Developments Of Polymer Long Period Waveguide Grating Based Refractive Index Sensor

In recent years,to cope with the increasingly severe problems of water quality,food and drug safety,environmental pollution and to satisfy the needs of highly sensitive and low-cost miniature portable biochemical sensors,scientific researchers have studied the biochemical sensor in depth.As a research frontier in the field of sensor technology,optical biochemical sensor which has the advantages of high sensitivity,fast response and strong anti-electromagnetic interference has attracted wide attention as a promising sensor technique to work in high temperature,high humidity,flammable and explosive environment while traditional biochemical sensors cannot.Depending on the different detection principle and structure of the device,an optical sensor can be divided into two categories: label and label-free.Label optical biochemical sensor is likely to cause contamination during the calibrating process or affect the activity of the calibrator to interfere with the analysis results,besides,it needs longer testing time and expensive equipment.The label-free optical biochemical sensor avoids the interference of the calibrator to the sample and enables real-time on-line monitoring.The research of label-free optical biochemical sensors has focused on fiber biochemical sensors,optical flow control biochemical sensors and planar optical waveguide biochemical sensors.For the first time,this paper proposed a refractive index sensor based on polymer long-period waveguide grating which using the refractive index sensing liquid directly as its cladding layer,so that the sensor can work as a label-free sensor.Firstly,the research methods of optical waveguides,the coupled mode theory,and the working principle of long period waveguide gratings are discussed,especially the coupling between core mode and cladding mode.Secondly,aiming at the working characteristics of the polymer long-period waveguide grating refractive index sensor,the dispersion curve of the core layer transmission is analyzed,the single-mode transmission condition of the core waveguide is deduced,the coupling coefficient between core mode and cladding mode is calculated and the parameters such as the period and length of the long-period waveguide grating are determined.Next,the experimental samples were fabricated by UV exposure,development,magnetron sputtering and induction particle etching.Finally,based on the optical test platform,we launch the broadband light source as input light,change the refractive index of the liquid as the long-period grating cladding and detect the drift amount of the corresponding center wavelength in the output spectrum to obtain the transmission sensitivity of the sensor,the temperature sensitive characteristics of the sensor were also tested.The experimental results show that when the refractive index of the measured liquid changes by 0.002,the corresponding resonant center wavelength drifts 18.75 nm,and the sensing sensitivity of the device is 9375nm/RIU.Also for the temperature sensitive characteristics,the ambient temperature for each change 1?,the center of the resonant wavelength will move 1.47 nm for a fixed liquid to be measured.