Research On High Accuracy Distributed Fiber Sensor Based On Brillouin Gain Spectral Hole Burning Effect

Brillouin scattering distributed sensor can be applied to health monitoring of large infrastructures such as bridges,dams,tunnels,submarine cables and transmission lines.This kind of sensor use the linear relationship between Brillouin frequency shift and temperature/strain to measure,so the frequency resolution is an important index which determines the accuracy of the measurement,and the frequency resolution is inversely proportional to the Brillouin spectrum full width at the half maximum(FWHM).The FWHM obtained by the traditional Brillouin sensor is difficult to further reduce due to the influence of the phonon lifetime,which limits the performance of the sensor.In this paper,a sensing scheme based on Brillouin gain spectral hole burning effect is proposed.A narrow linewidth absorption peak is produced at the Brillouin gain spectrum resonance frequency,which improves the frequency resolution of the system,thus obtaining high accuracy of temperature and stress measurements.The main work of this article includes:1.A method for generating Brillouin gain hole burning is proposed.Two high power pulses which locate at the Stokes and the Anti-Stokes frequency of the continuous wave are used to interact in the optical fiber with the continuous wave,producing the coherent Brillouin gain and loss effect.Under the steady state,the hole burning spectrum with a linewidth less than 10 MHz is obtained in the fiber.2.The conditions of Brillouin gain hole burning effect are experimentally studied.The influence of pulse power,pulse width,continuous light power and fiber length on the excitation efficiency of Brillouin gain hole burning effect is analyzed.The experimental results show that the linewidth of the hole is inversely proportional to the pulse width,and the depth of the hole is directly proportional to the pulse power,the continuous light power and the length of the optical fiber.3.A temperature/stress distributed measurement based on Brillouin gain hole burning effect is realized.Using the hole burning spectrum of narrow linewidth at the Brillouin resonance frequency,the accuracy of the frequency measurement is two times higher than the traditional BOTDA.Therefore,the spectral hole burning represents a potential for improving the temperature/stress measurement accuracy of distributed Brillouin sensor.