Research On The Sensing Characteristics Of Novel Optical Fiber Sensors Fabricated By Fusion Taper Technology

With the development of optical communication technology,a variety of optical fiber devices have been widely used in optical communication and optical sensing technology.Among many kinds of optical fiber devices,tapered optical fiber devices have important applications in optical fiber communication and optical fiber sensing technology.Therefore,they have been widely concerned and studied by scholars all over the world.The fabrication methods of tapered optical fiber devices have also been developed rapidly.At present,the main preparation methods of tapered optical fiber devices mainly include physical grinding and polishing,chemical etching,arc discharge heating,flame heating,and laser heating.In this paper,the self-developed electric heating fusion tapering system is used,and the ring-like graphite heating resistor is used as the heating source to prepare the tapered optical fiber device.During the tapering process,the heating power of graphite resistance,the movement direction of the displacement platform,the motion speed,and the motion time are all controlled by the tapering program to obtain the tapered fiber structure with different structural parameters.Combine multiple tapered fiber structures to obtain fiber sensors based on different principles,such as fiber gratings and fiber interferometers.According to the functional characteristics of different optical fiber sensors,the optical fiber sensors are used to measure physical parameters of the external environment such as refractive index,temperature and strain.This article firstly introduces the melting taper technology with different heating sources and compares the advantages and disadvantages of flame heating method and electric heating method.At the same time,it briefly introduces the electric melting taper system used in this article.The tapered fiber structure is introduced into the traditional multimode-single-mode-multimode structure by using an electrothermal fusion taper system,and the middle single-mode fiber is tapered to prepare a multimode-tapering single mode-multimode(MTSM)structure.The influence of the length of the multi-mode segment on its transmission spectrum is deeply studied.Simulation and experimental results show that for a fixed cone structure,as the length of the multimode fiber segment increases,the contrast ratio of interference peak of the transmission spectrum first increases and then decreases.For the measurement experiment of the refractive index sensing characteristic of the MTSM structure,when the refractive index of the external environment is 1.437,the refractive index sensitivity reaches the maximum of 1551.24 nm/RIU.In addition,temperature and strain sensing characteristic experiments were also carried out.The temperature experiment showed that the temperature sensitivity is-7.2 pm/? in the measurement range of 22.5?113.7 ?.The strain experiment shows that the maximum strain sensitivity reaches-9.2 pm/??.The characteristic of low temperature sensitivity effectively reduces the temperature-refractive index crosstalk problem.Secondly,the method of preparing the "flat taper" by the electrothermal fusion tapering technology is introduced,and the theoretical analysis and experimental verification are carried out.A "flat taper" is drawn at a same distance on single-mode fiber to prepare an ultra-long period fiber grating.With the aid of coupled-mode theory,the response formulas to refractive index,temperature,and strain of the ultra-long period fiber grating are derived,and its sensing characteristics are measured by experiments.The experimental results show that the refractive index sensitivity is-354.9 nm/RIU,the temperature sensitivity is 101.4 pm/?,and the strain sensitivity is-1 pm/??.Finally,a variable-diameter combined fiber grating is prepared.by periodically splicing multi-mode and single-mode fibers,and then using fiber diameter reducing technology to reduce the overall diameter to make it coupled.The sensor characteristic experiment is carried out,and the experimental measurement shows that the maximum refractive index sensitivity is 605 nm/RIU,the temperature sensitivity is 31 pm/?,and the strain sensitivity is 1.1 pm/??.In this paper,we used the method of fusion tapering based on the principle of optical fiber thermal deformation.It is an electric heating method with graphite thermal resistance as the heat source.Different tapered optical fiber devices is prepared by controlling the tapering process.Three types of optical fiber sensors based on tapered optical fiber devices are proposed.The optical characteristics of tapered optical fiber devices are used to realize the miniaturization of optical fiber sensors and improve the sensor sensitivity.