Chunlei Yu

Magnetodielectric effects of Y3Fe5−xTixO12+x/2 ceramics

Dielectric, magnetic, and magnetodielectric properties of Y3Fe5−xTixO12+x/2 (x = 0, 0.1, 0.2) ceramics were investigated. Ti substitution induces a low temperature dielectric relaxation which comes from the charge carrier hopping between Ti3+ and Ti4+. The Maxwell-Wagner effect related dielectric relaxation becomes weak as the content of Ti increases. The extrinsic effect and intrinsic effect play a dominant role on the magnetodielectric effects for x = 0 at f < 500 kHz and f ≥ 500 kHz, respectively. The contribution of the extrinsic effects to magnetodielectric (MD) effect decreases and the contribution of the intrinsic effects to MD effect increases with increasing Ti amount.

Tunable white light emission from γ-irradiated Ag/Eu co-doped phosphate glass phosphor

We report a new tunable white light emission from γ-irradiated Ag/Eu co-doped phosphate glass phosphor. The appearance of Eu2+ and silver aggregates after γ-irradiation was confirmed via Electron paramagnetic resonance (EPR), absorption, and emission spectra. The effects of Ag/Eu doping concentration and excitation wavelengths on white light emission were discussed. A pure white light emission with the chromaticity coordinates (X = 0.331, Y = 0.329) was generated using the optimal sample under excitation at 360 nm.

Neodymium-doped phosphate fiber lasers with an all-solid microstructured inner cladding

We report on high-power fiber lasers based on index-guiding, all-solid neodymium-doped (Nd-doped) phosphate photonic crystal fiber (PCF) with a hexagonal-shaped inner cladding. The optimum fiber laser with a 36 cm length active fiber, generated up to 7.92 W output power at 1053 nm, which benefited from a high absorption coefficient for pump power due to its noncircular inner cladding. The guiding properties of the all-solid PCF were also investigated. A stable mode with a donut-shaped profile and a power-dependent laser beam quality have been observed experimentally and analyzed.

Phosphate single mode large mode area all-solid photonic crystal fiber with multi-watt output power

An index-depressed active core, single-mode phosphate all-solid large-mode-area photonic crystal fiber (PCF) is theoretically investigated using full-vectorial finite difference approach and experimentally realized. The PCF has a maximum output power of 5.4 W and 31% slope efficiency. Single-mode operation is realized through PCFs with core diameters of 30, 35, and 40 μm, respectively. The beam quality is not degraded even at maximum output power. Our simulations and experiments reveal that the laser performance is significantly affected by the center-to-center distance between the two nearest rods Λ, the rod diameter d, and their ratio d/Λ, implying that much attention should be given in employing optimal parameters to achieve excellent laser performance.

Watt-level Yb-doped silica glass fiber laser with a core made by sol-gel method

A Yb-doped silica glass fiber laser with a core made by sol-gel method is reported. The maximum power of 1.14 W is obtained with a pump power of 5.46 W at a wavelength of 976 nm. The slope efficiency is 34%. The refractive index fluctuation across the core is below 5×10-4 at a doping level of Yb 0.15 mol%, A2O3 4.0 mol%, and P2O5 2.0 mol%. High background attenuation of 6 dB/m at 1 053 nm limites the slope efficiency and maximum output power.

Efficient Generation of Watt-Level Output From Short-Length Nd-Doped Phosphate Fiber Lasers

We report experimental results on high-power heavily Nd-doped phosphate continuous-wave (CW) fiber lasers of very short length. The optimum fiber laser with a length of 26 cm exhibited a maximum output power of as much as 2.87 W and a slope efficiency of 44.7% with respect to absorbed pump power at 795 nm. Up to 1-W laser was also obtained from a 6-cm-short active fiber. The fiber lasers were demonstrated at 1053 nm with a linewidth of 1.6 nm, and showed no evidence of roll-over even at highest output power. The output powers were stable and limited only by available pump power.

50 μm core diameter Yb³⁺Al³⁺/F⁻ codoped silica fiber with M²<1.1 beam quality.

This paper reports, for the first time to our best knowledge, a nearly diffraction-limited output in a Yb(3+)/Al(3+)/F(-) codoped double cladding silica fiber with a 50 μm core diameter and 0.02 core NA. The core glass with a diameter >6  mm was fabricated through solgel process combined with high temperature sintering. Laser performances of this fiber at different bend diameters were studied. The mean M2<1.1 in this 50 μm core diameter fiber was achieved at a bend diameter of 0.35 m. The core glass with the refractive index nearly equal to pure silica glass is suitable for the fiber design, such as large-mode-area photonic crystal fiber.

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.

Phosphate ytterbium-doped single-mode all-solid photonic crystal fiber with output power of 13.8 W

Single-mode ytterbium-doped phosphate all-solid photonic crystal fiber (AS-PCF) with 13.8 W output power and 32% slope efficiency was reported. By altering the diameter of the rods around the doped core and thus breaking the symmetry of the fiber, a polarization-maintaining AS-PCF with degree of polarization of >85% was also achieved, for the first time to knowledge, in a phosphate PCF.

Yb/Er co-doped phosphate all-solid single-mode photonic crystal fiber

An all-solid Yb3+/Er3+ co-doped single-mode phosphate photonic crystal fiber (PCF) with Watt-level output power and 20 μm core diameter is demonstrated for the first time. A PCF whose refractivity of the active core is lower than that of the background glass is suggested and theoretically confirmed to be in single-mode operation at 40 μm core diameter.