High Rare-earth Solubility Research Articles

(Invited) Rare-Earth-Doped Tellurium Oxide Light Emitting Nanophotonic Devices

Tellurium oxide is a promising material for passive, nonlinear and rare-earth-doped active photonic devices because of its high transparency, high refractive index, high nonlinearity and unique structure allowing for high rare-earth solubility. In this talk I present on our recent progress on tellurite glass on-chip light emitting nanophotonic devices. Low-loss passive devices including high-Q-factor microdisks and microring resonators will be discussed. In addition, rare-earth-doped active devices, including erbium-doped and thulium-doped waveguide amplifiers and microlasers will be presented. Using similar structures, we demonstrate nonlinear light emission via four-wave-mixing, supercontinuum generation and third harmonic generation. These tellurium oxide integrated nanophotonic devices are highly promising for compact and low-cost passive, active and nonlinear photonic integrated circuits for applications in communications, computing, and sensing.

Quantitative prediction of the glass‐forming region and luminescence properties in Tm3+‐doped germanate laser glasses

AbstractGermanate laser glasses have received much attention as a promising host materials for mid‐infrared fiber lasers in recent years because of the outstanding infrared transparency, low phonon energy, and high rare earth solubility of such glasses. However, the development of high‐performance germanate laser glasses is usually based on intuition and a trial‐and‐error method, which can involve long experimental periods and high costs, and thus, this approach is highly inefficient. Recently, with proposals for materials genome engineering, the concept of the “glass genome” has grown of interest to us. Herein, the structures of Tm3+‐doped germanate laser glasses (BaO–GeO2 and BaO–La2O3–GeO2) were investigated by Fourier transform infrared spectra (FTIR) and Raman spectra analyses, which revealed that the resulting glass contains similar structural groups to the neighboring congruently melted glassy compounds (NCMGCs) in the composition diagram. What is more, the structure and properties of the resulting laser glasses largely depend on NCMGCs. Then, the glass‐forming region, physical properties, and luminescence properties were calculated via the use of NCMGCs in Tm3+‐doped BaO–GeO2 binary and BaO–La2O3–GeO2 ternary laser glass systems. The calculated results were in good agreement with the experimental results, thus demonstrating that our approach is practical for predicting the glass‐forming region, physical properties, and luminescence properties in Tm3+‐doped BaO–GeO2 binary and BaO–La2O3–GeO2 ternary laser glass systems. This work may provide an effective method to develop Tm3+‐doped germanate laser glasses rapidly and at low cost.

Electroluminescence from silicon-based light-emitting device with erbium-doped TiO<sub>2</sub> films: Enhancement effect of ytterbium codoping

In the past years, light-emitting devices (LEDs) based on erbium (Er)-doped insulators or wide-bandgap semiconductors have received intensive attention because the intra-4f transition (<sup>4</sup>I<sub>13/2</sub>→<sup>4</sup>I<sub>15/2</sub>) of Er<sup>3+</sup> ions at ～ 1540 nm has potential applications in the optical interconnection for silicon-based circuits. The LEDs with rare-earth (RE)-doped SiO<i><sub>x</sub></i> (<i>x</i> ≤ 2) or SiN<i><sub>x</sub></i> (<i>x</i> ≤ 4/3) films have been well investigated as the silicon-compatible emitters. However, they suffer difficulty in injecting current and easing fatigue. In this context, the LEDs with RE-doped oxide semiconductors have been extensively investigated out of research interest in recent years. Among the oxide semiconductors, TiO<sub>2</sub> is a desirable host for RE-doping because it is transparent for visible and infrared light, and cost-effective, and has considerably high RE solubility. In our previous work (Zhu C, Lü C Y, Gao Z F, Wang C X, Li D S, Ma X Y, Yang D R 2015 <i>Appl. Phys. Lett.</i> <b>107</b> 131103), we have realized erbium (Er)-related visible and near-infrared (～ 1540 nm) electroluminescence (EL) from the LED with a structure of ITO/TiO<sub>2</sub>:Er/SiO<sub>2</sub>/n<sup>+</sup>-Si, in which TiO<sub>2</sub>:Er refers to the Er-doped TiO<sub>2</sub> film as the light-emitting layer. In this work, we co-dope ytterbium (Yb) into the TiO<sub>2</sub>:Er film in the aforementioned LED to significantly enhance the Er-related visible and near-infrared EL. It is revealed that a certain amount of Yb co-doping enables the TiO<sub>2</sub>:Er film to transform its crystal phase from anatase to rutile. Such a phase transformation reduces the symmetry of crystal field surrounding the Er<sup>3+</sup> ions incorporated into the TiO<sub>2</sub> host. Moreover, the substitution of over-sized Yb<sup>3+</sup> ions for Ti<sup>4+</sup> ions in the TiO<sub>2</sub> host leads to the distortion of the crystal field around the Er<sup>3+</sup> ions. The aforementioned symmetry-reduction and distortion of the crystal field increase the probabilities of the intra-4f transitions of Er<sup>3+</sup> ions. Due to the aforementioned reason, the Yb co-doping into the TiO<sub>2</sub>:Er film remarkably enhances the EL from the corresponding LED. It is believed that the strategy of Yb-codoping can be adopted to enhance the EL from the LEDs with other RE-doped TiO<sub>2</sub> films.

