Research On Temperature Sensing Interrogation System Based On Fiber Bragg Grating In Optical And Microwave Domain

Optical fiber sensing is widely used in gas,water quality monitoring due to its light weight,high sensitivity,strong anti-interference and easy integration.Secondary pollution will not be induced to the environment even in the harsh environment of toxic,harmful,flammable and explosive.With environmental problems more severe and existing detection technologies' maturation,further need of fast,real-time,large-scale and simultaneous measurement for environmental indicators is increasingly urgent.In this background,a series of theoretical and experimental studies on novel fiber optic temperature sensing systems with light wave and microwave co-modulation are carried out in this paper.Different sensitivity can be achieved in different configurations.The outline of main work as follows.(1)Conventional fiber lasers with fixed bandwidth are poor in output power under saturation condition.It's difficult to meet with increasing system performance requirements,and the resolution of the sensors is also limited.A high power,narrow linewidth self-injection locked ring laser sensor is implemented in order to overcome the limitation.The change in the operating wavelength of the laser is converted into cavity length change.Within the temperature ranging from 26? to 36?,temperature changes is detected by measuring the laser output power through the oscilloscope.(2)A temperature sensing method based on microwave signal generation principle is proposed and verified by experiments.According to the principle,the fiber Bragg grating reflection spectrum can break the balance between the beat signals to convert the phase modulation into intensity modulation.The curve of the signal intensity and temperature is achieved in the experiment.The scheme can reflect the temperature tuning in the flat area of the amplitude response,which improves the sensing resolution near the center wavelength.The characteristic of the radio-frequency unbalanced M-Z interferometer for wavelength interrogation of the fiber Bragg grating(FBG)sensors is studied.The final output power of this RF-UMZI are measured in the experiment.According to the observation of a certain amount of samples for the output intensity at a specific microwave frequency,a peak recognition method applied for data points determination is proposed.This experiment is of practical reference value in performance improvement and feasibility study for incoherent light and microwave photonics filter utilizing in fiber sensing.