| The fiber Fabry-Perot sensor has the advantages of high sensitivity,small in size and good long-term stability.It is suitable for the health monitoring of large structures such as bridges and dams.For large-scale equipment such as aircraft engines,nuclear powered engines usually work under situation of high temperature and high pressure,its structural health monitoring requires fiber F-P sensor system has higher accuracy and reliability.The non-scanning correlation demodulation method utilizes an optical wedge to realize correlation demodulation.There is no movable part,and the stability is good.It is a widely used demodulation method for fiber Fabry-Perot sensors.However,in order to meet the more stringent monitoring requirements for large-scale equipment,It is still necessary to study the influence of key components on demodulation accuracy from the principle.In this paper,based on the principle of non-scanning correlative demodulation system,the influence of key components such as light source,demodulation optical path and optical wedge on the demodulation signal is investigated.A reflective non-scanning correlative demodulation system is designed and built and the related experimental research has been carried out.It includes the following several aspects:(1)The effect of light source on demodulation signal is studied.According to the optical principle of non-scanning correlative demodulation system,the influence of bandwidth and center wavelength of light source on demodulation signal is analyzed.In order to analyze the influence of light source,the SLD with a central wavelength of 980 nm and the LED with a center wavelength of 520 nm are selected as the system light sources.(2)The effect of optical path on demodulation signal is studied.The influence of the light distribution on the demodulation signal is analyzed,and the influence of light incident of optical wedge on the contrast of signal is discussed.In order to make effective use of light distribution and improve signal contrast,a demodulation optical path based on freeform surface mirrors is proposed.(3)The effect of optical wedge on demodulation signal is studied.A mathematical model of optical wedge is established,the influence of non-uniform thickness and surface albedo of air wedge on the demodulated signal is analyzed.A compensation method that can reduce the demodulation error caused by air wedge is derived.The manufacture,detection and evaluation methods of optical wedge are given.(4)Experimental research.A non-scanning correlative demodulation system is set up.The cavity length demodulation of fiber F-P sensors is carried out under the condition of different light sources and different optical wedges.The experimental results show that when input optical power of LED is 6 times lower than the SLD,the demodulation accuracy is still better than SLD.It is indicated that using short center wavelength light source is conductive to improving the demodulation accuracy.The non-uniformity of air wedge thickness has a great influence on the demodulation accuracy,and the measurement error can be reduced by compensation method. |
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