Preparation,Characterization And Single Frequency Laser Technology Of Nd:YAG Crystal Derived Fiber

Crystal-derived fiber is a kind of widely used new fiber,which is made of crystal(such as YAG crystal)as the core material and SiO2 glass as the cladding material,using special fiber drawing tower and using melt in tube method.In the process of preparation of fiber,fiber core crystal materials in the molten state,SiO2 cladding in a state of softening,and wrapped in molten core crystal material,after graphite furnace heating system rapidly cooled to room temperature,directly across the middle of the crystal material crystallization temperature,reduce the abnormal crystallization of molten crystal materials,finally pulled crystal fiber.In principle,as long as we find the matching core material and cladding material,such as melting point(softening temperature),refractive index and expansion coefficient,we can prepare different kinds of special fibers with different characteristics and meet different needs.At present,special fiber prepared by fusion method has been widely used in laser,fiber high temperature sensing and semiconductor manufacturing.In recent years,rare earth ion doped YAG crystal-derived fibers prepared by core-fusion method have been widely used in single-frequency fiber lasers due to their advantages of low nonlinear effect,high thermal conductivity and high mechanical strength,and become a research hotspot.At present,the research on crystal-derived fiber mainly focuses on YAG crystal-derived fiber doped with rare earth ions such as Yb3+,Ho3+ and Tm3+ and the laser based on this fiber,while the research on Nd3+-doped YAG crystal-derived fiber is relatively few.On the basis of the previous research,Nd-doped Yttrium Aluminum Garnet(Nd:YAG)crystal derived fiber was prepared by means of core melting and secondary preparation.High doped Nd:YAG crystal was used as core material and high purity SiO2 glass as cladding material.High gain Nd:YAG crystal-derived special fiber was successfully prepared by special fiber drawing tower at?2000?,and its physical and optical properties were characterized and studied.Based on the high gain characteristics of Nd:YAG crystal-derived special fiber,a DBR structure single-frequency laser based on this fiber was designed,and the output of 1 ?m and 0.9 ?m single-frequency laser was achieved successfully.The main research contents are as follows:1.Briefly introduce the optical fiber drawing process,using 1.9 at.%,2.5 at.%Nd:YAG crystal as the core material,and selecting the appropriate concentration of Nd:YAG crystal as the core material The Nd:YAG crystal-derived fiber is prepared by the melt in tube method and the secondary drawing method.After adjusting the drawing tower parameters,the fiber core diameter is 12 ?m and the cladding diameter is 125 ?m.And without fiber coating,the bare fiber has good flexibility and robustness,and its core diameter and cladding diameter vary within the range of 10 ?m±1 ?m and 125 ?m±1 ?m,respectively.2.The drawn fiber with optimized parameters was used for characterization.The basic parameters of the optical fiber,such as the core and cladding diameter,the refractive index difference between the core and the cladding,and the numerical aperture.The unit length gain of the Nd:YAG crystal-derived fiber was measured through the optical path built by me.The unit length gain is 1.12 dB/cm@915 nm.The fluorescence emission spectrum and absorption spectrum of the fiber were measured.The transmission loss of the optical fiber is measured,and the transmission loss is 8 dB/m@1550 nm.In summary,the drawn Nd:YAG crystal derivative fiber is a very ideal gain medium for DBR short cavity lasers.3.After the experimental study of grating parameters and Nd:YAG Crystal derived fiber,the 9 mm long Nd:YAG Crystal derived fiber was used as gain medium.Through many tests,the HI 1060 fiber with the center wavelength of 1064.53 nm and the reflectivity of 99%and 77.8%was selected as the output grating,and the single frequency laser output of 1064.53 nm was finally obtained.4.Using 6 mm long Nd:YAG Crystal derived fiber as gain medium,the central wavelength of the grating is 915.3 nm,the reflectivity is 99%for HI 1060 grating and the reflectivity 95%for PM 980 grating.Nd:YAG crystal-derived fiber has fluorescence at 890 nm-910 nm,and blue shift to short wave direction compared with Nd doped SiO2 fiber.It is advantageous to obtain a shorter wavelength single frequency laser output.The low temperature characteristics of 915 nm fiber laser based on Nd:YAG Crystal derived fiber were studied by Tec refrigeration device.The laser operating conditions at 0?,10? and 20? were measured.The results show that the fluorescence emission spectrum of 915 nm fiber laser is enhanced in 880 nm-940 nm band at low temperature,which indicates that the emission spectrum of 915 nm fiber laser is enhanced in 880 nm-940 nm band The gain increases with the decrease of temperature in 915 nm band,which is beneficial to improve the output power of 915 nm Nd:YAG Crystal derived fiber laser.The innovation of this thesis is mainly as follows:1.By combining the MIT method with secondary preparation and improving the process,Nd:YAG crystal-derived fiber with high doping concentration was prepared,and the Nd:YAG crystal-derived fiber with high doping concentration was systematically characterized.2.Using 9 mm long Nd:YAG Crystal derived fiber as gain fiber and DBR structure,1064 nm single frequency laser output is realized.Based on the characteristics of low stimulated Brillouin scattering threshold,Nd:YAG Crystal derived fiber can be used as gain medium of 1064 nm single frequency high power laser.3.Using 6 mm long Nd:YAG Crystal derived fiber as gain fiber and DBR structure,915 nm single frequency laser output is realized.This is the first time that this fiber achieves single frequency laser output at 915 nm.The experimental results show that Nd:YAG Crystal derived fiber has the potential of single frequency laser in 890 nm-920 nm,and it is a potential gain medium for near infrared single frequency fiber laser.Using Tec refrigeration system,the output characteristics of DBR cavity laser based on Nd:YAG Crystal derived fiber at 880 nm-940 nm at low temperature are studied,which lays a foundation for the research of Nd:YAG Crystal derived fiber laser at low temperature.