Single crystal fiber composed of rare earth doped YAG offers the potential for high power scaling of fiber lasers due to it lower intrinsic stimulated Brillouin cross-sections and higher thermal conductivity. The use of rare earth doped YAG fibers also mitigates issues associated with photodarkening, as well as issues associated with the silica multiphonon edge absorption and OH- quenching observed in Ho doped silica fiber lasers operating at eye safer wavelengths. To date, small diameter single crystal YAG fibers as small as 17 µm have been grown at Naval Research Laboratory to achieve a core architecture. Recent work has focused on development of cladding structures on the single crystal core material through sputtering, liquid phase epitaxy, and hydrothermal crystal growth to achieve a true core/clad all- crystalline wave guiding structure. Crystalline claddings have been grown with all three approaches with varying degree of quality and crystallinity. In this paper, we will report on our progress in fabricating crystal claddings on YAG single crystal core material.
Various rare earth doped single crystal YAG and sesquioxide fibers have been drawn using a state-of-the-art Laser Heated Pedestal Growth system. All crystalline core/clad fibers where thermal and optical properties are superior over glass based fibers have been successfully fabricated using various crystal growth and deposition methods. We report on the various fabrication methods, optical characterization of these clad fibers.
Single crystal fibers are currently being developed for high power single frequency lasers in 1-2 µm region. Crystal fibers offer several advantages over traditional glass fibers such as silica fiber due to their higher thermal conductivity and higher stimulated Brillouin scattering (SBS) thresholds, along with excellent environmental stability and higher doping concentrations. Yb3+ and Ho3+ doped single crystal YAG fibers with diameters down to 17 µm and lengths >1m long have been grown using our state-of-the-art Laser Heated Pedestal Growth system. Single and double cladded rare earth doped crystal fibers have been fabricated using glasses where optical and physical properties were precisely matched to the core single crystal fiber. We also show successful fabrication of all crystalline core/clad fibers where thermal and optical properties are superior over glass based fibers. Various fabrication methods, optical characterization and gain measurements on these clad fibers will be reported.
We report on the recent progress in the development of cladded single crystal fibers for high power single frequency
lasers. Various rare earth doped single crystal YAG fibers with diameters down to 17 μm with length > 1 m have been
successfully drawn using a state-of-the-art Laser Heated Pedestal Growth system. Single and double cladding on rare
earth doped YAG fibers have been developed using glasses where optical and physical properties were precisely
matched to doped YAG core single crystal fiber. The double clad Yb:YAG fiber structures have dimensions analogous
to large mode area (LMA) silica fiber. We also report successful fabrications of all crystalline core/clad fibers where
thermal and optical properties are superior over glass cladded YAG fibers. Various fabrication methods, optical
characterization and gain measurements on these cladded YAG fibers are reported.
Mid-infrared sources are a key enabling technology for various applications such as remote chemical sensing, defense communications and countermeasures, and bio-photonic diagnostics and therapeutics. Conventional mid-IR sources include optical parametric amplifiers, quantum cascade lasers, synchrotron and free electron lasers. An all-fiber approach to generate a high power, single mode beam with extremely wide (1μm-5μm) and simultaneous wavelength coverage has significant advantages in terms of reliability (no moving parts or alignment), room temperature operation, size, weight, and power efficiency. Here, we report single mode, high power extended wavelength coverage (1μm to 5μm) supercontinuum generation using a tellurite-based dispersion managed nonlinear fiber and an all-fiber based short pulse (20 ps), single mode pump source. We have developed this mid IR supercontinuum source based on highly purified solid-core tellurite glass fibers that are waveguide engineered for dispersion-zero matching with Tm-doped pulsed fiber laser pumps. The conversion efficiency from 1922nm pump to mid IR (2μm-5μm) supercontinuum is greater than 30%, and approaching 60% for the full spectrum. We have achieved > 1.2W covering from 1μm to 5μm with 2W of pump. In particular, the wavelength region above 4μm has been difficult to cover with supercontinuum sources based on ZBLAN or chalcogenide fibers. In contrast to that, our nonlinear tellurite fibers have a wider transparency window free of unwanted absorption, and are highly suited for extending the long wavelength emission above 4μm. We achieve spectral power density at 4.1μm already exceeding 0.2mW/nm and with potential for higher by scaling of pump power.
Mid Infrared (MIR) fiber optics has gained a great deal of interest over the past several decades. Applications range from passive transport to fiber lasers and nonlinear applications. These fibers have found use in a wide array of fields such as sensing, military countermeasures, scientific instrumentation, medical instrumentation, and in research laboratories. As with all fiber development there is a continual urge to seek better performance characteristics including transparency over a wide wavelength range, corrosion resistance, high power handling and low loss. We report on development of tellurite glass fibers displaying exceptionally high performance for various applications including wide band, low loss passive transport for mid IR, high efficiency, wide wavelength range and high power supercontinuum generation from visible to MIR wavelengths >4.5um, and active doping in fibers for use in laser cooling. High performance in each of these areas of interest has been brought about by development of a stable glass formulation and advanced processing techniques to remove impurities ions, entrapped hydroxyl, and scatter centers which allow fibers to be made with exceptionally low losses ~0.2dB/m.
We present our experimental and theoretical results of optical cooling in Tm-doped glass fibers as optical cooler pumped by single-mode, high efficiency and high power Tm-doped glass fiber lasers. The effects of impurities including OHabsorption and transition metals have been investigated systematically using different purified glasses for fiber fabrication. Our experimental results of spectroscopic measurements show temperature drops of more than 30 degrees from room temperature with pump powers of less than 3W. The results are in good agreement with theoretical simulation.