Research Of Measuring Pulling Quantum In Long Distance Fibers

The landslides have become one of the most common geological disasters in many mountainous areas of China.Every year,landslides cause much injuries and economic losses.So monitoring the state of the region which exist the risk of landslides is becoming more and more important.The accuracy of traditional monitoring technology exist much shortage,because it is often influenced by the harsh environment of landslide monitoring,electromagnetic interference,the change of temperature,the purchase cost,the power supply and energy consumption in long distance monitoring.Faced with the problem of monitoring landslide,it needs a set of low-cost low-power supplied distance measuring system which is suitable for the complex geographical environment and little influenced by electromagnetic interference.Combined with the basic principle of wavelength division multiplex(WDM)distributed Fiber Bragg Grating(FBG)wavelength shift in measuring strain and the function of detecting phase difference by using AD8302 circuit,this paper proposes an optical fiber detecting distance sensing system by the means of indirectly measuring the phase difference between pulse signals of equal time interval.We add amplitude modulation on the 1550 nm light source with the interval sinusoidal pulse signal,and analysis and research the relationship of the phase difference in two interval sinusoidal pulse signals of different parameters and the output voltage of the AD8302 circuit.In the process of measuring fibers-train by detecting phase difference between pulse signals of equal time interval,three kinds of phase difference detection schemes are designed and implemented.One scheme is the combination of electrical signal and transmitted light signal in the transmission system,one scheme is the combination of two optical signals in the transmission system,and the rest one is the combination of two reflected optical signals in the reflection system.In the final reflection,Fiber micromachining structure in a certain reflectivity is made up.After the detecting phase difference scheme is designed,the signal generator module,the whole optical path designed module and the detecting phase difference module are designed and built,the experimental data on the measurement of the strain of the optical fiber displacement in these detecting phase difference are tested and evaluated.In the scheme of the combination of electrical signal and transmitted light signal in the transmission system and the scheme of the combination of two optical signals in the transmission system,we not only have got a better measured data,but also got a certain accuracy class for practical engineering needs.The errors of these scheme are ±4.44 mm and ±2.02 mm respectively.In the scheme of the combination of two reflected optical signals in the reflection system,The results of certain validity measurements were obtained,and every error factors affecting the results measured are analyzed,so that it can be used for providing the feasible direction in how to get the strain length information from the reflected light which is modulated.The three system for measuring the strain length by detecting the phase difference provide a constructive technical support for obtaining the fiber strain length system with lower cost and less affected by the complex monitoring environment.