Kefeng Li

Compact broadband amplified spontaneous emission in Tm3+-doped tungsten tellurite glass double-cladding single-mode fiber.

We reported the ~2 μm amplified spontaneous emission (ASE) performance of highly Tm3+-doped (3.76 × 1020 ions/cm3) tungsten tellurite single-mode fibers. The double-cladding fiber was pumped by a commercial 792 nm laser diode without any reflectors. Broadband ASE spectra with the bandwidth (FWHM) varying from ~45 nm to ~140 nm were achieved in a fiber length of 34 cm. The maximum output power was ~34 mW, with a slope efficiency of 4.8%. The ASE beam quality factor (M2) was 1.8. The dependence of output power, ASE mean wavelength, and bandwidth on the launched pump power and fiber length were discussed in detail.

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 laser properties of Tm 3+ -doped large core sol-gel silica fiber

Tm3+-doped 0.1Tm2O3-1Al2O3-98.9SiO2 (mol%) silica glass with good uniformity was prepared by sol-gel method combining with high temperature sintering. The core glass sized Φ3.2 × 50 mm with Δn of 5 × 10−4 was obtained after gelation, heat treatment, melting and polishing. Its spectroscopic properties were evaluated according to the detected absorption and fluorescence spectra. The maximum emission cross-section of Tm3+ ion in this glass is 6.2 × 10−21 cm2 and tested fluorescence lifetime is 836 μs at 1806 nm. Large core double cladding fiber with core NA of 0.102 was prepared by rod-in-tube and high temperature drawing. Its tested optical loss is 1.1 dB/m at 1333 nm. 1.11 W fiber laser output centered at 1969 nm with M2 factor of 1.99 was obtained from a 140 cm length double-cladding fiber with core diameter of 38 μm. The quasi-single mode laser with M2 factor of 1.33 was achieved in the fiber with core diameter of 19 μm.

0.5-GHz Repetition Rate Fundamentally Tm-Doped Mode-Locked Fiber Laser

We demonstrate a passively mode-locked Tm-doped silica fiber laser with 535-MHz fundamental repetition rate by employing a semiconductor saturable absorber mirror. With in-band pumping at 1590 nm, the stable mode-locked fiber laser produces up to 50 mW at an incident pump power of 558 mW. The laser operating at 1938 nm has a spectral bandwidth of 0.72 nm. After amplification, the laser pulse width is measured to be ~7.9 ps, and the time-bandwidth product is ~0.46.

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.

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.

High-power 2.04 μm laser in an ultra-compact Ho-doped lead germanate fiber.

A highly Ho-doped single-mode lead germanate glass fiber is developed for compact ∼2  μm lasers. Over 600 mW of laser output operating at 2.04 μm is demonstrated in a 2 cm-long active fiber. The slope efficiency reaches ∼34.9% with respect to the launched 1.94 μm laser pump power. To the best of our knowledge, this is the highest laser output power demonstrated within a few centimeters of a Ho-doped fiber. This result shows that the fiber is highly promising for high-power single-frequency laser applications.

~2 μm laser output in short length highly Tm3+-doped tungsten tellurite glass double cladding fiber

Highly Tm3+-doped tungsten tellurite glass double cladding fibers were prepared by using rod-in-tube method. A 306 mW laser output at ~2 μm was demonstrated from a 8.9 cm length of this fiber.