Silver metaphosphate glass wires inside silica fibers--a new approach for hybrid optical fibers.

Phosphate glasses represent promising candidates for next-generation photonic devices due to their unique characteristics, such as vastly tunable optical properties, and high rare earth solubility. Here we show that silver metaphosphate wires with bulk optical properties and diameters as small as 2 µm can be integrated into silica fibers using pressure-assisted melt filling. By analyzing two types of hybrid metaphosphate-silica fibers, we show that the filled metaphosphate glass has only negligible higher attenuation and a refractive index that is identical to the bulk material. The presented results pave the way towards new fiber-type optical devices relying on metaphosphate glasses, which are promising materials for applications in nonlinear optics, sensing and spectral filtering.

Spectroscopic properties of 2.7 μm emission in Er3+ doped telluride glasses and fibers

Emissions at 2.7μm from telluride glasses with various Er2O3 doping concentrations are investigated. The prepared glasses have excellent thermostability and high rare-earth solubility. Judd–Ofelt parameters are calculated based on the absorption spectra. A large emission cross section (1.12×10−20cm2) and a high spontaneous radiative coefficient (57.8s−1) are obtained at 2.7μm. The fluorescence properties of glasses with different concentrations are analyzed and presented. An Er3+-doped fiber is fabricated via a rod-in-tube technique, and the loss at 1310nm is ∼2.1dB/m measured by using the cut-back method. Strong upconversion emission caused by intense pump absorption is observed from the Er3+doped fiber under excitation by a 980nm laser diode (LD).Telluride glasses with high Er3+ doping concentration and good thermal property are prepared. Energy transfer processes for 1.5μm, and 2.7μm, as well as visible emission are fully discussed. Enhanced 2.7μm emission is achieved from the bulk glass. An Er3+ doped fiber is successfully drawn, and strong upconversion emission is observed in the fiber.

Coupling characteristics of a soft glass nematic liquid crystal photonic crystal fibre coupler

This study presents the coupling characteristics of a novel soft glass photonic crystal fibre (PCF) coupler infiltrated with a nematic liquid crystal (NLC–PCF). The soft glass provides optical properties that cannot be obtained by silica such as high refractive index, high rare earth solubility and mid-infrared transmission. In addition, the nematic liquid crystal (NLC) offers high tunability with the temperature and external electric field, and increases the birefringence between the two fundamental polarised modes in the proposed coupler. Therefore the NLC–PCF coupler has stronger polarisation dependence than the low birefringence conventional silica PCF coupler. The effects of the coupler geometrical parameters, rotation angle of the director of the NLC and temperature on the coupler performance are investigated. The analysis is carried out using the full vectorial finite difference method and the beam propagation study is performed by the full vectorial finite difference beam propagation method. The numerical results reveal that the polarisation dependence of NLC–PCF coupler is approximately 2.5 times that of the conventional silica PCF coupler with shorter coupling length. In addition, the NLC–PCF coupler has strong potential to offer practical design for short polarisation splitter as well as multiplexer–demultiplexer.

Relaxation process of the 4I13/2 level of Er3+ in a borosilicate glass

Abstract Relaxation of 1.54 μm emission of the erbium doped borosilicate glasses with high rare earth solubility was investigated. When the erbium content is less than 0.2 wt%, multi-phonon relaxation is the predominant process of non-radiative relaxation. It is difficult to increase the quantum efficiency higher than 70% for erbium ions in this glass due to multi-phonon relaxation. Because of the good glass-formation ability and high rare earth solubility, this glass will be suitable as a host for rare earth ions with a large energy gap, such as Yb3+, Eu3+ or Tb3+.

Emission properties of the [formula omitted] transition in Er 3+- and Er 3+/Tm 3+-doped Ge–Ga–As–S glasses

Ge–Ga–As–S glasses were investigated to develop efficient host materials for the Er 3+:2.7 μm fiber lasers. Ge 30Ga 1As 9S 60 and Ge 30Ga 2As 6S 62 (all in at.%) glasses show good thermal stability and high rare-earth solubility up to 0.3 mol%. Mid-infrared emission with a peak wavelength of 2.76 μm and bandwidth of ∼120 nm was observed in Er 3+- and Er 3+/Tm 3+-doped Ge 30Ga 2As 6S 62 glasses. Codoping of Tm 3+ significantly reduced the lifetime of the Er 3+: 4 I 13/2 level due to the energy transfer of Er 3+: 4 I 13/2→ Tm 3+: 3 F 4 . Thus, the population inversion between the 4 I 11/2 and 4 I 13/2 levels in Er 3+ became possible. In Er 3+-doped glasses, the rate of cross-relaxation for the 4 I 11/2 level was approximately 11 times faster than that for the 4 I 13/2 level.