Research On Temperature Sensor Based On Optic-Fiber Interferometer

Temperature is closely related to today's social environment which is the most basic and important physical quantity.Therefore,measurement and control of temperature is of utmost important.Fiber-optic temperature sensors have received widespread attention from researchers due to the advantages of intrinsic safety,antielectromagnetic interference,easy distribution,and long-distance sensing compared with traditional temperature sensors.In particularly,the fiber-optic temperature sensor based on Sagnac loop and Fabry-Perot(F-P)cavity has also the advantage of resisting external vibration interference.However,the temperature sensor based on the Sagnac loop is limited by the low polarization coefficient of the fiber,and the length of the polarization fiber needs to be greatly increased to improve the temperature measurement sensitivity,so it is difficult to miniaturize the sensor head.While the temperature sensor based on F-P cavity is limited by the length of the cavity and it is also difficult to improve the sensitivity.Aiming at the problems of the above two types of optical fiber temperature sensors,this paper proposed hybrid cascaded interferencetype and dual-cavity cascaded interference-type optical fiber temperature sensors based on the Vernier effect.The specific research contents include:A fiber-optic temperature sensor based on cascaded Sagnac loop and F-P cavity was demonstrated and proposed.Firstly,we fabricated a F-P cavity based on single mode fiber-silica tube-single mode fiber(SMF-ST-SMF)by fusion splice,which length is 355 ?m.After that,fabricated a Sagnac loop by splicing a section of 2.49 m Panda fiber with SMF.Then cascaded Sagnac loop and F-P cavity to generate Vernier effect.Among them,the F-P cavity served as the reference cavity due to temperature insensitivity while the Sagnac loop served as the sensing loop.Experimental results show that the envelope appears when the Sagnac loop and F-P cavity are cascaded.The envelope shifts obviously when the temperature changed,and the sensitivity is-29 nm/? which is 20.7 times than that of single of Sagnac loop.Such a result is consistent with the theoretical calculations.Guaranteeing the condition that the length of the Panda fiber is not increased,the sensitivity of the sensor is increased by more than 20 times,and the problem of increasing the temperature sensitivity of the Sagnac loop lead to too long of the polarization fiber is solved.In addition,compared with a temperature sensor based on dual-Sagnac loop cascaded,the sensitivity of the sensor is significantly higher than the temperature sensor based on dual-Sagnac loop cascaded under the same interference spectrum magnification condition,and the sensor do not need to maintain constant temperature control due to the reference cavity is insensitive to temperature,which reduces the experimental difficulty.And it is more compact in structure than the double-Sagnac loop cascaded sensor.Two types of dual F-P cavity cascaded interference fiber-optic temperature sensors were proposed and prepared:First one,a fiber-optic temperature sensor based on SMF-ST-SMF dual-cavity.The sensor is made on the basis of a single air F-P cavity(333.68 ?m).The SMF at the end of the ST is cleaved into a preset length to form the third reflecting surface,thereby forming a silica cavity(218.29 ?m)matching the air cavity.Experiments were performed on this sensor.The temperature sensitivity is 183.99 pm/?,which is more than 200 times higher than the sensitivity of the single air F-P cavity,and 18.5 times higher than that of a single silica cavity,the result is consistent with theoretical analysis.Second one,a fiber-optic temperature sensor based on distilled water filled.An open cavity was fabricated by offset splicing a section of SMF between two section of SMFs(300.31 ?m).The cut the SMF at the end into a predetermined length to form a silica cavity(304.45 ?m)matching the open cavity.Finally,the open cavity is filled with distilled water and sealed in a ST.The experimental results show that the cascaded dual-cavity has generated Vernier effect,and the interference spectrum has a clear envelope.The interference spectrum envelope moves significantly when the temperature changes,and the sensitivity is 1.66 nm/?.Compared with the single cavity,the sensitivity is improved 11.1 times.