Study On Fabrication Of Tm³⁺-doped Silica Fiber And Tm³⁺-doped Fiber Laser

Compared with conventional bulk solid-state lasers,fiber lasers have become an international hotsopt and developed rapidly due to the advantages of high efficiency,easy heat management,good beam quality,compact configuration and good environmental stability.Operating in the eye-safe region,Tm-doped fiber laser(TDFL)allows various applications such as military,aerospace,biomedical,material processing and excellent pumping source for the mid-infrared supercontinuum source,optical parametric oscillator and Ho-doped fiber laser.However,compared with the western countries,the development of domestic high-power TDFL is relatively slower,and the TDF supply has long term dependence on import.Hence,the key parameters of TDF are needed to be explored in depth to realize the high-performance TDF which can replace the imported products,and achieve the high-power TDFL with stable operation further.Firstly,the fabrication of TDF employing modified chemical vapor deposition(MCVD)technique with solution doping method and preform drawing were introduced.The key parameters were analyzed to achieve TDF with high doping concentration and high absorption coefficient.Based on the techniques above,two double-clad TDFs with the core/cladding size of 10/125 and 25/400 were fabricated respectively.A series of tests showed that the laser performance of the two fibers have reached the international commercial level.Based on the homemade 25/400 LMA-TDF,we built an all-fiber 530 W high-power Tm-doped master-oscillator power-amplifier with narrow-linewidth.The oscillator yielded a maximum laser power of 91 W with a slope efficiency and 3 d B linewidth of 49% and 76 pm,respectively.In the amplifier stage,by optimizing the performance of splices and thermal management of the TDF,the output power was scaled to 530 W via bi-direction pumping method,corresponding to the slope efficiency of 50%.The central wavelength of output laser was 1980.89 nm.This result is the highest output power of domestic fiber laser operating at 2 ?m and validated the reliability of the homemade LMA-TDF.Based on the homemade highly doped 10/125 TDF,an all-fiberized mode-locked picosecond TDFL was built by employing SESAM and nonlinear amplification loop mirror.By controlling the polarization state in the cavity,the picosecond TDFL could operate in a stable soliton state and achieve self-start,corresponding to a maximum single pulse energy of 0.94 n J.The central wavelength of pulse was 1918.3 nm.To meet the needs of a variety of applications,the birefringence filter effect was introduced into the laser cavity by adding a high nonlinear fiber with optimized length.A tunable wavelength range of 1908~1952nm was achieaved.The tunable TDFL was amplified by employing 2 m 10/125 TDF as gain medium.The maximum slope efficiency of 33.7% was achieved at 1928 nm.The photodarkening(PD)effect is considered as major limiting factor of high-power fiber lasers to boost output power and operate stablely.The PD effect was studied and analyzed from characterization and suppression.An integrated platform for rapid PD and measurement was built,and the relationship between PD-induced excess loss and time was established as standard stretched exponential function.The bleaching effect of deuterium on the photodarkened TDF was verified for the first time.After 7 days of D2 loading at room temperature,about 88% of PD-induced excess in the visible region was eliminated.PD resistance of the D2 pretreated TDF has been investigated as well.The detailed thermal bleaching process of photodarkened TDF was demonstrated.The excess loss in the photodarkened TDF began to decrease when the temperature reached 250 ? and was completely eliminated at 550 °C.With the combination of theoretical and experimental analysis,the blue or ultraviolet light generated by upconversion process was considered to be one of the factors inducing color center.The mechanism of PD bleaching based on the theory of defect healing was studied and analyzed.