Design,Optimized Growth And Applications Of Photoelectric Information Functional Single Crystal Fibers

As a key material to promote scientific and technological progress and social development,artificial crystals have received extensive attention from governments and scientific researchers from all over the world.Since the beginning of the 21st century,the rapid development of modem industry and military defense has put forward new requirements for artificial crystal materials and promoted the development of crystal materials.Therefore,the research of crystal materials has gradually entered a diversified and brilliant new stage.Single crystal fiber(SCF),as a kind of quasi-one-dimensional functional crystal material,inherits the excellent physical and chemical properties of bulk single crystal and possesses the structural advantages of large aspect ratio of traditional fiber materials.It has been widely used in many fields,such as high-power laser,high temperature sensing,radiation detection,information communication and so on.At present,United States,France and Japan are the leading countries in the research of SCF.Among them,companies represented by Fibercryst and Photran have realized the industrialization of SCF materials and SCF devices.Meanwhile,the US Army laboratory launched a laser weapon research project based on SCF in 2015,which highlights the importance of SCF in military defense and social livelihood.In domestic,the related research is relatively backward lacking of systematic research,advanced crystal growth equipment and mature crystal growth technology.In order not to be limited in the field of key materials,it is urgent to carry out relevant research.Laser heating pedestal growth(LHPG)is one of the most widely used tecnique for the growth of SCF with the advantages of saving raw materials,high heating temperature,fast heating speed,short experiment period and no crucible growth,which is mainly used to prepare high melting point SCF or flexible SCF.The US Naval Laboratory has fabricated a flexible YAG SCF with a diameter of 17 ?m through the LHPG method,which is also the smallest diameter single crystal fiber known,which is also the thinnest single crystal fiber so far.Guided by the application requirements of SCF in the field of optoelectronic information,this thesis focuses on the LHPG technique and solve the problems of diameter fluctuation,stress concentration and bubble wrapping during the growth of SCF.On this basis,the flexible YAG SCF was successfully fabricated,demonstrating a technological breakthrough.Besides,the characterization system of SCF is proposed and improved.Combined with the characterization methods of bulk crystal and glass fiber,the quality of YAG SCF is evaluated from crystal quality,diameter fluctuation,optical loss,optical uniformity and other dimensions.In terms of application research,related researches on SCF lasers and SCF temperature sensors have been carried out.Firstly,the causes and effects of the color centers in Yb:YAG single crystals are investigated and the watt-class CW laser output in the 1?m band was realized by using Yb:YAG without color center defectas as the laser gain medium.Secondly,the ultrasonic temperature measurement technology is combined with garnet and spinel SCF for the first time to develop a high temperature sensor with service temperature over 1800?.The influences of acoustic mode,crystal structure,ions doping and crystal orientation on the acoustic performance of SCF were mastered,and sensor performance is well improved.In addition,to meet the needs of ultra-high temperature temperature measurement above 2500?,the temperature sensor based on Y2O3-ZrO2 SCF with temperature-dependent electrical properties was designed,and the key properties such as service temperature range and temperature measurement sensitivity were characterized.The main research outline and conclusions of this thesis are as follows:?.Fabrication of high-qualty flexible SCF by LHPG methodWe have and systematically studied the main problems of skew growth,diameter fluctuations,stress concentration,bubble wrapping,and flexible crystal fabrication.The skew growth of SCF is solved by optimizing the optical path and improving the mechanical device.The diameter fluctuation of SCF is improved by optimizing the uniformity of pedestals and controlling the fluctuation of CO2 laser.Stress concentration inside the SCF has been well alleviated by reducing the diameter of the SCF and install resistance or optical after-heater.the bubble defects have been well avoided by increasing the density of the pedestals,adjusting the shape of the solid-liquid interface to flat or concave interface and setting the negative pressure growth environment.By replacing the spherical mirror with parabolic mirror,the focusing aberration is eliminated,which Lays the foundation for the growth of ultra-fine diameter flexible SCF.On this basis,for the first time,the flexible Yb:YAG laser SCF with a diameter of 150 ?m and a length-to-diameter ratio over2000:1 was growth