Investigation Of Distributed Optical Fiber Sensing Technology Based On Random Signal

The distributed optical fiber sensing technology,which uses optical fiber as the propagation medium and sensor,can monitor and measure the temporal and spatial change information of the optical fiber under test,and also obtain various physical parameters in the time and space domain.As a new distributed optical fiber detection technology,it has great development space in the fields of optical fiber communication network,building structure monitoring,environmental temperature measurement,security system maintenance,etc.The traditional distributed optical fiber sensing technology uses continuous light with sinusoidal frequency modulation or pulsed light as the detection,and it is difficult to trade off between sensing distance and spatial resolution.Physical random codes and chaotic laser are two typical random signals,which have the characteristics of wide frequency spectrum,noise-like,and auto-correlation curves of pushpin type.As distributed optical fiber sensor detection signals,they can overcome the above contradiction.Therefore,we propose a distributed temperature sensing scheme based on physical random codes and a distributed optical fiber fault break-point measurement scheme based on chaotic signal to achieve long-distance and high-precision distributed sensing.The main research works are as follows:(1)A Brillouin optical correlation domain analysis(BOCDA)technology based on physical random codes is proposed to perform a high-resolution distributed temperature sensing measurement,using the high-speed physical random codes generated by the autonomous Boolean network oscillator.First,the theoretical simulation model is established,and the feasibility of generating a high spatial resolution sensor with physical random codes is verified by numerical simulation.A 1 cm high spatial resolution is achieved through physical random codes with 10 Gbit/s code rate.Further,we set up an experimental platform: study the auto-correlation curve of the physical random codes,and the optical spectrum and frequency spectrum produced by the modulated light source.The BOCDA system based on physical random codes is built to implement distributed temperature sensing measurement.The research indicates that the code rate and extinction ratio of the physical random codes are the limiting factors of the spatial resolution and the sensing distance,respectively.Finally,a 3.9 cm spatial resolution temperature sensor is realized on a 1.1 km single-mode fiber,and the uncertainty of ± 1.1 MHz and the temperature coefficient of 1.15 MHz/? are obtained.(2)An optical time domain reflection technique based on the integrated chaotic laser is proposed to realize remote and high-precision fault break-point measurement.The time series of chaotic signal generated by the integrated chaotic source exhibits a certain degree of oscillation and random fluctuations.Its auto-correlation curve shows typical chaotic state characteristics,with the full width at half maximum of 0.1 ns.The standard power spectrum bandwidth of 5 GHz is obtained.We first verified the spatial resolution of the system and obtained a spatial resolution of 1 cm,then multiple single reflection events and a dual-reflection event 10 cm apart were measured,and the spatial resolutions of 0,5,11,21,27,50,61,and 76 km fiber fault points were analyzed.Finally,the spatial resolution and range-independent breakpoints measurement has been realized,and the detection range of 76.54 km and the spatial resolution of 1 cm(7.7 million resolved points)have been experimentally demonstrated.