Jianli He

Intense 2.7 µm emission of Er 3+ -doped water-free fluorotellurite glasses

By physical and chemical dehydration techniques, a group of Er3+-doped water-free fluorotellurite glasses with a composition of 60TeO2-30ZnF2-10NaF(TZNF60,mol%)+x Er2O3(wt%,x=0~1.5) were fabricated. Under 978 nm excitation, the 4I(11/2)→4I(13/2) emission of Er3+ ions in TZNF60-glass was investigated: τ(f) is of 1.07~1.93 ms and emission bandwidth is about 163 nm at 2.71 µm, which benefits from the absence of OH groups and the decreased phonon energy with the addition of fluorides. In contrast, 1.25Er-TZNF60 glass is proposed to be a promising material for mid-infrared fiber lasers at around 2.7 µm.

1.23 μm emission of Er/Pr-doped water-free fluorotellurite glasses

To investigate the relatively unexplored 1.2 μm region, we identified a near-infrared emission at around 1.23 μm from Er3+/Pr3+-codoped water-free fluorotellurite glass with a composition of 60TeO2-30ZnF2-10NaF (TZNF60, mol. %). Under the condition of pumping with the 488 nm optical parametric oscillator (OPO) laser system, the directly measured lifetime (τ(f)) at 1.23 μm in Er/Pr-codoped fluorotellurite glasses is about 111.2 μs, much longer than that of Er-doped fluorotellurite glass (80.1 μs). The stimulated emission cross section (σ(em)) and quantum efficiency (η) for Er3+:4S3/2→4I11/2 transition are greatly enhanced when appropriate Pr3+ ions are incorporated. These advances arise partially from the absence of the hydroxyl (OH) group and low phonon energy with the addition of a large amount of fluorides into oxide-based host glasses. With high quantum efficiency (56.2%) and a large stimulated cross section (4.03×10(-21) cm2), Er3+/Pr3+-codoped TZNF60 glass is regarded as promising material for the development of optical amplification and laser operation at the relatively unexplored 1.2 μm region.

Intense red upconversion emission of Yb/Tm/Ho triply-doped tellurite glasses

By conventional melting and quenching methods, 3Yb2O3-0.2Tm2O3-xHo2O3 (wt%, x=0.2~1.2) was doped into an easily fiberized tellurite glass with composition of 78TeO2-10ZnO-12Na2O (mol%) to form YTH-TZN78 glasses. Under 976 nm excitation, the direct sensitizing effect of Yb ions (Yb→Ho) and indirect sensitizing and self-depopulating effects of Tm ions (Yb→Tm→Ho) were found to present intense red upconversion emission at 657 nm (Red, Ho:5F5→5I8) and were responsible for the absence of the usually observed 484 nm emission (Blue, Tm:1G4→3H36). Regardless of the dopant concentration of Ho ions, the intensity of the red emission at 657 nm (Red, Ho:5F5→5I8) is about three times stronger than that of the green one at 543 nm (Green, Ho:5S2→5I8). For this certain red emission at 657 nm, 0.4 wt% Ho2O3-doped YTH-TZN78 glass was found to present the highest emission intensity and is therefore determined as a promising active tellurite glass for red fiber laser development.

Nonlinear characterization of silver nanocrystals incorporated tellurite glasses for fiber development

To develop high nonlinear optical fibers for all-optical switching applications, 7.5 wt% AgNO<inf>3</inf> was incorporated into tellurite glasses with composition of 75TeO<inf>2</inf>-20ZnO-5Na<inf>2</inf>CO<inf>3</inf> (TZN75) under precisely-controlled experimental conditions to form 7.5Ag-TZN75 glass. Surface Plasmon resonance absorption peak of Ag nanocrystals embedded in 7.5Ag-TZN75 glass was found to center at 552 nm. By degenerated four-wave mixing method, the non-resonant nonlinear refractive index, n<inf>2</inf>, of 7.5Ag-TZN75 glass was measured to be 7.54×10⁻¹⁹ m²·W⁻¹ at 1500 nm, about 3 times of the reference TZN75 glass without any dopant and 27 times of the silicate glasses and fibers, and the response time is about 1 picosecond.

High Nonlinear Fluorotellurite Glass Fiber

We report on the fabrication of water-free fluorotellurite glass fiber with high nonlinearity. By the continuous-wave self-phase modulation method, the nonlinear refractive index n2 is estimated to be 1.4×10-18 m2/W at 1550 nm.

Mid-Infrared Fluorescence of Ho-doped Water-free Fluorotellurite Glasses

Ho3+-doped water-free fluorotellurite glasses and fiber canes were reported. Comparable long fluorescence lifetimes of 0.81 ms at 2.85 µm and 10.01 ms at 2.04 µm were obtained.

Design and Simulation of Large-Mode-Area Solid-Core Bragg Fiber

Solid-core Bragg fiber was proposed as a competitive solution for high power laser delivery. The optimized fiber is with effective area of 400 μm2 and low loss of 3 dB/km at 1.08 μm.

Multiring large-mode-area delivery fiber for high power

The study presents a novel design of multiring delivery fiber with large mode area for high power. Using a FiberCAD method, we investigated a fiber whose core is surrounded by alternative low- and high-index rings. Based on our calculation, the effective area is 400 μm2 at 1.08 μm, larger than the ~280 μm2 of conventional step-index fiber (20/400). The macrobending loss at 1.08 μm is estimated to be 1×10(-3) dB/m, approximately one-third that of conventional step-index fiber (20/400). The single-mode operation can be achieved by the macrobending loss contrast between the fundamental mode (<1 dB/m) and high-order mode (>100 dB/m). The results indicate that multiring delivery fiber fabricated by modified chemical vapor deposition process is a promising candidate for high-power transmission.

Silver nanocrystals incorporated tellurite glass for highly nonlinear fiber development

7.5wt% silver nanocrystals were successfully incorporated into an easily-fiberized tellurite glass with composition of 75TeO2-20ZnO-5Na2O (mol%). Surface Plasmon resonance absorption peak was found to be centered at around 552nm as the indirect evidence of silver nanocrystals with an average radius of 2.18nm.

Diode pumped CW mode-locked Yb:LuAG laser

Diode-pumped stable cw mode-locked laser in Yb:LuAG crystal was demonstrated. The pulse duration of 7.63ps was achieved without any negative dispersion elements. With pump of 8W, output power was 610mW with repetition rate of 86MHz.