Ultralong-distance Perimeter Fiber Pre-Warning System Based On The Combination Of φ-OTDR And MZI

In recent years, domestic and international security situation is becoming more and more serious. Pre-warning technology for long perimeter, such as airports, borderlines of our country, military bases and pipelines, get more and more attention due to the importance for infrastructure of national economy and defense system. This thesis focuses on the study of key techniques and devices for airport perimeter pre-warning system. The main works are achieved as the following.1. Based on the complementary advantages of combining cp-OTDR with Mach-Zehnder interferometer (MZI), an innovative fiber distributed disturbance sensor (FDDS) system was designed and setup to solve the high false alarm rate problem and simultaneous multi-point alarm problem. The major components in this system were determined.2. A F-doped dual-core photonic crystal fiber (PCF) with several circle holes array as modulation hole was proposed. By optimizing the structure parameters of this dual-core PCF, broadband and polarization insensitive coupling properties was achieved. Based on the proposed dual-core PCF, a ultra-broadband 3 dB coupler was realized. The variation of coupling ratio is within ±1% and coupling ratio difference between x-polarized and y-polarized mode is less than 2% in the wavelength range from 0.8μm to 1.7 μm. Compared with dual-core PCF with a central elliptical hole, the difficulty of fabrication of the proposed dual-core PCF can be lowered.3. Considering the existing problem in the FDDS system with the combination of φ-OTDR and MZI, we upgraded the hardware and software system and carried out outfield experimental test. The video camera and multimedia message send function was added in the FDDS system. The monitoring distance of FDDS system is up to 60 km and the resolution is not less than 50 m. By testing one hundred group data of outfield experiment, the successful recognition rates reached to 91.2%,88.3%,90% and 86.7%, respectively, for the four kinds of simulation disturbance pattern as percussion, climbing, watering and walking. The FDDS system has been installed for the perimeter of Zhangjiakou airport and get into the practical use.