Application Research Of Intermodal Interference Sensor In Security System

Optical fiber sensing shows many superiorities,such as stable performance,strong anti-electromagnetic interference capability,small size and light weight,making it become a hot-topic in the field of security.On the basis of the speed requirements of optic sensing systems for security monitoring field,we researched a fiber optic vibrator for short-distance and small-area zones,based on the principle of inter-mode interference of multimode fiber.The innovative work of the article is as follow:1.Analysis the application of fiber optic sensors,and the application of fiber optic vibration sensors in the field of security.Then introduced the principle of several fiber vibration sensing technologies.Theoretically analysis of the mode of multimode fiber,the principle of intermode interference and the elasto-optical effect.For the data processing and identification of fiber optic vibration sensors,theoretically introduce the filtering denoising method of wavelet transform and the feature extraction of wavelet packet energy spectrum,which provides theoretical basis for the experimental research.2.Based on the principle of inter mode interference,the single-mode multimode-single mode(SMS)optical fiber structure is applied to the optical fiber security system.In the system,multimode optical fiber is used as sensing fiber,combined with wavelet transform;realize the detection of external vibration signals.The theory of intermodal interference of multimode optical fiber is analyzed.The sensing optical fiber is arranged in the fence and laying on the ground,respectively.Experiment and analyses several vibration invasive events.The experimental results show that the sensing system of this structure can detect the vibration invasive signal quickly and effectively,it has good feasibility in the field of security in optical fiber.The structure sensing system maintains the advantages of simple structure,low-cost,which has very important significance in optical fiber security systems.3.On the basis of the vibration intrusion detection for the single-mode multi-mode single-mode(SMS)optical fiber structure sensor in the field of security.We propose a recognition method based on wavelet packet energy spectrum.The original vibration intrusion signal is extracted by the wavelet packet algorithm to extract the feature vector,and then select the first 8 frequency band partial eigenvectors with obvious signal characteristics.Then the acquired feature vectors are imported into the BP neural network algorithm to identify different intrusion signals.Through the experiment to obtain a lot of data to verify the identification of different vibration intrusion signals,the experimental results show that this method has more than 81% recognition efficiency for different intrusion events.It is an effective recognition method and can be used in practice.