Raman Distributed Temperature Sensor Based On Pulse-Coding Technique

RDTS(Raman distributed temperature sensor)is a kind of temperature sensor based on Raman effect in optical fiber.For RDTS,there are some distinguished advantages such as high dynamic range,less sensitivity to strain.As a branch of optical fiber sensing technology,RDTS is widely used in many important industrial applications such as fire detecting in oil and gas pipeline,temperature controlling in power plant and power transmission line and leakage detecting in embankment dams.For these applications,the performance of RDTS is widely attracting attentions.Besides,many methods and system structure for improving RDTS system performance are developed according to different industrial application scenes.Among these techniques,pulse coding technique has been paying more attentions since it is able to increase the system SNR(signal-to-noise ratio)while keeping the same spatial resolution.However,for the application of coding technique in long-range system,there are still many problems to solve.In a word,we can find great potentials of applications and theoretical significance by conducting research on this technique.In this paper,first,the theoretical analysis and mathematical modeling of RDTS under single pulse input are carried out,and simulations are performed by using software.Based on this,the principle of improving RDTS performance by Simplex coding is analyzed,and the corresponding simulation model is established.According to the simulation above,considering the limitation that the pulse code sequence is amplified by EDFA(erbium-doped fiber amplifier),the new dual-source RDTS configuration based on pulse coding is proposed and the optical/electrical system is established following the perspective of cost-effectiveness.The construction and performance measurement,compared with the traditional RDTS system,shows the advantages of low cost and long sensing distance.In this paper,two DFB(distributed feedback)laser diodes are used as the light source.The new direct modulation scheme avoids the use of modulators and drivers and thus reduces system cost.At the same time,through the cooperation between the two light sources,the transient effect generated by the EDFA in amplifying the encoded signal in the long distance is eliminated,so that the system can combine the EDFA amplification and the Simplex coding to improve the performance.Different from traditional NRZ(non-return-to-zero)Simplex encoding,the system uses RZ(return-tozero)Simplex encoding to further increase the peak power of the incident pulse to achieve a sensing distance of up to 56 km.