Design and fabrication of GeAsSeS chalcogenide waveguides with thermal annealing

We reported a chalcogenide glass-based rib waveguide fabricated using photolithography and dry etching method. A commercial software(COMSOL Multiphysics) was used to optimize the waveguide structure and the distribution of the fundamental modes in the waveguide based on the complete vector finite component. We further employed thermal annealing to optimize the surface and sidewalls of the rib waveguides. It was found that the optimal annealing temperature for Ge As Se S films is 220℃, and the roughness of the films could be significantly reduced by annealing. The zero-dispersion wavelength(ZDW) could be shifted to a short wavelength around ~2.1 μm via waveguide structural optimization, which promotes supercontinuum generation with a short wavelength pump laser source. The insertion loss of the waveguides with cross-sectional areas of 4.0 μm×3.5 μm and 6.0 μm×3.5 μm was measured using lens fiber and the cut-back method. The propagation loss of the 220℃ annealed waveguides could be as low as 1.9 d B/cm at 1550 nm.

Dual-symmetry-perturbed all-dielectric resonant metasurfaces for high-Q perfect light absorption

We demonstrate a high-Q perfect light absorber based on all-dielectric doubly-resonant metasurface.Leveraging bound states in the continuum(BICs)protected by different symmetries,we manage to independently manipulate the Q factors of the two degenerate quasi-BICs through dual-symmetry perturbations,achieving precise matching of the radiative and nonradiative Q factors for degenerate critical coupling.We achieve a narrowband light absorption with a>600 Q factor and a>99%absorptance atλ_(0)=1550 nm on an asymmetric germanium metasurface with a 0.2λ_(0)thickness.Our work provides a new strategy for engineering multiresonant metasurfaces for narrowband light absorption and nonlinear applications.

UV-light-assisted synthesis of CeB_(6)@Ag nano-trees for SERS application

The conventional methods of using surfactants to synthesize noble metal nanoparticles usually introduce residues on the surface,which inevitably decreases nanoparticles’ surface enhanced Raman scattering(SERS) performance.Herein,we propose a surfactant-free and feasible approach of preparing cerium hexaboride-Ag nano-trees hybrids(CeB_(6)@Ag nano-trees) as the SERS substrate.First,the CeB_(6)was synthesized by a one-pot ionothermal method.Secondly,the CeB_(6)powder and silver nitrate were dispersed in an aqueous solution.Thereafter,the Ag+was reduced by the UV-light assisted photoreaction and deposited on the surface of the CeB_(6).The SERS performance of the CeB_(6)@Ag nano-trees was evaluated by using the Rhodamine 6 G as the Raman reporter.It shows that CeB_(6)@Ag nano-trees exhibit good SERS sensitivity with the enhancement factor of 2.45 × 10^(7) and detection limit of 10^(-10) mol/L.Moreover,uniformity evaluation of the SERS signal intensity on the substrate also shows that relatively good relative standard deviation values of 12.6%(Raman peak@612 cm^(-1)) and 14.1%(Raman peak@1652 cm^(-1))can be achieved.Finally,finite element simulation evidences that excellent SERS performance of the CeB_(6)@Ag nano-trees is produced by the strong coupled localized surface plasmon resonance generated under the Raman laser irradiation.

Dark dimer mode excitation and strong coupling With a nanorod dipole

We theoretically investigate dark dimer mode excitation and strong coupling with a nanorod dipole. Efficient excitation of a dark mode in a gold(Au) nanorod dimer using an electric dipole can be achieved by an optimal overlap between the dipole moment and dark modal field. By replacing the dipole emitter with an Au nanorod, a plane wave excited dipole mode in the nanorod can be effectively coupled to the dark dimer mode through nearfield interaction. At a 10-nm separation of the nanorod and the dimer, plasmonic interaction between dipole-dark modes enters the strong coupling regime with a Rabi-like splitting of 219.2 meV, which is further evidenced by the anticrossing feature and Rabi-like oscillation of electromagnetic energy of the coupled modes. Our results propose an efficient approach to far-field activating dark modes in coupled nanorod dimers and exchanging plasmonic excitations at nanoscale, which may open new opportunities for nanoplasmonic applications such as nanolasers or nanosensors.