Design and application of high precision adjustable pulse unit in distributed optical fiber acoustic sensing system

Abstract

With the increasing application of distributed fiber acoustic sensing (DAS) technology in oil and gas resource detection, more attention has been attracted to the practicability and applicability of the DAS system. As an essential part of improving the system performance, the pulse signal generator unit has some problems such as high cost, single pulse parameters, and small range. In order to solve the issues mentioned above, an adjustable pulse unit applied in the DAS system is designed in this paper. The adjustable pulse unit takes the field programmable gate array (FPGA) chip as the hardware platform and keeps the variable frequency division technology and the pulse edge adjustment circuit as the critical module to generate the pulse signal with continuously adjustable pulse repetition rate, pulse width, and pulse edge. The host computer real-time controls the adjustable pulse unit to adjust the optical pulse parameters. The experimental results show that the adjustable pulse unit can achieve the functions of pulse width 5 ns ~ (1/pulse repetition frequency - 5ns), pulse repetition frequency 1 Hz ~ 50 MHz, and pulse edge 2.53 ns ~ 8.8 ns, which meet the requirements of the design. At last, the adjustable pulse unit applies to the DAS system. The results show that the adjustable pulse unit is well performed in the system, enabling the system to achieve high-quality vibration signal detection in positioning and restoring the external vibration signal. It proves the feasibility of the design scheme and achieves the expected effect. The design improves the flexibility and applicability of the DAS system in engineering applications.