Xufeng Jing

Mid-infrared fluorescence, energy transfer process and rate equation analysis in Er3+ doped germanate glass

Er3+ doped Y2O3 and Nb2O5 modified germanate glasses with different Er3+ concentrations were prepared. J-O intensity parameters were computed to estimate the structural changes due to the additions of Y2O3 and Nb2O5. The main mid-infrared spectroscopic features were investigated. To shed light on the observed mid-infrared radiative behavior, 975 nm and 1.53 μm emission spectra along with their decay lifetimes were also discussed. Moreover, the energy transfer processes of 4I11/2 and 4I13/2 level were quantitatively analyzed. In view of the experimental lifetimes, the simplified rate equation was utilized to calculate the energy transfer upconversion processes of upper and lower laser level of 2.7 μm emission. The theoretical calculations are in good agreement with the observed 2.7 μm fluorescence phenomena. Finally, the stimulated emission and gain cross sections were calculated and the results indicate that Er3+ doped germanate glasses have great potential for mid-infrared application.

Investigation of mid-infrared emission characteristics and energy transfer dynamics in Er 3+ doped oxyfluoride tellurite glass

Er3+ doped oxyfluoride tellurite glasses have been prepared. Three Judd-Ofelt parameters Ωt (t = 2, 4, 6) and radiative properties are calculated for prepared glasses. Emission characteristics are analyzed and it is found that prepared glasses possess larger calculated predicted spontaneous transition probability (39.97 s−1), emission cross section σem (10.18 × 10−21 cm2) and σem × Δλeff (945.32 × 10−28 cm3), corresponding to the 2.7 μm emission of Er3+: 4I11/2→ 4I13/2 transition. The results suggest that the prepared glasses might be appropriate optical material for mid-infrared laser application. Moreover, rate equation analysis which is rarely used in bulk glass has been carried out to explain the relationship between emission intensity and Er3+ concentration. The calculation results show that with the increment of Er3+ concentration, the energy transfer up-conversion rate of 4I13/2 state increases while the rate of 4I11/2 state reduces, resulting in the change of 2.7 μm emission.

Quantitative Analysis of Energy Transfer and Origin of Quenching in Er3+/Ho3+ Codoped Germanosilicate Glasses

The energy transfer mechanism between Ho(3+) and Er(3+) ions has been investigated in germanosilicate glass excited by 980 nm laser diode. A rate equation model was developed to demonstrate the energy transfer from Er(3+) to Ho(3+) ions, quantitatively. Energy transfer efficiency from the Er(3+):(4)I13/2 to the Ho(3+):(5)I7 level can reach as high as 75%. Such a high efficiency was attributed to the excellent matching of the host phonon energy with the energy gap between Er(3+):(4)I13/2 and Ho(3+):(5)I7 levels. In addition, the energy transfer microparameter (CDA) from Er(3+):(4)I13/2 to Ho(3+):(5)I7 level was estimated to (4.16 ± 0.03) × 10(-40) cm(6)·s(-1) via the host-assisted spectral overlap function, coinciding with the CDA (2,88 ± 0.04) × 10(-40) cm(6)·s(-1) from decay analysis of the Er(3+):(4)I13/2 level which also indicated hopping migration-assisted energy transfer. Furthermore, the concentration quenching of Ho(3+):(5)I7 → (5)I8 transition was the dipole-dipole interaction in the diffusion-limited regime, and the quenching concentration of Ho(3+) reached 4.13 × 10(20) cm(-3).

Broadband terahertz half-wave plate based on anisotropic polarization conversion metamaterials

We propose a half wave plate in the terahertz region to realize broadband linear polarization conversion in the reflection mode through anisotropic metamaterials. The structure of this design is composed of two pairs of patches in one unit cell that can rotate the polarization direction of a linearly polarized incident wave for an angle of 2β in a broadband frequency range. This work concentrates mainly on numerical simulations by using the standard finite difference time domain method. The efficiency of the half wave plate is higher than 50%, and PCR is higher than 85% in a broadband frequency range for cross polarization conversion. In the operating frequency band, three polarization conversion peaks can be found with the conversion efficiency nearly 100%. A more outstanding performance can be achieved by using low-loss substrate. The in-depth physical mechanism is revealed by further analysis. Besides, the expressions referring to theoretical decomposed electric field are deduced.

Enhancement of the accuracy of the simplified modal method for designing a subwavelength triangular grooves grating

The validity and accuracy of the simplified modal method for a highly efficient transmission subwavelength triangular grating are fully and quantitatively evaluated by a comparison of diffraction efficiencies predicted from the modal method to exact results calculated by a rigorous coupled wave analysis. The larger errors are revealed in smaller periods and in lower groove depths. More importantly, with the consideration of the reflection loss of the two propagating modes, the accuracy of the simplified modal method is significantly enhanced. The calculated diffraction efficiencies are in good agreement with the results of the vector method. This enhanced simplified modal method can be effectively used in the design of a shallower subwavelength grating. It is important to note that the consideration of the modal reflection loss can be applicable to any dielectric diffraction structure, e.g., the rectangular grating, in which the accuracy of the simplified modal method could be excellently improved to more exactly design a grating.