through the LHPG method with a draw ratio of 36:1.?.Optimal growth,quality characterization and laser performance of Yb:YAG SCFOn the basis of the previous work,a high-quality Yb:YAG SCF without color center defects was growth by LHPG method in an inert atmosphere.It is found that the color center exists in Yb:YAG crystal are caused by oxygen vacancy and Yb2+ ions.The huge specific surface area of the SCF and the open melting zone of the LHPG technique enable oxygen ions to fully contact the melt and transmit,avoiding the occurrence of color center defects.The optical and thermal properties of Yb:YAG SCF are greatly improved by eliminating color center defects.The transmittance of Yb:YAG SCF in the near infrared band is more than 85%,and the thermal conductivity at room temperature is about 8 W·m-1·K-1.The quality of Yb:YAG SCF was evaluated from the aspects of crystallinity diameter fluctuation,doping uniformity,optical transmission loss and optical uniformity.The Laue diffraction spots of Yb:YAG SCF along the longitudinal direction are clear and bright and the diffraction pattern is consistent,indicating that the entire SCF has consistent orientation and good crystallinity.The optical loss of the SCF at 808 nm is about 0.01 dB/cm,which is equivalent to the experimental data of the US Army Laboratory.The results of the ZYGO laser plane interferometer show that the optical uniformity of the Yb:YAG SCF with the diameters of 1 mm and 2 mm can reach the order of 10-6,indicating excellent optical performance.On this basis,Yb:YAG SCF with the doping concentration of 2 at.%was used as gain medium,and the CW laser output with maximum power of 3.93 W and maximum slope efficiency of 28.2%was achieved.?.Garnet crystal fiber ultrasonic temperature sensorAn ultrasonic temperature sensor(UTS)with the service temperature over 1800?was developed by combining ultrasonic temperature measurement technology with YAG and LuAG SCF.The influences of ultrasonic mode,fiber diameter,crystal structure,ion doping and crystal orientation on the high-temperature acoustic properties of SCF and sensor performance were systematically explored.The experimental results show that the ultrasonic velocity decreases with the increase of temperature and the velocity of S-wave is far lower than that of P-wave at the same temperature.The S-wave velocity of YAG SCF is 4860.6 m/s at 1100?,which is about 3000 m/s lower than that of P-wave.Moreover,with the increase of Yb3+concentration,the ultrasonic velocity of YAG SCF further decreases,and the P-wave velocity of 2 at.%Yb:YAG SCF at 1100? is 4680.8 m/s.It is found that the acoustic anisotropy of garnet crystal fiber is relatively weak,and the anisotropy factors of YAG and LuAG are 1.05 and 1.07 respectively.Through the adjustment of acoustic wave mode,doped ions and orientation,the S-wave velocity of 10 at.%[111]-Yb:LuAG SCF-UTS in the range of 20-1100? reached 4198.26 m/s-3929.95 m/s,leading to the maximum unit sensitivity of 34.83 ns·?-1·m-1,and the maximum resolution of 2.87?.?.Anisotropic MgAl2O4 ultrasonic temperature sensorThe acoustic anisotropy of SCF depends on the elastic anisotropy.MgAl2O4 crystal exhibits significant elastic anisotropy with an anisotropy factor of 2.13,which is more than twice that of YAG/LuAG.MgAl2O4 shows different acoustic anisotropy behaviors in P-wave and S-wave mode,which are V[100]<V[110]<V[111]and V[110]<V[111]<V[100]respectively.The maximum and minimum ultrasonic velocities of MgAl2O4 SCF at 1200? are measured to be 9936.66 m/s and 3872.56 m/s,respectively,indicating a huge adjustment range.Combined with the previous work,[110]-(Mg0.9Zn0.1)(Al0.995Cr0.005)2O4 SCF-UTS was prepared by doping modification with the ultrasonic velocity of 4220.12-3738.04 m/s,the unit sensitivity of 40.38-67.50 ns·?-1·m-1 and the resolution of 1.24-0.74?.Both resolution and sensitivity are the best performance achieved by SCF-UTS so far.Furthermore,the performance of the sensor is positively correlated with ambient temperature,demonstrating huge application prospects in the field of ultra-high temperature sensing.?.Y2O3-ZrO2 SCF temperature sensor based on temperature-dependent conductivityThe melting point of Y2O3-ZrO2(YSZ)SCF exceeds 2700?,and it is insulated at room temperature.A large number of oxygen vacancies are introduced due to the non-equivalent substitution between Y3+and Zr4+ ions,making it conductive at high temperatures.Cubic-phase 8YSZ SCF were grown by the LHPG method and the electrical properties in the range of 20-1400? were explored in detail.Further research found that the ionic conductivity of YSZ single crystal fiber starts to be a certain function of ambient temperature when the temperature over 400?.The ionic conductivity and measurement sensitivity of 8YSZ SCF at 1400? are 0.531 S/cm and 0.129 S·m-1·?-1,which are more than 4 times that of 8YSZ ceramic fiber.Furthermore,the performance exhibits an upward trend with the increase of temperature,accompanied with the high melting temperature,resulting in a service temperature exceeds 2500?.