Study On Optical/thermal Stability Of Chalcogenide Matrix Glasses For Fiber Grating

Fiber gratings is a highly efficient optical passive device which was established by forming a spatial periodic refractive index modulation on the core to change or control the propagation of light in the fiber.Since the first fiber grating has been successfully fabricated in the 1970 s,the research of silica-based fiber gratings have made great breakthroughs from theoretical design,simulation analysis to fiber gratings preparation in the past 30 years.These devices possess the advantages of small size,high sensitivity,and distributed measurement,which has been widely used in the field of fiber optic all-optical communication,fiber laser and fiber optic sensing.However,due to the limition of the infrared cut-off wavelength,the silica-based fiber can not be applied in the extremely important mid-infrared region.In recent years,with the development of laser technology and materials science,the fiber materials and devices in the mid-infrared have attracted great attention.Especially the chalcogenide-based matrix glasses have become an ideal recommendation for the developing of mid-infrared fiber devices due to its excellent infrared optical properties.Due to the photosensitive properties of the chalcogenide glass in the visible light region,chalcogenide fiber grating can be prepared by irradiation with continuous laser in the visible band.In addition,it is also possible to perform photolithography preparation using a femtosecond laser in the near-infrared band based on the multiphoton absorption effect of the femtosecond laser.At present,chalcogenide fiber gratings based on As2S3 and As2Se3 have been successfully prepared and used for fiber sensing and fiber lasers.Although As2S3 and As2Se3 glasses have excellent glasses forming regions and infrared transmission windows,the thermal stability of these glasses are very poor,the laser damage threshold of them are also low,which limits its application in high temperature and high power laser systems.Therefore,the development of chalcogenide-based glasses matrix materials with high optical and thermal stability are very important for improving the application range and device performance of chalcogenide fiber gratings in the mid-infrared range.In this thesis,the optical and thermal stability characteristics of chalcogenide glasses are systematically studied.The thermal stability and damage characteristics of the chalcogenide glasses with different component are systematically studied,the damage characteristics of the chalcogenide glasses under femtosecond laser irradiation with different laser parameter are also carefully analyzed.The main contents of the thesis include the following aspects:(1)The laser damage of the glasses with different component are firstly studied.The results shown that at both of the preparation wavelength(800 nm)and the working wavelength(4 ?m),the laser damage threshold increases with the increase of Ge content.The damage threshold of the preparation wavelength is lower than the damage threshold of the working wavelength.(2)The damage characteristics of chalcogenide glasses under laser irradiation with different laser parameter were further studied.It was shown that the depth of the focus has the greatest impact on laser damage;as the number of laser pulses increases,the laser damage threshold decreases rapidly.When the number reaches 100 or more,the value tends to be flat;and the increase of the laser repetition frequency makes the gradually decrease of the laser damage threshold.(3)The laser damage threshold of the fiber materials and the bulk materials at the preparation wavelength of 800 nm is also studied,which shown to be huge different.The damage threshold of fiber materials is higher than that of bulk materials.One of the very important reason is that the structure of fiber materials is more complicated than the bulk materials.The damage threshold of the fiber end surface is higher than the damage threshold of the fiber side surface.Therefore,for preparing a high-quality chalcogenide-based fiber gratings,the damage threshold of the bulk materials at the preparation wavelength can be used as the lowest reference value,and the damage threshold of the fiber side surface can be prepared as the main reference value for chalcogenide-based fiber gratings.(4)The theory of the structural design and characteristics of chalcogenide-based fiber gratings was finally carried out in this work.The chalcogenide fiber Bragg grating is first designed,which temperature sensing sensitivity has obvious advantages over that of silica fiber grating.The chalcogenide-based long-period fiber grating is then designed,whose temperature sensitivity is found to be higher than both of long period of silica fiber grating and chalcogenide fiber Bragg gratings.