Fast BOTDA For Dynamic Strain Measurement Based On High-Order Side-Bands By Injection-Locked Laser

The measurement of dynamic sensing plays an important role in the safety monitoring of buildings and roads,national defense and military,etc.Optical fiber sensing technology has unique advantages in dynamic measurement.Optical fiber is used as a sensing tool and information transmission tool.The system is small in size,easy to lay,high sensitivity,and anti-electromagnetic interference.Brillouin optical time domain analysis technology is one of the most typical technologies in optical fiber sensing systems.Based on the stimulated Brillouin scattering effect,the system has a high signalto-noise ratio and high spatial resolution,which has great research value.The traditional BOTDA system has a long measurement time and cannot measure rapid changes.Dynamic BOTDA requires a relatively large bandwidth for microwave generators and other microwave devices,usually around 11 GHz,which will greatly increase the system cost.In response to this problem,this subject proposes a dynamic BOTDA system that can greatly reduce the bandwidth of microwave devices,can achieve dynamic measurement,is feasible,and has low cost.The research content is as follows:Firstly,set up a traditional BOTDA system and use the principle of optical injection locking to propose different injection locking schemes: amplify high-order sidebands by injection locking first-order sidebands and direct injection-locking high-order sidebands.Through the Brillouin spectroscopy measurement experiment and analysis of different locking schemes.Secondly,make improvements on the basis of the BOTDA system,increase the intensity of microwave modulation,and build a frequency agile BOTDA system.Using intensity modulation and phase modulation two modulation methods,compare the characteristics of the two schemes in the static tensile test,and measure the stress coefficient.Finally,two modulation methods are used for dynamic measurement.First,an axial electric displacement platform is used to dynamically stretch the optical fiber,and the fast measurement mode of the oscilloscope is used to measure the uniform speed during the stretching process.Intensity modulation can be used to reduce the microwave frequency from 11 GHz to 1.2 GHz using the ninth-order sideband,and the phase modulation method can be reduced from 11 GHz to 1.5 GHz using the seventh-order sideband.The fifth,seventh,and ninth-order sidebands of the intensity modulation scheme are selected for dynamic vibration measurement at 12 Hz,17.3 Hz,and 14.8 Hz.