Simultaneous Measurement Of Refractive Index And Temperature Based On HiBi Fiber Loop Mirror And Multimode Interference

Accurate and in-situ monitoring of the refractive index of liquids is important for chemical and biological sensing in medical,industrial and environmental applications.But due to the temperature-RI crosstalk,some of the measurement results for refractive index were unreliable.To solve this problem,a lot of works have been done so far.Fiber optic sensors,in particular,presented an excellent solution in this context due to their feasible integration to other fiber optics components,high sensitivity,small size,and capability for in-situ,real-time,remote,and distributed sensing.HiBi-FLM was interesting devices that usually consisted on a section of HiBi fiber that is spliced between the output ports of a directional optical coupler.Independence of input polarition and insensitivity to perturbations in the lead in fibers were some of its most attractive features.And it has been demonstrated for numerous applications especially for the measurement of physical parameters and due its high temperature sensitivity,HiBi-FLM was also presented for temperature discrimination.However,it couldn't measure the ambient RI.Therefore,a compact sensing system by combining HiBi-FLM with a multimode interference structure was proposed.Simultaneous measurement of refractive index and temperature was achieved with high resolution.On the basis of a large number of domestic and foreign literatures,this thesis has completed the following research work contents:(1)In order to determine the length of high-birefringence fiber in HiBi-FLM,basic principles and sensing properties of HiBi-FLM have been studied.The output spectra of HiBi fiber loop mirror were deduced by Jones matrix,and some simulations were carried out by Matlab.The results showed that FLM had good sensing properties when the length of high-birefringence fiber is 20 cm.(2)In order to determine the length of coreless fiber in the multimode interference structure,basic principles and sensing properties of multimode interference have been studied.Some simulations were carried out by Rsoft,and they showed that the multimode interference structure had good sensing properties when the length of coreless fiber is 3 cm.(3)In order to verify the results in theory and simulations,a temperature and refractive index sensing system based on HiBi fiber loop mirror and multimode interference has been established.The relationship between temperature,refractive index and resonance wavelength was studied.Experimental results showed that the temperature sensitivity was 1.795 nm/? and the RI sensitivity was 95.03 nm/RIU.The temperature and RI cross sensitivity problem was solved,and double parameters measurement was implemented.High resolution of 1.05 × 10-5 RIU had been achieved for RI sensing.Meanwhile,the temperature resolution was 0.01?.In this thesis,a novel design for simultaneous measurement of refractive index and temperature was proposed and experimentally demonstrated.The advantages of HiBi fiber loop mirror and multimode interference structure were utilized fully,which made the sensitivity of temperature and refractive index reach a higher level.As the sensor configuration featured the adavantages of easy to implement,simple structure and high sensitivity,it exhibited great potential applications in biological and chemical sensing.