Research Of The Sensitivity Adjustment Of Distributed Optical-fiber Safety Monitoring System

The safety of property is seriously threatened by the theft. According to the data from ICPO(International Criminal Police Organazition), the lost of museums caused by the theft of artwork and cultural objects is worth 4 to 6 thousand million dollars. The most terrible theft of bank in the Brazil led to a lost of 77 million dollars. The lost caused by indoor theft is more and more in our country. Therefore, it is important to develop a system which is suited to zone security. Optical fiber sensing system which combines fiber interference and fiber distributed sensing technology is one of the best technologies of zone security.New fiber interferometers were developed on the four basic fiber interferometers. Compare the new fiber interferometers with each other in 8 fields. According to the comparison, choose the signal fiber Sagnac interferometer as the prototype model. Rational analysis on the characters of waveguide of the 2×2 coupler, and on basis compare it with the 3×3 coupler. To rise the sensitivity of the system, use the 2×2 coupler to replace the 3×3 coupler. The polarization state of the light in the fiber will be changed when the fiber is disturbed or curved, and on the basis the intensity of the interference light will be changed. The change of the interference light will obstruct the judgement of the invasion. Discuss the polarization character of FRM( Faraday Rotating Mirror) from the base of Jones matrix. Design the optical path from the base of all above theory.Raise a presentation which achieve sensitivity adjustment of the system by changing the length of the delay loop, and introduce the modules of the system. Distributed fiber interference measure technology bases on the phase modulation. Basing on the principle of phase modulation, deduce the formula between sensitivity of the system and the length of the delay loop.Construct the experimental platform, and take experiment which includes four different kinds of disturbances. Day and night, take the experiment with four different delay loops. Using six different methods for processing experimental data collected, choose the best one for each disturbance and base monitoring and alarming invasion on its data. Designate the range of threshold according to the data collected for different disturbances and different delay loops. Prove that the sensitivity of the system can be changed by changing the length of the delay loop by analysing and comparing the data collected. Verify the formula deduced in the third chapter on the basis of data collected from the experiment, and analysis the reasons for the deviation between theory and experimental results.