Wideband subwavelength gratings for coupling between silicon-on-insulator waveguides and optical fibers

We propose and experimentally demonstrate a novel subwavelength grating coupler on silicon-on-insulator, for coupling to optical fibers with a wide optical bandwidth. Theoretical analysis and design optimization of the coupler are described. About 73?nm 1?dB bandwidth was experimentally demonstrated with -5.6 dB coupling efficiency. Better than -3.4 dB efficiency with 86?nm 1?dB bandwidth is predicted for these structures with optimized buried oxide thickness.     

Characterization of Pinched Ricci Curvature by Functional Inequalities

In this article, functional inequalities for diffusion semigroups on Riemannian manifolds (possibly with boundary) are established, which are equivalent to pinched Ricci curvature, along with gradient estimates, \(L^p\)-inequalities and log-Sobolev inequalities. These results are further extended to differential manifolds carrying geometric flows. As application, it is shown that they can be used in particular to characterize general geometric flow and Ricci flow by functional inequalities.     

Hydrostatic pressure sensor based on a gold-coated thin-core fiber modal interferometer and ripple shift measurement

We propose a hydrostatic pressure sensor based on a gold-coated thin-core fiber modal interferometer (TCFMI). A thin-core fiber is spliced to a single mode fiber forming a single-end fiber modal interferometer (FMI) due to the core mismatch and the fiber end reflection. Relative reflection spectra of TCFMIs based on thin-core fibers with different lengths are investigated. The TCFMI is gold-coated to enhance the optical reflectivity, which also results in the ripple of the relative reflection spectra of TCFMI. A high hydrostatic pressure sensor test system is proposed and the performance of the pressure sensor has been experimentally investigated. A pure-ripple-shift measurement method is used to achieve the demodulation of the sensor. The proposed pressure sensor has a sensing range up to 40 MPa and a sensitivity of 44.8 pm/MPa.     

Crystal growth,spectroscopic characterization and laser performance of Nd:Lu<Subscript>0.33</Subscript>Y<Subscript>0.36</Subscript>Gd<Subscript>0.3</Subscript>VO<Subscript>4</Subscript> crystal

A new three-matrix mixed vanadate crystal Nd:Lu_0.33Y_0.36Gd_0.3VO₄ (Nd:LuYGdVO₄) crystal was grown by the Czochralski method. Room temperature absorption and fluorescence spectra of the Nd:LuYGdVO₄ crystals were measured and the spectroscopic parameters were calculated by the Judd-Ofelt theory. The intensity parameters of the Nd:LuYGdVO₄ crystal were Ω₂ = 9.736 × 10⁻²⁰ cm², Ω₄ = 4.179 × 10⁻²⁰ cm², Ω₆ = 8.020 × 10⁻²⁰ cm² and the stimulate emission cross section was 5.3 × 10⁻¹⁹ cm². Diodepumped actively Q-switched and passively Q-switched Nd:LuYGdVO₄ and Nd:Lu_0.14Y_0.86VO₄ lasers at 1.06 μm were demonstrated. The results indicate that, for both actively and passively Q-switched lasers, the Nd:LuYGdVO₄ lasers can generate shorter pulse width with higher peak power than the Nd:Lu_0.14Y_0.86VO₄ lasers at the same cavity conditions.     

Inelastic partial cross sections for scattering of HF by neon

An analytic expression of the potential energy surface (PES) of the ground state of the Ne-HF complex is obtained by utilizing nonlinear least square method to fit the intermolecular interaction energies [Zhang Y. Guizhou Science, 2003, 21(3): 9–13 (in Chinese)], which have been computed using the augmented correlation-consistent polarized quadruple zeta basis set aug-cc-pVQZ at the theoretical level of CCSD (T). On the basis of the PES, the partial cross sections (PCSs) at the incident energies of 60, 75, 100 and 150 meV for collisions between Ne atoms and HF molecules are calculated using the quantum close coupling approach. The effects of the long-range attractive and the short-range anisotropic interactions on the inelastic PCSs are discussed in detail. The results show: (1) The long-range attractive well of the EPS makes the significant contribution to the lower excitation PCSs, especially the tail maximum for j = 0→j′ = 1 transitions, whereas no contribution is to the j′⩾3 inelastic transitions. (2) The short-range (the repulsive and attractive) interaction makes the significant contribution to the lower excitation PCSs, especially the main peak for j = 0→j′ = 1, 2. As for the transitions of j′⩾3, the short-range interaction plays a key role in the inelastic excitation. (3) Although the positions of the maximums and minimums of the inelastic PCSs are different at the collision energies, they correspond to almost the same impact parameter. Supported by the National Natural Science Foundation of China (Grant Nos. 10676025 and 10574096)     

An X-ray imaging device based on a GEM detector with delay-line readout

An X-ray imaging device based on a triple-GEM (Gas Electron Multiplier) detector, a fast delay-line circuit with 700 MHz cut-off frequency and two dimensional readout strips with 150 μm width on the top and 250 μm width on the bottom, is designed and tested. The localization information is derived from the propagation time of the induced signals on the readout strips. This device has a good spatial resolution of 150 μm and works stably at an intensity of 105 Hz/mm2 with 8 keV X-rays.     

Effect of particle size on the photochromic response of PWA/SiO2 nanocomposite

A series of photochromic phosphotungstic acid (PWA)/SiO₂ composites were synthesized using the sol-gel method. Depending on the feeding schedule of PWA during synthesis, the size of the formed PWA/SiO₂ particles varied considerably from as small as 1.2 nm to ca. 10 nm. With decreasing silica particle size, the total contact area/interaction between SiO₂ and PWA increases, as revealed by FT-IR and solid-state ²⁹Si-NMR analyses. Particularly, when the size of PWA/SiO₂ is ~1 nm, crystallization of PWA is inhibited, and PWA presents as amorphous molecular entities distributing uniformly in the SiO₂ host, which is in evidence in the XRD spectroscopy and HR-TEM imaging. In contrast, substantial crystallization of PWA takes place when PWA/SiO₂ particles are as large as 10 nm, in which case less amount of surface free Si-OH is available for PWA to make bonds with. Photochromism occurs activated by ultraviolet light irradiation. The rate of coloration/bleaching is found to depend strongly on the particle size of PWA/SiO₂; specifically, the rate increases twice when the particle size is reduced from 10 nm to 1.2 nm.     

Evaluation of natural recharge of Chingshui geothermal reservoir using tritium as a tracer

Naturally existing tritium in groundwater was applied as a tracer to evaluate the natural recharge of the Chingshui geothermal reservoir. The residence time (or, age) of Chingshui geothermal water was first determined with tritium data at 15.2 and 11.3 year using the plug flow and dispersive model, respectively. The annual natural recharge was then estimated by combining the use of the residence time and the fluid-in-place of the Chingshui geothermal reservoir. The natural recharge for Chingshui geothermal reservoir was estimated at 5.0 × 10⁵ and 6.7 × 10⁵ m³ year^?1 using the plug flow and dispersive model, respectively. Chingshui geothermal water is largely from a fractured zone in the Jentse Member of the Miocene Lushan Formation. The dispersive model more adequately represents the fracture flow system than the simple plug flow model.