Fabrication And Optical Properties Of Rare Earth Ion Doped Glass Ceramic Fiber For Near/Mid-Infrared Fiber Laser

As a representative of the third generation of laser technology,fiber laser has the advantages of high laser output power,high optical conversion efficiency,tunable output wavelength,good stability,miniaturization and intensification,etc,and plays a vital role in the fields of modern communications,high-speed information network,industrial processing,biomedicine and others.Among the three elements that constitute the fiber laser,the gain medium is at the heart of the system.At present,most of the gain fibers studied are based on glass matrix.Due to its weak crystal field effect,the resulting laser performance in terms of output wavelength,power and conversion efficiency has reached a bottleneck.Therefore,it is urgent to develop new gain fiber materials.Glass ceramics,which combine the merits of good plasticity,tunable components and optical properties,low transmission loss of glass and strong crystal field,size controllability,outstanding luminescence performance of crystal,will show unique advantages as gain media in fiber lasers.In this dissertation,we firstly consulted literature to investigate the controllable fabrication method of glass ceramic fiber-melt-in-tube technique.Then,according to the working principle of this method,a series of rare earth ion doped glass ceramic fibers with high transparency were designed,optimized and fabricated.Finally,the laser performance of the fibers was studied and their potential applications in single-frequency fiber laser,ultra-short pulse fiber laser and mid-infrared fiber laser were explored.Based on the experimental exploration and theoretical analysis,a series of novel research achievements were obtained,which are summarized as follows:?1?Preparation of Yb³⁺-doped oxyfluoride glass ceramic fiber and investigation on the performance of?1.0?m ultra-short pulse laser.In this experiment,the design of core and cladding components,the fabrication process of glass ceramic fiber,and structural characterization and pulse laser performance were systematically explored,and the ultra-short pulse mode-locked laser was initiatively realized in the glass ceramics fiber.Based on the well-matched thermal and optical properties between the core and cladding materials,the fiber exhibits a good waveguide structure and no obvious element migration occurs.After proper heat treatment,Na YF₄ nanocrystals are uniformly precipitated in the fiber core,which provides a good coordination environment for Yb³⁺resulting in the significant enhancement of the optical performance.By establishing the optical test platform,1064 nm laser output with a threshold of 70 m W and slope efficiency of 30.0%is realized in the glass ceramic fiber.Furthermore,with the help of passive mode-locking technique,ultra-short pulse laser with pulse width of 8.1 ps and repetition frequency of 56.92 MHz is obtained.?2?Preparation of Er³⁺-doped oxyfluoride glass ceramic fiber and study on the performance of 1.55?m single-longitudinal mode laser.In this experiment,the advantages of nanocrystal-in-glass materials were employed to obtain enhanced laser output in the glass ceramic fiber and then the single-frequency laser output with high beam quality was further well-maintained structure was designed and fabricated by the melt-in-tube method.After heat treatment,KYF₄ nanocrystals are precipitated evenly in the fiber core and the evolution process of glass structure is demonstrated by the molecular dynamics simulations.Since active ions prefer to enter into the KYF₄ nanocrystal with low phonon energy after crystallization,the multi-phonon nonradiative relaxation is effectively suppressed and thus enhanced 1.55?m laser output is obtained in the glass ceramic fiber.In addition,by employing a linear short-cavity configuration,a single-frequency laser with a linewidth of7.4 k Hz and relative intensity noise of-148.8 d B Hz^-1 is further achieved.?3?Preparation of Tm³⁺-doped tellurate glass ceramic fiber and study on the properties of?2?m mid-infrared laser.This research focused on improving the?2?m laser performance and studied the laser behaviors of the glass ceramic fiber.Through a series of explorations,including component design,optimal Tm³⁺doping concentration,and the fabrication process of melt-in-tube method,the glass ceramic fiber containing Bi₂Te₄O₁₁ nanocrystal was prepared.The structural characterization shows that the fiber exhibits an integrated core-cladding configuration and good continuity.Benefited from the strong crystal field effect of nanocrystal,enhanced 1950 nm laser output is obtained in the glass ceramic fiber,and the slope efficiency increases from 8.8%to 14.1%.In addition,by employing the passive mode-locking technique,the Q-switched pulsed laser output is further realized in the glass ceramic fiber and the laser operation mechanism is theoretically analyzed.?4?Preparation of Er³⁺/Ho³⁺ codoped oxyfluoride glass ceramic fiber and investigation on the optical properties of?3?m broadband emission.In this experiment,based on the rare earth ion doping design and effective energy transfer,broadband?3?m mid-infrared emission was obtained in the oxyfluoride glass ceramic fiber with low phonon energy.Firstly,analyzed according to the changes of emission intensity and fluorescence lifetime as well as the energy level diagram.Secondly,the glass ceramic fiber containing Na YF₄ nanocrystal was controllably prepared by the melt-in-tube approach,where the core-cladding structure maintained well and no obvious element diffusion occurred.Finally,the mid-infrared emission performance of the glass ceramic fiber was experimentally studied.Owing to the heat treatment,intense mid-infrared emission was observed in the glass ceramic fibers,which was nearly undetectable in the as-prepared glass fiber with high phonon energy.Based on the effective energy transfer between Er³⁺and Ho³⁺,the 2.7?m emission was enhanced and the emission region showed a notable extension from 2.6-2.82 to 2.6-2.95?m after introducing Ho³⁺.Furthermore,theoretical simulation and calculation was conducted to demonstrate the potential application of the glass ceramic fiber in mid-infrared fiber laser.