Optical cooling in an all fiber system using fiber laser pumps and cooling fibers doped with rare earth ions has been
investigated both theoretically and experimentally. A 2% Tm doped germanate glass was selected from glasses with
different Tm concentrations 0.5, 1, 2, 3, 4, 5, 6, 8 and 10% wt for fabrication of the cooling fiber. A high efficiency,
single mode Tm-doped fiber laser has been built to pump a Tm-doped fiber cooler. The cooling experiments done in a
vacuum chamber show indications that cooling has occurred in the fiber. A theoretical framework to understand the
nature of cooling in this laser cooling system has been developed which highlights the cooling power available as a
function of various material and fiber parameters including background loss and absorption saturation effects in the
cooling fiber. Cooling characteristics, with special emphasis on the fiber's saturation behavior, have been studied using
theoretical models of Tm<sup>3+</sup>-doped glass (4-level models) and Tm<sup>3+</sup> doped KLa(WO<sub>4</sub>)<sub>2</sub> crystals (20-level model).
A single frequency fiber laser operating near 2 micron with over 50 mW output power has been demonstrated by using a short piece of newly developed single mode holmium-doped germanate glass fiber. Laser from 2004 nm to 2083 nm was demonstrated from a short Ho-doped fiber laser cavity. A heavily thulium-doped germanate fiber was used as an in-band pump source for the holmium-doped fiber laser. The single frequency fiber laser can be thermally tuned.
Organic-inorganic hybrid sol-gel materials have attracted increasing attention in recent years as low-cost, rugged materials for integrated optical devices such as optical couplers, splitters, and electro-optic modulators. These materials can be easily processed by spin-coating, wet-etching photolithography, and low-temperature baking. Precise control of waveguide core-cladding refractive indices produces well-confined low-loss propagation and good matching of the absolute refractive index to that of fused silica results in low optical coupling loss to optical fiber. The increased thermal and mechanical stability of these materials, relative to optical polymers, results in numerous packaging options and improved reliability. However organic-inorganic hybrid sol-gel materials have not yet been often used as host of active dopants such as erbium (III) ions for 1550nm optical amplification. This limitation owes primarily to matrix and chelate dominated nonradiative relaxation processes, as high phonon energy OH and OH-like oscillators can bridge off the energy from the excited erbium (III) ions at very high rates. Different strategies have been proposed to protect erbium (III) ions from matrix and chelate quenching, including host and ligand fluorination, and inorganic microstructure shielding. Here we report on our work of encapsulating erbium (III) ions in transparent, refractive index matched, and highly re-dispersible lanthanum phosphate nanoparticles and the work of examining the optical properties of these nanoparticles as active dopants in organic-inorganic hybrid sol-gels adopting 2-methacryloxypropyl trimethoxysilane (MAPTMS) as a precursor. 980nm laser pumped photoluminescence at 1535nm was obtained from solid bulk samples of 300mg La.<sub>99</sub>Er.<sub>01</sub>PO<sub>4</sub> nanoparticles doped in 1mL hybrid sol-gel. Thick bulk samples of this composition exhibited exceptional clarity and little trace of nanoparticle scattering effects. The lifetime of the nanoparticle doped hybrid sol-gel composite was measured to be 220μs, indicating an intermediate relaxation rate between that of an erbium organic complex and annealed erbium doped glass. La.<sub>99</sub>Er.<sub>01</sub>PO<sub>4</sub> nanoparticle doped hybrid sol-gel films were also prepared and the refractive index was measured to be 1.4966 at 1550nm, which is very close to that of optical fiber and provides a suitable index difference from an undoped and metal oxide tuned sol-gel at 1.4870 to comprise an efficient single-mode waveguide system.
A self-calibrating fluorescence spectroscopy technique was applied to study cross-relaxation <sup>3</sup>H<sub>4</sub>, <sup>3</sup>H<sub>6</sub> → <sup>3</sup>F<sub>4</sub>, <sup>3</sup>F<sub>4</sub>, and energy migration <sup>3</sup>H<sub>4</sub>, <sup>3</sup>H<sub>6</sub> → <sup>3</sup>F<sub>4</sub>, <sup>3</sup>F<sub>4</sub>, of the Tm<sup>3+</sup> Ions doped in the tellurite glass. These glasses are investigated for their use in realization of 2 micron fiber lasers. Micro and macro-parameters of the energy transfer and migration were calculated by the means of the model of phonon-assistant multi-polar interaction and hoping mode. Steady rate equation analysis was used to fit the experimental fluorescence ratio of samples with different concentrations. We found that high-order (dipole-quadrupole) interaction was the dominant mechanism in the energy transfer of Thulium ions.
Wavelength of 2000 nm single mode microsphere laser from highly
thulium doped tellurite glass microsphere was demonstrated by means of
fiber taper coupling. Laser wavelength was red shift from the emission
peak of thulium ions at 1800 nm.
Optical microdisk array fabrication with sol-gel techniques was investigated. The characteristics of the microdisk array doped with Rhodamine B were studied with pulsed laser excitation. The whispering-gallery mode (WGM) emission spectra were observed. The WGM is very sensitive to the external circumstance under certain condition. The possible application of microdisk array as sensor also was investigated. We found the amplified spontaneous emission produced from microdisk array is very sensitive to the trace of material detected. The result showed that the microdisk as a kind of sensor has potential application in integrated optics.