Characteristics Investigation And Fabrication Of Spliced Long Period Fiber Grating

Fiber gratings could directly modulate the wave modes on millimeter and even micrometer scale,and possess the advantages of light weight,good stability,high anti-interference,and so on.It has been widely used in the field of optical communications and sensors,and it will plays vital role in the new generation IT.With the gradual deepening of the research on long period fiber grating,some new structure of long period fiber grating has attracted attention widely.In this paper,a new spliced long-period fiber grating?LPFG?was fabricated based on the single-mode fiber?SMF?and multi-mode fiber?MMF?.A cleaving-splicing device is designed and fabricated which can be used to produce a spliced LPFG.To study its sensing properties,the spliced LPFG were applied to temperature,curvature,strain measurement by observing the evolution of the grating transmission spectrum.Then,a temperature-insensitive high curvature sensor were proposed and experimentally achieved.In addition,combining this LPFG and another LPFG can be used for simultaneous strain and temperature measurement.The manufacturing method provides a new approach of fabricating LPFG.The main contents and research results are as follow:1.A set of optical fiber cleaving-splicing device is designed and fabricated.Based on this device,a spliced long period fiber grating with a period of several hundred microns was made.This method does not need expensive instruments,just need the most common three-dimensional adjustment frame,fiber cleaver and optical fiber fusion splicer to achieve LPFG fabrication.The LPFG made by this method has the characteristics of high strength,small size and low production cost.2.After analyzing some kind of all fiber Mach-Zehnder interferometer and some new structure LPFG,it was first proposed the new spliced LPFG made by splicing single-mode fiber and multi-mode fiber alternately.The period of this spliced LPFG is 600?m,including400?m SMF and 200?m MMF.Due to the core diameter of SMF is much smaller than MMF,input light transmit from lead-in SMF to MMF to SMF,the high-order modes are excited periodically.Part of high-order modes will be coupled back into the core of SMF and others will be coupled into multiple forward-propagating cladding modes.The proposed LPFG has a high curvature sensitivity on all bend direction.It can be used as a good curvature sensor with the sensitivity of-22.4 nm/m^-1.3.Cascading spliced LPFG and CO₂-LPFG,the space between two types LPFG is 7mm.The transmission spectrum preserve their resonance peak respectively,which means this cascaded structure integrated all sensing characteristics of two LPFGs.Due to these two types of LPFG has different sensing characteristics on temperature and strain,simultaneous strain and temperature measurement can be achieved.Then,demodulation matrix has been figured up according to experimental data.