Polydimethylsiloxane Based M-Z Interferometer Optical Fiber Sensor

Polydimethylsiloxane(PDMS,polydimethylsiloxane)has good hydrophobicity,high and low temperature resistance,corrosion and aging resistance,and so on.It also has low Young's modulus,high Poisson's ratio,elastic and transparent material.It's easy to cure,and it costs inferior characteristics.At the same time,PDMS,as a temperature-sensitive material,has good thermal expansion characteristics,and its refractive index changes with the temperature changing.It is a good fiber-optic sensing sensitive material.Based on the excellent characteristics of PDMS film in temperature sensing,this paper studies the performance of temperature sensing and hydrogen concentration sensing after combining PDMS film with optical fiber sensing structure.The main contents are as follows:1.Several typical optical fiber sensors are introduced:interferometric fiber sensors,including Mach-Zehnder(M-Z)interferometers,F-P interferometers,and Sagnac interferometers,special optical fiber sensors,which includes polarization-maintaining fibers,thin-core fibers,fiber grating.What's more,the characteristics of PDMS material are introduced in detail.2.An optical fiber temperature sensor based on a M-Z interferometer was proposed.The M-Z interferometer was fabricated by a fiber mismatch structure through core-offset fusion splicing method.It's coated with a PDMS film on its surface.The main principle of the sensing structure is to use the core mismatch.After the light enters the cladding,the cladding mode is excited,and the light of the core after recoupling occurs M-Z interference.When the ambient temperature changes,PDMS changes with temperature.The material's linear expansion due to heating and the thermo-optic effect cause its refractive index changing,which changes the output transmission spectrum.Therefore,temperature measurement can be achieved by monitoring the change in the resonance wavelength of the M-Z interferometer.The experimental results show that the proposed sensor has a temperature sensitivity of0.101 nm/°C in the temperature range from 20°C to 100°C.It is higher than the existing similar temperature fiber optic sensors,and the temperature measurement range is wider.3.A M-Z interference optical fiber temperature sensor based on bowknot-type taper structure was proposed.By setting the mode parameters of the optical fiber fusion splicer,the two segments of fiber are not fully connected.And during the process of electrical discharge fusion,a certain tensile force is applied to both ends of the optical fiber,and the cores of the fusion splicing are piled up into circular spheres to form an M-Z interference structure.When the temperature changes,the PDMS film on the sensor surface undergoes thermal linear expansion effect and thermo-optic effect,which causes the resonance wavelength to shift.Experiments show that the structure has a sensitivity of 0.212 nm/°C in the temperature range from 45°C to 120°C.The sensitivity is higher than the existing similar fiber optic sensors and the linear fitting coefficient is 99.134%.4.A bowknot-type taper structure M-Z interference optical fiber hydrogen sensor based on PDMS/WO₃ film was proposed.When hydrogen is in contact with the sensor,WO₃reacts with hydrogen and undergoes a redox reaction.After the heat released reaches the inner layer of the PDMS material,it undergoes linear expansion when heating,which results in a change in the transmission spectrum.The measurement of the hydrogen concentration can be achieved by monitoring the change in the resonance wavelength of the M-Z interferometer.Experiments show that as the hydrogen concentration rises from 0%to 0.701%,the light intensity at the resonance wavelength changes from approximately-18.9 d B to-21.1 d B,linearly shifts by a coefficient of99.832%,and the hydrogen concentration sensitivity reaches-3.1855 d B/%.