured optical fibers (MOF).     

Polymer Optical Fiber Photosensitivities and Highly Tunable Fiber Gratings

In this paper, recent progress in the investigation of photosensitivities of polymer optical fibers and the development of polymer optical fiber grating is reported. Photosensitivities in various polymer fibers, including doped and undoped, multimode and single-mode polymer fibers, have been experimentally characterized and evaluated for fiber grating application. In particular, the wavelength dependence of material absorption and photosensitivity has been found essential to the fabrication of polymer optical fiber grating. Based on the results of photosensitivity research, polymer optical fiber gratings have been successfully fabricated. More importantly, polymer optical fiber grating has been demonstrated highly tunable, with a tuning range more than 70 nm. The unique feature of high tunability in polymer optical fiber grating has great potential in various applications including optical fiber WDM systems and fiber sensor systems. Several important issues that remain to be investigated will also be discussed.     

Polymer Optical Fiber Photosensitivities and Highly Tunable Fiber Gratings

In this paper, recent progress in the investigation of photosensitivities of polymer optical fibers and the development of polymer optical fiber grating is reported. Photosensitivities in various polymer fibers, including doped and undoped, multimode and single-mode polymer fibers, have been experimentally characterized and evaluated for fiber grating application. In particular, the wavelength dependence of material absorption and photosensitivity has been found essential to the fabrication of polymer optical fiber grating. Based on the results of photosensitivity research, polymer optical fiber gratings have been successfully fabricated. More importantly, polymer optical fiber grating has been demonstrated highly tunable, with a tuning range more than 70 nm. The unique feature of high tunability in polymer optical fiber grating has great potential in various applications including optical fiber WDM systems and fiber sensor systems. Several important issues that remain to be investigated will also be discussed.     

Microstructured Ultrathin HDPE Films Prepared by Selective Oriented Recrystallization

The recrystallization behavior of surface-modified melt-drawn HDPE thin films having a vacuum-evaporated carbon layer was studied by means of transmission electron microscopy and electron diffraction. The results show that, by surface modification with the carbon layer, the orientation of the melt-drawn highly oriented HDPE film can be preserved after complete melting and subsequent recrystallization for any condition. Based on the orientation maintenance phenomenon of the carbon-coated preoriented HDPE films, micrometer-structured, thin HDPE films with well-defined oriented and nonoriented structures were prepared by selectively coating the melt-drawn-oriented HDPE thin film with the help of a micrometer-structured mask and subsequent melt recrystallization. A potential application of the thus prepared micrometer-structured HDPE thin films stems from the fact that they exhibit conspicuous different birefringence between the areas with and without carbon coating under polarized optical microscopy. This may provide us with a new route toward polarization-dependent displays.     

Fiberoptic infrared radiometer for real time in situ thermometry inside an MRI system

A warm body emits radiation whose intensity I is dependent on the surface temperature T. For T near room temperature this radiation is mostly in the mid-IR. Radiometric measurement of I is often used for non contact thermometry. Temperature measurements in situ and in remote locations can be carried out using optical fibers, but one needs fibers that are highly transparent in the mid-IR. Our group has developed fibers made of silver halides. These are flexible, nontoxic, not hygroscopic and highly transparent in the mid IR. These fibers served for the development of a novel fiberoptic radiometer. Using this radiometer we have measured the temperatures of samples while being imaged in an MRI system. The presence of the fibers inside the MRI system did not interfere with the operation of the MRI nor did not the MRI system affect the radiometer. The temperature measurements were made with accuracy of 0.3 degrees C, response time of 1 s and spatial resolution of 1 mm. Fiberoptic radiometers would be highly suitable for temperature measurement of human tissues, for example during surgical procedures done inside an MRI system.     

Integrating liquid crystal based optical devices in photonic crystal fibers

Liquid crystal photonic bandgap fibers form a versatile and robust platform for designing optical fiber devices, which are highly tunable and exhibit novel optical properties for manipulation of guided light. We present fiber devices for spectral filtering and polarization control/analysis.     

Light propagation in highly birefringent photonic liquid crystal fibers

Photonic liquid crystal fibers have already been demonstrated as a promising perspective for creation of new classes of dynamically tunable optical fiber devices. By combining different geometries of photonic crystal fibers with a variety of different liquid crystals it is possible to obtain a new generation of fibers with dynamically tunable properties, e.g., transmission spectra, attenuation or dispersion. In this paper, tunable birefringence in a commercially available highly birefringent Blazephotonics PM-1550-01 photonic crystal fiber selectively filled with a low birefringence liquid crystal has been experimentally demonstrated. Theses experimental results have been compared with simulations based on the multipole method.     

Nonlinear refractive indices of nonlinear liquids: wavelength dependence and influence of retarded response

We use liquid-filled capillary fibers with different core diameters to precisely characterize the nonlinear refractive index of the highly nonlinear liquids carbon disulfide, nitrobenzene, and toluene. We present measurements with two different femtosecond pump sources at wavelengths of 1032 and 1560 nm. The large nonlinearity of the liquids results from the retarded nonlinear optical response of the liquid molecules which includes a strong non-instantaneous contribution due to molecular reorientation. The nonlinear refractive index of the liquids is determined by fitting numerical simulations based on solving the generalized nonlinear Schrödinger equation including retarded response to the measured broadened output spectra. Our work is important for the novel field of near- and mid-IR supercontinuum generation in liquid-core optical fibers.