Study On High-speed Demodulation System Of Fiber Fabry-Perot Based On Dual-LED

Test technique is tied with the design,material process for one of the three main techniques in aero-engine research and development.It is an important foundation for establishing and perfecting engine design theory and simulation calculation models,an effective way to evaluate new structures,as well as a necessary means to verify the performance,reliability,and durability required for engine use.The fluctuating pressure generated by the hot air in the engine combustion chamber can be used to characterize the stability of the air flow field in the engine,and large variations in fluctuating pressure can lead to internal instability and even disastrous engine failures.And the use of traditional mechanical and electrical pressure sensors is limited,because the aero-engine always works in the environment of high temperature,high pressure and strong electromagnetic interference.Therefore,it is of great significance to research on a new type of sensing system that can work in a complex environment and realize the monitoring of the fluctuating pressure inside the engine for analyzing the state of the combustion chamber and evaluating the safety of the engine.With the advantages of small size,high temperature and high pressure resistance,strong electromagnetic interference resistance,the fiber Fabry-Perot sensor can realize in-situ measurement of the measured object and improve the measurement accuracy.Therefore,the sensor can directly measure the fluctuating pressure of combustion chamber.Since the fluctuating pressure of combustion chamber has the characteristic of high frequency,the sensor needs to have a high response frequency,and the demodulation system is also required to have the characteristics of high speed and large range.Therefore,this paper proposes a dual-LED demodulation system based on fiber Fabry-Perot sensor,which can realize demodulation with large range and high speed.The research design of the whole demodulation system includes the design of optical system and the design of hardware acquisition circuit.Firstly,the theoretical model of dual-LED demodulation system was derived and established,and the demodulation characteristics were analyzed according to the theoretical model in this paper.Based on the theoretical model,the optical structure in the demodulation system were further designed,including the structure design of the interferometer and the selection of the central wavelength and bandwidth of the light source.Next,the hardware acquisition circuit was designed,including the design of the circuit,the driving logic and the upper computer.Finally,the assembly and debugging,parameter calibration and demodulation performance test of the dual-LED demodulation system were completed.The range,resolution and stability of the demodulation system were tested and analyzed in this paper.The test result shows that the dual-LED demodulation system designed in this paper has a good working stability.The measurement of the cavity length is realized within the theoretical range(4.74μm),and the resolution of the cavity length is about 5nm.In addition,the nanosecond switching speed of LED and the use of singlepoint detector can achieve high-speed demodulation.