DISTRIBUTED OPTICAL FIBER SENSOR FOR LONG-DISTANCE OIL PIPELINE HEALTH

A fully distributed optical fiber sensor (DOFS) for monitoring long-distance oil pipeline health is proposed based on optical time domain reflectometry (OTDR). A smart and sensitive optical fiber cable is installed along the pipeline acting as a sensor. The experiments show that the cable swells when exposed to oil and induced additional bending losses inside the fiber, and the optical attenuation of the fiber coated by a thin skin with periodical hardness is sensitive to deformation and vibration caused by oil leakage, tampering, or mechanical impact. The region where the additional attenuation occurred is detected and located by DOFS based on OTDR, the types of pipeline accidents are identified according to the characteristics of transmitted optical power received by an optical power meter. Another prototype of DOFS based on a forward traveling frequency-modulated continuous-wave (FMCW) is also proposed to monitor pipeline. The advantages and disadvantages of DOFSs based on OTDR and FMCW are discussed. The experiments show that DOFSs are capable of detecting and locating distant oil pipeline leakages and damages in real time with an estimated precision of ten meters over tens of kilometers.     

NOVEL FIBER GRATING SENSOR DEMODULATION TECHNIQUE BASED ON OPTICAL WAVELET FILTERING

The optical wavelet filter is designed. It can filter and choose frequency swiftly. It can realize demodulation of distributed fiber Bragg grating(FBG) measurement system. Its scanning resolution and scanning period depend on wavelet function. Wavelet function is controlled by computer. Compared to conventional scan filter, optical wavelet filtering has some advantages such as simple structure, high scan frequency, high resolution and good linearity. At last, the error of optical wavelet filter scanning procedure is analyzed. Scanning step length refers to the shifting of optical wavelet window's central frequency. It affects system precision directly. If scanning step length is different, the measured signal is different. The methods of reducing step length guarantee scanning periodic time are presented.     

AN OPTICAL FIBER TEMPERATURE SENSOR BASED ON AN ETHANOL FILLED FABRY-PEROT CAVITY

Optical fiber Fabry-Perot interferometers have been widely used as sensors. A novel anhydrous ethanol-filled optical fiber Fabry-Perot temperature sensor was reported in this article. Based on the characteristics of the temperature-controlling refractive index, the ethanol may serve as a sensitive medium for a sensor. According to the experimental results, the refractive index of the ethanol was changed by approximately 0.02617 when the temperature increased from 16°C to 74°C. A cavity length of 94 μm was used to demonstrate the feasibility of this sensor. The resonance wavelength of the sensor shifted about ?0.42 nm/°C. The novel optical fiber Fabry-Perot temperature sensor was simple, compact, sensitive, and immune to electromagnetic interferences.     

光纤端面研磨加工的表面质量

研究光纤端面研磨时高质量表面的形成机理已成为提高光纤连接器质量和制造效率的重要课题。选用粒度为0．5-6．0μm金刚石磨料砂纸,在KE-OFP-12型光纤连接器研磨机上对光纤端面进行研磨,发现光纤研磨加工存在脆性断裂、半脆性半延性和延性等三种材料去除模式,且材料去除模式主要由磨料粒度控制,磨料粒度为3μm 时,为其脆延转换的临界点,并从理论上对其进行了分析。试验证明以延性去除得到的光纤表面粗糙度远低于以脆性断裂去除得到的表面粗糙度,是提高光纤研磨表面质量的有效途径。光纤以延性模式研磨加工时,光纤表面粗糙度可达到5nm,其表面看不到任何划痕,可使光纤连接器的插入损耗及回波损耗等光学性能满足高速、宽带光纤通信的要求。     

IMPROVED SENSITIVITY OF A PHOTONIC CRYSTAL FIBER EVANESCENT-WAVE GAS SENSOR

An evanescent-wave absorption gas sensing theory and technique is demonstrated using a solid-core photonic crystal fiber (PCF). This article proposes and demonstrates the theory and method of gas sensing based on the PCF evanescent-wave. Numerical simulations and systematic analysis were conducted regarding the influence of PCF structure parameters to its light transmission characteristics, dispersion characteristics, and loss characteristics. Based on these results, this article puts forward and designs the overall schematic of a gas sensing system with the PCF as the gas chamber. Through numerical simulation, the influence of the relative sensitivity of the gas measurement system caused by PCF structure parameters is analyzed, and a design for PCF is proposed with optimum geometric structure parameters.     

A NOVEL ALL-FIBER ELECTRIC FIELD SENSOR BASED ON TAPERED FIBER-SLAB WAVEGUIDE COUPLER

□ A novel optical electric field sensor based on evanescent coupling between a tapered fiber and a slab waveguide is proposed and demonstrated. Light in a tapered fiber evanescently couples into the slab waveguide and forms a wavelength resonant spectrum. A slice of a LiNbO₃ crystal was used as the slab waveguide. External electric fields may change the refractive index of the crystal and thus make the resonant wavelengths shift. Therefore, an optical electric field sensor was obtained by measuring the wavelength shift caused by an external electric field. The principles and design of the proposed sensor are reported. The performance of the proposed sensor are demonstrated experimentally by detecting sinusoidal fields with 50 Hz and pulsed electric fields with a rise time of 1.2µs. The results show that the minimal detectable field was approximately 150 V/cm with a signal-to-noise ratio of three.     

全光纤硅谐振传感器关键技术的研究

光源激励和光信号检测,是全光纤硅谐振传感器的两项关键技术。通过研究,成功地解决了光源激励中输出功率、波形、恒流工作和宽频带等技术问题。根据相关检测原理设计的检测电路,成功地实现了对微弱光信号的检测,并具有很高的动态响应。