Research On Daul-parameter Measuring Sensor Based On Special Optical Fiber And Spherical Structure

As an important part of the sensing field,optical fiber sensors have many advantages compared with other types of sensors,such as anti-electromagnetic interference,corrosion resistance,high sensitivity and remote sensing.Among them,the Mach-Zehnder(M-Z)interferometer fiber optic sensor uses one optical fiber to complete the sensing measurement,which is compact,simple production,and has been widely studied and applied.Based on the previous researches of M-Z interferometric fiber sensors,the new-type dual-parameter optical fiber sensor using the special optical fiber and spherical structure have been fabricated in this paper.1.A dual-parameter interferometric optical fiber sensing structure based on thin core fiber(TCF)and the spherical structure is designed.The TCF is welded between two spherical structures made by single-mode fiber(SMF).Through simulating analysis of Rsoft software and experimental research,the spherical structure effectively excites the cladding modes of TCF.The sensor can re-couple the mode and output the interference spectrum.Since the two selected dips exhibit different wavelength shifts,the temperature and the refractive index can be measured simultaneously.Measured sensitivity of temperature are 0.067nm/ ? and0.050nm/ ?,respectively.Sensitivity of refractive index are-69.71nm/RIU and-119.9nm/RIU,respectively.The sensitivity coefficient matrix can be used to realize simultaneous measurement of temperature and refractive index.2.An optical sensor for simultaneous measurement of temperature and refractive index is proposed theoretically and demonstrated experimentally.It consists of a special type of fiber-few mode fiber(FMF)welded in the two spherical structures.The two spherical structures act as couplers that can excite the cladding modes and couple the cladding modes back into the core.Two interfering dips of different sensitivities are selected,the shift of the wavelength is recorded,and the simultaneous measurement of temperature and temperature is performed by using the sensitivity coefficient matrix.The temperature sensitivity is achieved at 0.054nm/?in the temperature range of 25 ? to 80 ? and the refractive index sensitivity is-27.77nm/RIU in the variation range of 1.335 to 1.398.3.Aiming at FMF,a simple sensing structure based on SMF-FMF-SMF has been fabricated and analyzed experimentally and theoretically.Based on its low sensitivity,a dual-parameter fiber optic sensors based on the FMF with two down tapers is fabricated.Due to the sudden drop in fiber diameter,the tapers increase the evanescent field around the clad of optical fiber and make the sensor more sensitive to changes in the surrounding environment.The measured sensitivities of temperature are 0.097nm/? and 0.114nm/?,respectively,and the sensitivities of the refractive index are-108.07nm/RIU and-97.43nm/RIU,respectively.By comparing the theoretical simulating and experimental results of these two sensingstructures,the sensitive performance of sensor based on FMF with two tapers is improved significantly.