Research On Optical Fiber Pressure Sensing Based On Wavelength Demodulatio

Sensing technology as one of the three pillars of modern information technology,its development level represents a country’s informatization level.Sensors can be used to monitor pressure,temperature,humidity,strain and other parameters in real time in engineering applications,which also widely used in industrial production,space development,ocean exploration,environmental protection,resource investigation,medical diagnosis,biological engineering,even cultural relic protection and other extremely wide range of fields.Moreover,optical fiber pressure sensor is a kind of sensor which commonly used in industrial applications,when the external minor pressure is applied to the optical fiber,the changes of the phase,intensity,polarization and other characteristics of the optical spectrum for the sensing system caused by the changes of refractive index and length of the optical fiber.By detecting the characteristic parameters of the changes,the detection of external pressure changes is realized.Optical fiber pressure sensor has the advantages of small size,light weight,high sensitivity,anti-electromagnetic interference,corrosion resistance,etc.,so it has a wide range of application prospect.Optical fiber pressure sensing technology based on phase modulation has the advantages of high detection sensitivity,flexible optical path,and wide range of measurable objects.On the basis of previous research,this paper focuses on the in-depth study of the optical fiber pressure sensing technology based on wavelength demodulation.The main research contents are:First,by comparison the demodulation methods such as intensity demodulation,phase demodulation and wavelength demodulation method,the wavelength demodulation method is selected as the signal demodulation method for the subsequent sensing experiments in this paper after comprehensive consideration.Second,a temperature sensing system with low cost,simple structure and easy operation is proposed,which based on the characteristics of narrowband and temperature sensitive of the π-phase shift fiber grating(π-FBG).The experimental results show that the wavelength of π-FBG linearly changes with the increase of temperature,the linear fitting degree is 0.9995,and the temperature sensitivity is about 10.2 pm /°C.Third,based on the birefringence characteristics of polarization-maintaining fiber(PMF)and the interference principle of Sagnac interferometer,a fiber pressure measurement sensor system based on PMF-Sagnac ring structure is proposed.The system with a simple structure,low cost and easy operation.Theoretical analysis shows that there is a linear relationship between the wavelength shift and the changes of pressure.The experiment verifies the characteristics of pressure sensing with the length of the sensor probe is 1 m and 2 m,respectively.The experimental results show that with the increase of pressure,the wavelength of the sensing system changes linearly,the linearity is 0.998 and 0.995,respectively.Meanwhile,the sensitivity is0.258 nm/N and 0.133 nm/N,respectively.And with the length increasing of sensing fiber,the 3 d B bandwidth of the transmission spectrum trough remain constant.Fourth,a fiber laser pressure sensing system based on the cascaded Mach-Zehnder and Sagnac structure with unequal arms is proposed.The transmission characteristics of the sensing system are analyzed by using the transmission matrix theory,and the expression between the output spectrum and the phase difference is deduced.The output spectrum of the cascaded filter structure and the laser sensing system was analyzed by simulation.The experimental results show that the-3 d B bandwidth of the reflection interference peak generated by the proposed system is less than 0.02 nm,and the signal-to-noise ratio can exceed 45 d B.When the length of the sensor head is 1 m,the pressure sensitivity of the sensing system is 29.275 nm/MPa,and the interference spectrum of the sensing system fluctuates less than ±0.02 nm within 1 hour.Therefore,the proposed sensing system possesses attractive properties such as good sensing linearity and stability,high signal-to-noise ratio,and high sensitivity.