Validity of scalar diffraction theory and effective medium theory for analysis of a blazed grating microstructure at oblique incidence

The accuracy of scalar diffraction theory (SDT) and effective medium theory (EMT) for analyzing a blazed grating is quantitatively demonstrated by making a comparison of diffraction efficiencies calculated by the two simplified methods to exact results from the Fourier modal method (FMM). It is found that when the normalized period is more than fivefold wavelength of incident light at normal incidence and is more than about tenfold wavelength at larger incident angle, SDT can be used to easily analyze effectively the transmittance characteristics of a blazed grating with divergence less than 1%. Particularly, for zeroth-order diffraction when the groove depth is less than threefold wavelength, the transmittance calculated by SDT with refractive index of 1.5 and normalized period of 5.0 agrees well with that of FMM at normal incidence. But, for ±1 orders, the validity of SDT is degraded from that for zeroth order. Generally, the deviation of transmittances between the SDT and the FMM increases as the incident angle and refractive index augment. Furthermore, when higher diffraction orders other than zeroth order are not propagating, the EMT is valid to evaluate the transmittance of a blazed grating at normal incidence. Similarly, the error of transmittances between the EMT and the FMM increases with the increase of incident angle and refractive index. The effectiveness of the SDT and the EMT for analyzing a blazed grating in the range of the normalized period far more than and less than the wavelength of incident light, respectively, is dependent on the parameters including incident angle, refractive index, normalized period, and normalized groove depth.

Enhancement of 1.53 μm emission in erbium/cerium-doped germanosilicate glass pumped by common 808 nm laser diode.

Erbium-doped germanosilicate glasses with various cerium ions contents have been prepared. Optical absorption and 1.53 μm emission spectra were measured to characterize the spectroscopic performances of prepared samples. A detailed study of 1.53 μm spectroscopic properties was carried out when pumped by an 808 nm laser diode. Moreover, an energy level diagram and an energy transfer mechanism between Er3+ and Ce3+ were proposed to elucidate the enhanced 1.53 μm fluorescence. It is found that the prepared samples have optimal spectroscopic properties when the Ce3+ concentration is fixed to 0.5 mol. %. High spontaneous radiative transition probability (172.66  s(-1)), large effective emission bandwidth (74 nm), and emission cross section (9.49×10(-21)  cm(2) indicate that 808 nm pumped Er3+/Ce3+ codoped germanosilicate glass might be a suitable material for a broadband optical amplifier.

Ultrabroadband Unnaturally High Effective Refractive Index Metamaterials in the Terahertz Region

We demonstrate that an ultrabroadband, extremely high index of refraction can be realized from the thin window-type terahertz metamaterials composed of strongly multilayer coupled unit cells. By drastically increasing the effective permittivity by means of intense capacitive coupling and reducing the diamagnetic effect using a thin metamaterial structure, a peak refractive index of 70 at the resonant frequency, along with a low-frequency quasi-static value of over 18 were obtained for a single-layer thin ring terahertz metamaterial. A relative bandwidth of 0.5 THz at the index more than 20 can be observed for the single-layer thin window-type metamaterial with the refractive index peak achieving to 45. Based on the coupling effect of multilayer window-type metamatarials, the bandwidth of 1.25 THz with the index of more than 20 for the five-layer structure can be reached, and the refractive index peak reach to 50 while maintaining low losses. Importantly, the ultrabroadband performance with the bandwidth of 2.25 THz at the index larger than 20 was surprisingly indicated for multilayer coupling structure by a small incident angle. Simultaneously, the refractive index peak of more than 70 can be obtained.

Guided mode resonance in planar metamaterials consisting of two ring resonators with different sizes

We proposed and experimentally investigated a two-ring-resonator composed planar hybrid metamaterial (MM), in which the spectra of guided mode resonance (GMR) and Fano resonance or EIT-like response induced by coherent interaction between MM resonance and GMR can be easily controlled by the size of the two rings in the terahertz regime. Furthermore, a four-ring-resonator composed MM for polarization-insensitive GMRs was demonstrated, where GMRs of both TE and TM modes are physically attributed to the diffraction coupling by two ±45° tilting gratings. Such kind of device has great potential in ultra-sensitive label-free sensors, filters, or slow light based devices.

The influence of TeO2 on thermal stability and 1.53 μm spectroscopic properties in Er3+ doped oxyfluorite glasses

In this work, the thermal and spectroscopic properties of Er(3+)-doped oxyfluorite glass based on AMCSBYT (AlF3-MgF2-CaF2-SrF2-BaF2-YF3-TeO2) system for different TeO2 concentrations from 6 to 21 mol% is reported. After adding a suitable content of TeO2, the thermal ability of glass improves significantly whose ΔT and S can reach to 118 °C and 4.47, respectively. The stimulated emission cross-section reaches to 7.80×10(-21) cm(2) and the fluorescence lifetime is 12.18 ms. At the same time, the bandwidth characteristics reach to 46.41×10(-21) cm(2) nm and the gain performance is 63.73×10(-21) cm(2) ms. These results show that the optical performances of this oxyfluorite glass are very well. Hence, AMCSBYT glass with superior performances might be a useful material for applications in optical amplifier around 1.53 μm.