Fabrication Of Liquid Core Fiber And Its Temperature Sensing Properties

With continuous development of kinds of temperature sensing probes,fiber temperature sensing probes(FTSPs)would become one of the most important research directions in measuring and monitoring temperature.Specially,FTSP performed outstanding merits in strong electromagnetic field.Temperature sensitivity,which directly affects the cost of sensing system and its recognition level to small temperature variation,is one of the most important parameter to evaluate FTSP.Therefore,it is very important to research a kind of FTSP that is easy to fabricate and to find ways to improve its temperature sensitivity.Hollow core fiber(HCF)performed well in various fiber sensors and received wide interest for its unique structure.In this paper,HCF was used for temperature sensing based on its principle of side-wall resonance.FTSP was fabricated with HCF and a way to improve its temperature sensitivity was found out.Compared with other FTSPs,owing to that the lossy dips in transmission spectrum and the temperature sensitivity have nothing to do with the spliced HCF,this kind of FTSP have the advantage of easy fabrication and easy to be mass produced.In the theoretical analysis for side wall resonant sensing structur e(SWRS),the light propagation model in the hollow core SWRS was studied for the first.The transmission spectrum formula was written out after making some simplification to the model.Then,the center wavelength formula of interference dips was written out on the basis of the transmission spectrum formula,and subsequently the temperature sensitivity.The sensitivity values were computed by two methods,simulating the transmission spectrum formula with MATLAB and calculating the temperature sensitivity formula.Next,after analyzing the temperature sensitivity formula of the hollow core SWRS,filling some liquid material with high thermo-optical coefficient into the hollow core is considered an effective way to improve the temperature sensitivity.The temperature sensitivity formula for the liquid core SWRS are then written out by amending the formula for the hollow core structure.Finally,to compute this sensitivity,three methods are employed,calculat ing the sensitivity formula,simulating spectrum formula of the liquid core stru cture and simulating the liquid core structure with the Rsoft.In the experiments,hollow core SWRSs with various HCF length were fabricated by fiber cutting and splicing method,and were used in high temperature sensing.And their temperature sensitivities were measured in the high temperature sensing experiments.Then,liquid core SWRSs with various HCF length were fabricated by filling and sealing a kind of liquid polymer in the air core of the hollow core SWRSs.Their temperature sensitivities were experimentally measured.Meanwhile,their repeatability,stability and response time in temperature sensing were also measured.At last,to improve their mechanical strength,silica capillaries were employed to package the liquid core SWRSs.And the response time of the packaged probe were also measured.The experimental transmission spectrums and temperature sensitivities of the hollow core SWRS and liquid core SWRS are both in accord with theoretical calculation and simulation.The hollow core SWRS can be used in high temperature sensing for its advantage of whole silica.But its temperature sensitivity is only about 28.97pm/?.With the method of filling liquid polymer in the air core,the sensitivity can be easily enhanced two orders of magnitude,up to 5.086nm/?.At the same time,this liquid core structure performed fine repeatability,wonderful linearity,good stability and short response time.