Study On Microfluidic Long Period Side Hole Fiber Grating Sensor

In 1988,researchers found that the birefringence of Side-Hole Fibers?SHF?will be af-fected by pressure,so SHF were mostly used as optical fiber pressure sensors in the early years.In recent 30 years,SHF sensing has made tremendous progress,from pressure sensing,temperature sensing and stress sensing,to the present magnetic field sensing,electric field sensing and so on.There are two symmetrical circular holes around the core in a SHF,and its size is in the order of micron.It is suitable for microfludic optical fiber sensor.Unlike pho-tonic crystal fibers,only two microholes included in a SHF,which are relatively large in size and easy to control microfluidics samples.In this dissertation,theoretical and experimental research on microfluidic SHF sensor was carried out.The main work is dividing into the fol-lowing aspects:Firstly,the birefringence composition of SHF and the principle of LPFG were analyzed.The geometric birefringence and stress birefringence were analyzed by numerical method and finite element method respectively,and the relationship between the fiber shape and the bire-fringence is studied.In the LPFG part,the transmission spectrum of LPFG and the influence of various factors on grating spectrum were analyzed by coupling mode theory.Secondly,series LPFG with periods of 480 and 500?m respectively was fabricated in SHF by CO₂ laser.The structure of FBG was encapsulated by quartz tube,and the real-time replacement and measurement of microfluidic samples were realized.Temperature and refrac-tive index were measured respectively in the experiment,and the simultaneous measurement of temperature and refractive index was realized.Finally,a long-period SHF grating was fabricated by twist method.The grating period is500?m and the resonance wavelength is 1535.44 nm.The dual-channel measurement of the microfluidic chip was realized by combining the grating with the microfluidic chip.This kind of sensor has high refractive index sensitivity.In this dissertation,a microfluidic long-period fiber grating?LPFG?sensor based on SHF was investigated.Two kinds of microfluidic sensors were fabricated using SHF:serial LPFG microfluidic sensor and twisted LPFG microfluidic sensor.CO₂ laser was used for writing double LPFG in SHF,this kind of series LPFG microfluidic sensor realizing simultaneous measurement of temperature and refractive index.Microfluidic twisted LPFG sensors was fabricated by twisting the SHF in melting state,which improves the sensitivity of refractive index and realizes the measurement of double microfluidic channels.This kind of SHF sensor could be used in many microfluidic detection occasions.