Design And Preparation Of Chalcogenide Long Period Fiber Gratings

Nowadays,silica long-period fiber gratings have been widely used in fiber-optic communication and sensing fields.However,the transmission range of silica materials is generally less than 2 μm,making the silica long-period fiber gratings not applicable in the mid-infrared(MIR)region.Because of its high importance in many applications bio-sensing,environmental monitoring,fiber optic devices suitable for the mid-infrared band deserves researching.Due to a series of wonderful characteristics,chalcogenide glasses becomes a new research hotspot.In this paper,the structural design and fabrication of long period fiber gratings(LPFG)based on chalcogenide glasses are studied systematically.In terms of the structural design of long-period sulfur fiber gratings,based on the coupled mode theory,high-sensitive long period fiber grating temperature sensor was designed based on the relationship between temperature and resonant wavelength.In addition,the gain-flattening effect of the chalcogenide long period fiber grating was analyzed.In the vacuum environment,chalcogenide glasses and chalcogenide fibers were prepared by the melt-quenching method and the extrusion method,respectively.The diffraction grating is prepared in chalcogenide glasses and thin films,and the refractive index modulation of chalcogenide glass induced by femtosecond laser is calculated according to the efficiency of diffraction grating.It provides an important guide for the accurate preparation of chalcogenide long-period fiber gratings.Finally,based on femtosecond laser writing technology,the preparation of chalcogenide long-period fiber gratings is studied.The results show that the chalcogenide long period fiber grating possesses higher temperature sensitivity at 1.55 μm,which is approximately 12 times than that of silica.In addition,due to the large refractive index(greater than 2.4)of the chalcogenide long period fiber grating,the external environmental refractive index has little effect on the resonant wavelength of the chalcogenide long period fiber grating.Therefore,the chalcogenide long period fiber grating has excellent sensing stability for the change of external refractive index.The study of refractive index changes of chalcogenide material caused by femtosecond laser-induced shows that with the increase of laser power,the diffraction efficiency of diffraction grating appears to increase first and then decrease.The refractive index of chalcogenide material caused by femtosecond lasers has reached a magnitude of 10-2.Based on the above work,the femtosecond laser direct-writing technology was used to carry out the preparation experiment of long-period fiber grating,then the transmission spectrum(1500~1600 nm)was obtained finally.