Research On Liquid Refractive Index Sensor Based On Two-Mode Optical Waveguide Interferometer

As a sensing component in the internet of things system,sensors have important applications in the fields of scientific research,environmental monitoring,transportation,medical treatment,military and so on.However,many traditional sensors have been unable to meet a variety of new needs of people.It is urgent to research new sensing technology to realize the sensors with high sensitivity,easy to integrate and carry.The sensor based on two-mode waveguide(TMW)interferometer adopts single channel configuration,which has the advantages of simple structure,small size,low cost,easy integration and suitable for large-scale manufacturing.Especially since the sensing mode and the reference mode propagate in the same waveguide,the temperature and other environmental noise will act on both modes at the same time,thus avoiding the problem that the sensor is sensitive to the ambient temperature.In view of this,the liquid refractive index sensors based on the rectangular and the ridge TMW interferometer are studied in this dissertation,respectively.The polymer is used as the core material of the optical waveguide,and sucrose solution with different concentrations is used as the sensing analyte.The design,the fabrication process and the performance test of the proposed two sensors are systematically introduced.The main research contents of this dissertation are summarized as follows:(1)The research background and significance as well as the main types of optical waveguide biochemical sensors are introduced.The state of the art of the TMW interferometer sensors at home and abroad is reviewed.The fundamental of TMW interferometer is introduced,including the structure,the principle,and the mode solving method of rectangular waveguide.The theory of vanishing field sensing,and the principle and the characteristic parameters of the sensor based on the TMW interferometer are introduced.(2)The sensor based on the rectangular TMW interferometer is studied and then a sensor based on the ridge TMW interferometer is proposed.The specific research work includes: the relationship between the waveguide sensitivity and the waveguide parameters of the proposed two sensors are investigated,and then the dimensions of the used two types of waveguides are determined;the relationship between optical power distribution and spectral extinction ratio in the two-mode region is investigated,and the position of the single-mode waveguide with respective to the TMW is determined;the sensing performances of the proposed two sensors at different device parameters are investigated,and then the device parameters of the proposed two sensors are determined.The simulated results show that the designed rectangular and ridge TMW interferometer sensors can achieve the sensitivity of 3133 nm/RIU and 4933 nm/RIU,respectively.(3)The fabrication processes of the two types of TMW interferometer sensors are studied,the corresponding masks are designed,the fabrication of the devices are completed,and the sensing test platform is set up to evaluate the sensing performance of the fabricated devices.The results show that the sensors based on the rectangular TMW interferometer with different TMW widths exhibit the maximum sensitivity of 5240nm/RIU and the minimum sensitivity of 3073 nm/RIU,respectively.While the sensor based on the ridge TMW interferometer,when the widths of single-mode/two-mode waveguide widths is 1.9 μm/4.0 μm,the ridge width is 2.2 μm,and the ridge etching depth is 300 nm,the sensitivity of the sensor is 4630 nm/RIU,showing a significant improvement compared with the rectangular TMW interferometer sensor with similar size.