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We propose a silicon strip waveguide structure with alumina thin-film coating in-between the core and the cladding for group-velocity dispersion tailoring. By carefully designing the core dimension and the coating thickness, a spectrally-flattened near-zero anomalous group-velocity dispersion within the telecom spectral range is obtained, which is predicted to significantly broaden the bandwidth of four-wave mixing. We validate this by characterizing the wavelength conversion in a waveguide sample by atomic layer deposition technology, which to our best knowledge is the first experimental demonstration of the proposed structure. Due to the alumina thin-film coating, the wavelength conversion bandwidth reaches $58\,\mathrm{nm}$, an increase by a factor of 1.3 compared to the corresponding structure without coating. This method can also be applied to other material platforms and applications requiring accurate group-velocity dispersion control.

In this paper, an efficient domain decomposition (DD) technique is originally introduced into the unconditionally stable Crank-Nicolson finite-difference time-domain (CN-FDTD) method for analyzing the extraordinary optical transmission (EOT) phenomenon of periodic metallic gratings. Being caused by the evanescent waves propagating along the metal-dielectric interface in the visible and near infrared regions, the dispersion of the considered metal in this case is expressed by the Drude model and solved with a generalized auxiliary differential equation (ADE) technique. The periodic boundary condition is applied to the two-dimensional periodic metallic grating structures due to their periodicity. Then, the standard unsplit-field perfectly matched layer is derived as the absorbing boundary condition for CN-FDTD based on the ADE concept. In DD structures, the whole computational domain is divided into several subdomains to reduce the matrix size and save calculating time. Furthermore, the reverse Cuthill-Mckee scheme for the lower-upper decomposition is applied to the subdomain matrices individually to improve the efficiency of DD-CN-FDTD. Finally, two numerical examples are calculated and the physical mechanism of the EOT phenomenon is investigated. The results from the proposed method demonstrate its accuracy and efficiency for the nanostructures.

In this paper, the Newmark-Beta algorithm is introduced into the finite-difference time-domain (FDTD) method in dispersion media, resulting in an unconditionally stable method for periodic metallic grating analysis. The proposed method eliminates the Courant-Friedrich-Levy constraint and improves the simulation efficiency for multiscale problems. The dispersion of the metal, which is caused by the evanescent waves propagating along the interface between the metal and dielectric materials in the visible and near-infrared regions, is solved with a generalized auxiliary differential equation (ADE) technique. The extraordinary optical transmission through a periodic metallic grating with different number and different size of the perpendicular bump is also investigated. Compared with the traditional ADE-FDTD method and ADE alternating-direction-implicit FDTD method, the results from the proposed method show its accuracy and efficiency.

In this paper, a frequency-dependent locally one-dimensional finite-difference time-domain (LOD-FDTD) method is developed for the extraordinary optical transmission (EOT) analysis of periodic metallic gratings. The dispersion of the metal, caused by the evanescent waves propagating along the interface between the metal and the dielectric materials in the visible and near infrared regions, is expressed by the Drude model and solved with a generalized auxiliary differential equation (ADE) technique. With efficient preprocessing for the lower-upper (LU) decomposition in ADE-LOD-FDTD, the periodic boundary condition (PBC) is applied to the 2-D metallic grating structure. Two numerical examples with different subwavelength slits are calculated, and the mechanism of the EOT phenomenon is investigated. Compared with the standard ADE-FDTD method, the results from the proposed method show its good efficiency for the nanostructures.