Research On Sensing Properties Of High Sensitivity Optical Fiber Coupler With Tail Ring

Being a noval sensor device,optical fiber sensors have the unique advantages of antielectromagnetic interference,high sensitivity and easy integration.The fiber coupler is a common passive optical device that can be used not only as an optical connection device but also as an optical sensor element.Due to its various functions,the fiber coupler has received much attention from researchers in different fields.It has become an important member of optical device.A novel optical fiber coupler with a tail ring is proposed in this thesis,which can realize a two-parameter measurement for refractive index and temperature.The affecting factors on sensing performance and the several sensing solutions proposed are analyzed in the theoretical and experimental.The corresponding advantages and disadvantages are analyzed and compared.Combining the different characteristics of the fiber coupler into a sensor for the sensing temperature and salt in the marine environment has a great potential practical value.The main contents are listed as follows:(1)The development status of optical coupler in the field of optical sensing and the advantages and disadvantages of the fabrication methods of optical fiber coupler are summarized.A novel optical fiber coupler with a tail ring is proposed by combining the optical sensing characteristics and optical connection characteristics to achieve the two-parameter measurement.(2)According to the application of mode coupling theory in fiber coupler,the influence of relevant parameters of fiber coupler on the sensing performance is studied.Some performance indexes and the sensing principle of fiber coupler are analyzed,which provides theoretical guidance for the sensing experiments later.(3)According to the proposed sensing structure the simulation software was used to simulate the structural parameters of the optical fiber coupler.The influence of different parameters in the fiber coupler on the performance of the fiber coupler was analyzed.Based on the flame-stretching method,the fiber copler with a tail ring was fabricated.Then the refractive index sensing experiments of the fiber coupler in coupling region were carried out.The performance of the sensor is analyzed according to the experimental results,and a high sensitivity is achieved in the range of 1.33 to 1.3535.By optimizing parameters of the fiber coupler,the sensitivity of 11780.5 nm/RIU can be achieved.(4)Combined with the proposed optical fiber coupler with a tail-ring sensing structure,three different tail-ring temperature measurement schemes are proposed to realize temperature sensing measurement.Their temperature sensing performance is analyzed based on the experimental results.Besides,the advantages and disadvantages of each method are analyzedIn this paper,the proposed optical fiber coupler with a tail ring is used to achieve highsensitivity refractive index sensing in the range of 1.33?1.3535.Through the design of the sensing structure of the tail ring portion,the two-parameter measurement of temperature and refractive index is realized together with the coupling region of the optical fiber coupler.