Presented here for the first time to the best of our knowledge is a detailed Brillouin spectroscopic study of novel, highly-BaO-doped silica glass optical fibers. The fibers were fabricated utilizing a molten-core method and exhibited baria (BaO) concentrations up to 18.4 mole %. Physical characteristics such as mass density, acoustic velocity, visco-elastic damping, and refractive index are determined for the baria component of the bariosilicate system. It is found that, of each of these parameters, only the acoustic velocity is less than that of pure silica. The effect of temperature and strain on the acoustic velocity also is determined by utilizing estimates of the strain- and thermo-optic coefficients. The dependencies are found to have signs opposite to those of silica, thus suggesting both Brillouin-frequency a-thermal and a-tensic binary compositions. Via the estimate of the strain-optic coefficient and data found in the literature, the Pockels' photoelastic constant p(12) is estimated, and both a calculation and measured estimate of the Brillouin gain versus baria content are presented. Such novel fibers incorporating the unique properties of baria could be of great utility for narrow linewidth fiber lasers, high power passive components (such as couplers and combiners), and Brillouin-based sensor systems.

Abstract:A nanoparticle (NP) doping technique was developed for fabricating erbium (Er)-and holmium (Ho)-doped silica-based optical fibers for high energy lasers. Slope efficiencies in excess of 74% were realized for Er NP doping in a single mode fiber based master oscillator power amplifier (MOPA) and 53% with multi-Watt-level output in a resonantly cladding-pumped power oscillator laser configuration based on a double-clad fiber. Cores comprising Ho doped LaF 3 and Lu 2 O 3 nanoparticles exhibited slope efficiencies as high as 85% at 2.09 µm in a laser configuration. To the best of the authors' knowledge, this is the first report of a holmium nanoparticle doped fiber laser as well as the highest efficiency and power output reported from an erbium nanoparticle doped fiber laser.

This paper, Part III in the Trilogy (Ballato, Cavillon, Dragic, 2018; Dragic, Cavillon, Ballato, et al., 2018a,b), provides a road map for the development of simple core/clad optical fibers whose enhanced performance-in particular, marked reductions in optical nonlinearities-is achieved materially and not through the more conventional present routes of geometrically complex fiber design. More specifically, the material properties that give rise to Brillouin, Raman and Rayleigh scattering, transverse mode instabilities (TMI), and n 2 -mediated nonlinear effects are compiled and results on a wide range of optical fibers are discussed with a focus on trends in performance with glass composition. Furthermore, optical power scaling estimations as well as binary and ternary property diagrams associated with Rayleigh scattering, the Brillouin gain coefficient (BGC) and the thermo-optic coefficient (dn/dT) are developed and employed to graphically represent general trends with composition along with compositional targets for a single intrinsically low nonlinearity, silica-based optical fiber that can achieve the power scaling goals of future high energy fiber laser applications. A foundational finding of this work is that the high-silica content optical fibers fabricated using conventional chemical vapor deposition methods will not suffice to meet the power scaling demands of future high-power and high-energy fiber lasers.

Utilizing measurements on a lanthano-aluminosilicate core optical fiber, the specific effects of lanthana (La₂O₃) on the Brillouin characteristics of silica-based oxide glass optical fibers are described. Lanthana is an interesting species to investigate since it possesses a wide transparency window covering the common fiber laser and telecom system wavelengths. As might be expected, it is found that the properties of lanthana are very similar to those of ytterbia (Yb₂O₃), namely, low acoustic velocity, wide Brillouin spectral width, and a negative photoelastic constant, with the latter two properties affording significant reductions to the Brillouin gain coefficient. However, lanthana possesses thermo-acoustic and strain-acoustic coefficients (acoustic velocity versus temperature or strain, TAC and SAC, respectively) with signs that are opposed to those of ytterbia. The lanthano-aluminosilicate (SAL) fiber utilized in this study is Brillouin-athermal (no dependence of the Brillouin frequency on temperature), but not atensic (is dependent upon the strain), which is believed to be, to the best of our knowledge, the first demonstration of such a glass fiber utilizing a compositional engineering approach.

Eu3+ doped LaF3 nanoparticles functionalized with a 3-4 formylphenyl benzoic acid ligand were synthesized. Excitation energy-dependent energy transfer from the ligand to Eu3+ yields color tunability from the red to greenish-blue as a function of excitation wavelengths. This synthetic approach provides large shifts in the resultant chromaticity with an excitation wavelength including the generation of white light.