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The hybrid approach of combining a Tm:YAG laser crystal with an amorphous fused silica tube is investigated to evaluate the suitability of the resulting crystal-derived fibers for efficient double-clad fiber lasers. The fabrication process and fiber properties of these Tm fibers are investigated, focusing on the dependence of the active fiber properties on the incorporated Tm3+ concentration. Crystal rods with different doping concentrations (TmxY1-x)3Al5O12 (x = 0.02, 0.05 and 0.08) were used as starting core material for fiber drawing. The investigated fibers are mechanically stable and result in a fairly homogenous and amorphous core glass with optical absorption and emission spectra that are similar to conventional Tm:Al doped silica fibers. Regarding laser properties with 790 nm cladding pumping, we could achieve a maximum slope efficiency of 47% with an output power of 4 W. The fiber laser results are compared to a conventionally fabricated double-clad Tm fiber prepared by Modified Chemical Vapor Deposition and solution doping. To the best of our knowledge, we demonstrate the highest laser output and the highest efficiency obtained from a Tm:YAG crystal-derived fiber.

The recently developed "flux assisted molten core method," used previously to fabricate GaAs core fiber with Sn as a solvent phase, is further extended here to Cu and Au fluxes. Unlike the GaAs:Sn system whose observed phases were the same in the precursor, as-drawn, and laser annealed fiber, the GaAs:Cu and GaAs:Au systems exhibited differing phases at each stage of the process. These systems undergo reactions during the molten core fiber fabrication and CO 2 laser post-processing. X-ray diffraction is employed to determine the phases resulting from As volatility during the pre-melt, fiber draw, and CO 2 laser post-processing. The phases, while unanticipated, are determined to be thermodynamically stable. In some of the systems, remnant Ga is suggested as being located in the flux compounds. This is a break with the conventional molten core method, where the fiber consists of the same phases as the starting material, and cases where reactions are driven in the molten core. The volatility of GaAs brings about unexpected reactions. • The flux assisted molten core method was employed to fiberize GaAs:Cu and GaAs:Au core fibers. • During the thermal processes, As volatilizes causing new phases to form with the Cu and Au fluxes. • The phases present in the as-drawn and annealed fibers, while unexpected, are thermodynamically stable phases. [ABSTRACT FROM AUTHOR]

The flux assisted molten core method, previously employed to fabricate glass-clad crystalline GaAs core fiber, is applied here to realize crystalline selenide and phosphide cores. These semiconductor families show great promise in photonics, optoelectronics, and thermoelectrics, although their volatility has previously prohibited successful fabrication utilizing the conventional molten core method. Through the introduction of a flux, the alloy melt temperature and associated vapor pressure can be sufficiently reduced to permit thermal drawing of the melt inside a glass cladding into fiber. Reported here are demonstrations of crystalline selenide and phosphide cores. Also reported is the CO 2 laser post processing of a ZnSe core fluxed with Cu 8 GeSe 6 , which resulted in lateral segregation of the ZnSe phase from the flux. X-ray diffraction and electron microscopy were deployed to determine the resulting ZnSe, InP and flux alloy phases and elemental distributions in the fiber core. X-ray diffraction of the InP: flux and most of the ZnSe: flux systems showed intermetallic flux phases that were not present on the phase diagrams reported in the literature. Formation enthalpy and phase diagrams of the intermetallic phases at room temperature were used to determine which observed phases were thermodynamically stable or meta-stable. The results indicate that the influences at play are primarily thermodynamic, but in some cases, kinetics plays a role during the fabrication of these fibers, forming metastable phases. Lastly, a review and discussion of the new demands on cladding glasses is presented for laser post-processing such fibers. This work demonstrates an approach to incorporating volatile and incongruently melting phases, that are not compatible with the standard molten core method, to realize novel in-fiber optoelectronic compositions. • The flux assisted molten core method was employed to fiberize crystalline selenide and phosphide semiconductor core fibers. • CO 2 laser post-processing on a ZnSe:Cu 8 GeSe 6 core fiber resulted in lateral segregation of ZnSe from the flux phase. • Thermodynamics mainly drives phase formation, but kinetics contributes to specific cases in crystalline core evaluation. • New requirements imposed on cladding glasses for fabrication and laser post-processing of fibers is discussed. [ABSTRACT FROM AUTHOR]

The molten core method (MCM) is a versatile technique to fabricate a wide variety of optical fiber core compositions ranging from novel glasses to crystalline semiconductors. One common feature of the MCM is an interaction between the molten core and softened glass cladding during the draw process, which often leads to compositional modification between the original preform and the drawn fiber. This causes the final fiber core diameter, core composition, and associated refractive index profile to vary over time and longitudinally along the fiber. Though not always detrimental to performance, these variations must, nonetheless, be anticipated and controlled as they directly impact fiber properties (e.g., numerical aperture, effective area). As an exemplar to better understand the underlying mechanisms, a silica-cladding, YAG-derived yttrium aluminosilicate glass optical fiber was fabricated and its properties (core diameter, silica concentration profile) were monitored as a function of draw time/length. It was found that diffusion-controlled dissolution of silica into the molten core agreed well with the observations. Following this, a set of first order kinetics equations and diffusion equation using Fick’s second law was employed as an initial effort to model the evolution of fiber core diameter and compositional profile with time. From these trends, further insights into other compositional systems and control schemes are provided.

The molten core method (MCM) is a versatile technique to fabricate a wide variety of optical fiber core compositions ranging from novel glasses to crystalline semiconductors. One common feature of the MCM is an interaction between the molten core and softened glass cladding during the draw process, which often leads to compositional modification between the original preform and the drawn fiber. This causes the final fiber core diameter, core composition, and associated refractive index profile to vary over time and longitudinally along the fiber. Though not always detrimental to performance, these variations must, nonetheless, be anticipated and controlled as they directly impact fiber properties (e.g., numerical aperture, effective area). As an exemplar to better understand the underlying mechanisms, a silica-cladding, YAG-derived yttrium aluminosilicate glass optical fiber was fabricated and its properties (core diameter, silica concentration profile) were monitored as a function of draw time/length. It was found that diffusion-controlled dissolution of silica into the molten core agreed well with the observations. Following this, a set of first order kinetics equations and diffusion equation using Fick's second law was employed as an initial effort to model the evolution of fiber core diameter and compositional profile with time. From these trends, further insights into other compositional systems and control schemes are provided. [ABSTRACT FROM AUTHOR]