Xiaokang Fan

Spectroscopic properties and quenching mechanism of 2 μm emission in Ho 3+ doped germanate glasses and fibers

The 2 μm emission spectra and lifetimes of Ho3+ ions in germanate glasses with different doping concentrations were investigated. The Judd-Ofelt parameters, radiative transition rates, and emission cross-section of Ho3+ were calculated based on the absorption and emission spectra. The energy transfer rate to hydroxyl groups and non-radiative rate of 5I7 level were calculated by fitting the variations of lifetimes vs. the doping concentrations. Besides, the unclad fibers with highly Ho3+ doped (6 × 1020 cm−3) were fabricated and pumped using a homemade 1.94 μm fiber laser, and the peak of emission spectra showed a redshift with the increasing fiber length.

∼2 μm emission properties and non-radiative processes of Tm3+ in germanate glass

In this paper, 80GeO2-8Ga2O3-10BaO-2Nb2O5-6PbO (in mol%) glass samples with different Tm2O3 concentrations (0, 0.5, 0.75, 1, 1.25, and 1.5 mol. %) were prepared by traditional melt-quenching method. According to the measurement of thermal properties of the host glass, the glass transition temperature is 596.7 °C and no crystallization peak is observed. Judd–Ofelt parameters Ωt (t = 2, 4, 6) and fluorescent lifetimes were obtained by Judd-Ofelt theory. The similar values of Judd–Ofelt parameters and the full-width at half-maximums of ∼1800 nm indicate the local environment of Tm3+ changes little with increment of Tm2O3 concentrations. Maximum stimulated emission cross-section of ∼1800 nm is 6.22 × 10−21 cm2 as calculated by Fuchtbauer–Ladenburg formula. Energy migration among Tm3+ ions was analyzed by the extended overlap integral method. The non-radiative transition rates between mainly energy levels of Tm3+ were calculated. Non-radiative transition rate of 3F4 energy level caused by OH was analyzed by ra...

All-Fiber Passively Q-Switched Laser Based on Tm 3+ -Doped Tellurite Fiber

We report all-fiber passively Q-switched Tm3±-doped tellurite fiber lasers. The composite tellurite fiber is specially designed to improve the mechanical strength. Both carbon nanotubes (CNTs) and semiconductor saturable absorber mirror (SESAM) are inserted separately into the laser cavities as SAs to demonstrate a fiber-integrated setup. In a short, 9-cm tellurite fiber, 1.86-μm-pulsed lasers without self-modelocking effect are demonstrated by in-band pumping at 1.59 μm. An average power of 84 mW is obtained in CNT-pulsed laser with 860-ns duration, whereas in SESAM-pulsed laser, the average power reaches 21 mW with 516-ns pulsewidth.

In-band pumping of Tm doped single mode tellurite composite fiber

Mechanical strength is one of the biggest limitations of practical application for tellurite fiber. In this study, we design and fabricate a single mode tellurite composite fiber to overcome the flaw. The fiber has a double cladding structure with tellurite core and inner cladding, the outer cladding, which is made of non-tellurite glass, possesses of appropriate softening temperature and coefficient of thermal expansion, well matched the novelty tellurite glass. The propagation loss of the fiber is less than 0.02 dB/cm @1310 nm. We also investigate the laser property of the fiber by using a homemade watt-class 1590 nm fiber laser. 2 micron fiber laser is demonstrated with a 2 cm length of the fiber.

A 2 μm continuous wave and passively Q-switched fiber laser in thulium-doped germanate glass fibers

In this study, we designed and fabricated a Tm 3+ -doped germanate glass fiber by using a rod-in-tube technique. The fiber has a core diameter of ~ 13.5 μm with a cladding of 125 μm. The Tm 3+ doping concentration reached ~13 500 ppm, and the propagation loss of the fiber was less than 0.03 dB cm − 1 at 1310 nm. Pumping with a 1590 nm fiber laser constructed in-house, a 44.7 mW continuous-wave fiber laser at 1940 nm was achieved in a 22 cm-long germanate fiber, with a slope efficiency of 26%. The passively Q-switched pulse output was first demonstrated by using a carbon nanotube saturable absorber in the germanate fiber. The germanate fiber laser generates approximately 1.5 μs pulses with a maximum pulse energy of 110 nJ, and the repetition rate varies from 15 to 84 kHz, depending on pump power.