Based Fiber Optic Distributed Sensing System Of The Phase-carrier Technology And Its Stability

With the development of the society, people's demands on security are growing higher and higher. Especially the security systems for the high-security sites are facing the test from the complex natural environment, which should be free from any weather, terrain and other environmental factors. On the other hand, with the expansion of the security and the modernization of the crime, we need a more comprehensive and wide-range security instruments and systems with low human error.Under this background, the distributed fiber positioning sensors are being researched as a new kind of distributed security systems. As the fiber has a wide working frequency, it could be measured easily. And as the fiber has high sensitivity, fast response, wide dynamic range and low transmission loss, it makes it possible to realize long-distance and multi-parameter monitoring. Meanwhile, the fiber is easy to bending and resistant to radiation, cauterization and explosion, which enable itself to be used in very hard environment.Based on the existing all-fiber distributed positioning system, this paper presents a brand new distributed all-fiber interference positioning system, which is based on phase generated carrier demodulation technology which increases the length of fiber-optic sensors. This paper also has some research on the stability of the system. Through simulation experiment, we show the positioning function of the system, and prove the ability of the system in enhancing the stability of the state of polarization functions.In this paper, the concrete work includes the following:By using lasers, phase modulators, couplers, the Faraday rotation mirror, photo detectors and optical devices, we create the all-fiber optical carrier phase distributed vibration sensor system with dual-interference optical path. The paper deduces the working principle of the system. When the vibration signal is imposed on the optical fiber, the vibration causes the change of the length and the index of refraction of the optical fiber, which leads the phase of the light in the optical fiber to change. The we use a interference optical path to switch the phase change to intensity change. After reverted by software, the phase shift of interferometric signals can be transformed into spectrum. There are series of periodic extremum in the additive power spectrum of vibration signals, and the position of the vibration signals can be determined by these extremal points. Using phase generated carrier techniques, carrying two carrier wave with different frequencies on the two sensing optic fiber, and demodulating these two signal in the signal-receiving port, than the double length of optic fiber cable can be inspected by single optic structure synchronously.In addition, the paper also makes a theoretical analysis of the stability of the system to prove that through the use of the Faraday rotation mirror instead of the commonly used coating light-reflecting mirror as the light-reflecting end could make the polarization state of the system insensitive, which greatly increases the stability of the system.Under the analysis of the working principle and stability of the system, it was proved that the validity of the phase demodulation arithmetic and positioning arithmetic through simulation signal and stampede signal experiments. And the contrast experiment with the all-fiber distributed positioning system which uses the light-reflecting mirror as the light-reflecting end proves the great increase of the stability of the system, which proves the practical value of the system.