| Optical fiber sensing has a wide range of applications such as physical,biochemical fields and so on owing it has the characteristics of rapid response,efficient security and simple use.Polarization-maintaining fiber can be used as high-quality sensor material because of its high birefringence and low polarization dispersion.Compared with other interference principles,Mach-Zehnder is more suitable for optical interference sensing since its simple and stable characteristics.The research focus of this paper is based on the Mach-Zehnder interference principle.Three different mode interference structures are designed and fabricated in the experiment by utilizing polarization-maintaining fiber.Meanwhile,we have discussed the theory of mode interference for the structures.Based on this principle,sensing measurements and property analysis are performed on the physical quantity such as temperature,strain,and refractive index.The main research contents include the following aspects:?1?A dual up-taper structure is designed by utilizing polarization-maintaining fiber to realize temperature and refractive index sensing measurement.The theoretical temperature sensitivity expression is established based on the polarization-maintaining fiber mode interference theory,and the feasibility of the theory is demonstrated through the actual temperature sensing experiment.The optimized structure is used for the refractive index sensing experiment,and the refractive index sensing sensitivity of168.73 d B/RIU and 17.656 nm/RIU are obtained in the experiment.?2?An up-down taper structure is designed,and the superimposed evanescent field effect is used to improve the sensitivity of the refractive index sensor.Experiments show that the sensitivities can reach 310.40d B/RIU and 34.2545nm/RIU,respectively.It is higher than most light intensity modulation type refractive index sensors.The cross-talk caused by ambient temperature changes in this structure is less than1.4×10-4.?3?An optimized dual down-taper fiber structure is designed to achieve simultaneous strain and temperature measurement.The influence of the spherical core which is located at the middle of the down-taper to the extinction ratio of the transmission spectrum is analyzed.Compared with the dual down-taper structure under the same parameters,this structure can obtain a larger extinction ratio and lower transmission loss.Experiments show that the strain and temperature sensitivity of the proposed structure are 37.13pm/??and 75.34pm/?,respectively.The relative errors of strain and temperature measurement are less than 1×10-3%,which provides a new scheme for the simultaneous measurement of strain and temperature. |
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