Research And Application Of Real-time Demodulation Technology For Fiber-optic Layer Fiber Interference Detection

It is especially important to realize precision exploration in Oil due to its strategic position of global economic and social development.In the petroleum detecting system of seismic wave which is widely used,optical fiber sensor(OFS)multiplexing network leads to the demand for high-speed real-time processing of mass data.Study of this subject is divided into two parts:design of the OFS network architecture and the realization of high-speed real-time data acquisition?processing and transmission.1.In order to satisfy the low cost and high performance requirements in the fiber-sensor-based underground oil detection system,a network architecture of the Michelson interference optical acceleration seismometer is designed.2.Then a real-time interferometric demodulation system is designed.Based on current difficulties that the traditional MCU or PC or other calculate platforms are difficult to be adapted to this requirement,EP3SE110F1152I3 FPGA of Altera Company is adopted as a real-time control and data processing core.The real-time interferometric demodulation system comprises the following parts:the time synchronization part-according to the accuracy requirement in time synchronization of the system,GPS receiver board from Hemisphere is adopted which can reach 20ns precision,and the communication between the GPS board and FPGA board is realized by RS232 serial port.The data acquisition part-it is realized by a high speed ADC chip from ADI Company which is configured by FPGA through Serial Peripheral Interface,based on this,a method to locate data in sampling window accurately is designed,then the intensity data of each sensor can be extracted in real time.The data processing part-in order to fulfill the phase unwrapping task rapidly in the fiber-sensor-based underground oil detection system whose signal frequency changes slowly(1Hz?200Hz),an phase calculation module based on the FPGA with high precision and high speed according to the region growing theory is given.This module includes the wrapped phase calculation module and the phase unwrapping module.Floating-point units and pipeline technology are adopted.The design of data synchronization based on FIFO is especially realized.The clock frequency can be up to 200MHz which denotes the number of retrieved phase per second is 2×108.Finally the communication part-it realizes the communication between the FPGA and the PC.The header of the data structure is designed to extract and process the data in framing module,then an USB2.0 chip is used to accomplish data communication with PC.The real-time interferometric demodulation system can realize the precision locating of sampling window,and realize the wrapped phase calculating and the phase unwrapping which is perfectly implemented in pipelined architecture based on FPGA,and the system can realize fast data transmission and processing.Through huge number of debugging and experiments on the platform of FPGA,we can come to a decision that the working performance is reliable,which manifest the real-time interferometric demodulation system can be served as a new solution in the optical-fiber-sensor-based underground oil detection system.