Microring resonator composed of vertical slot waveguides with minimum polarization mode dispersion over a wide spectral range.

This paper proposes the design of a vertical slot waveguide-based optical ring resonator on a silicon photonic platform with minimized polarization mode dispersion (PMD) in the presence of waveguide dispersion over a wide band. Slot waveguides provide more degrees of freedom in the design, thereby achieving the minimum PMD over the communication wavelengths. The minimum PMD leads to nearly identical accumulated phase in the optical ring resonator for quasi-TE and TM modes, and thus the resonant wavelength mismatch between the quasi-TE and TM modes can be minimized from 1510 to 1590 nm.

Nanofluidic refractive-index sensors formed by nanocavity resonators in metals without plasmons.

Nanocavity resonators in metals acting as nanofluidic refractive-index sensors were analyzed theoretically. With the illumination of transverse electric polarized light, the proposed refractive index sensor structure acts as a pure electromagnetic resonator without the excitation of surface plasmons. The reflected signal from the nanocavity resonators can be very sensitive to the refractive index of the fluids inside the nanocavities due to the enhancement of the electric field of the resonant mode inside the cavities. Such a sensor configuration can be a useful tool for probing the refractive index change of the fluid inside the nanocavities using the spectral, angular or intensity interrogation schemes. The wavelength sensitivity of 430 nm/RIU, angular sensitivity of 200-1,000 deg/RIU and intensity sensitivity of 25.5 RIU(-1) can be achieved in the proposed sensor configuration.

Controlling the polarization dependence of dual-channel directional couplers formed by silicon-on-insulator slot waveguides.

The polarization dependence of directional couplers (DC) formed by silicon-on-insulator (SOI) slot waveguides was studied, and its applications as highly efficient polarization beam splitters (PBSs) and polarization-independent directional couplers (PIDCs) were investigated. The coupling lengths for the quasi-TE and quasi-TM modes may vary with the waveguide geometry due to structural birefringence; thus numerical simulations of the coupling effects in the directional couplers with different aspect ratios and waveguide spacing were conducted to obtain the optimal design parameters for high efficiency as well as compact device size. The lengths of the coupling regions of the designed PBS and PIDC are 47.61 and 23.13 µm, respectively, and they delivered good performance, with an extinction ratio greater than 20 and 1 dB bandwidth larger than 100 nm. The tolerance of fabrication error in the practical device is also discussed.

Plasmon field enhancement in silver core-protruded silicon shell nanocylinder illuminated with light at 633 nm.

We show, to the best of our knowledge, the first simulation result of the strong plasmonic field coupling and enhancement at the Ag/Si interface of a silver core/protruded silicon shell nanocylinder by using the finite-element method. The strong plasmon field, with a slow effective phase velocity accumulated at the Ag/Si interface, which results from the large effective index of the surface plasmon due to the nearly identical real parts with opposite signs of the permittivities of silver and silicon at 633 nm, is analyzed. When the silicon shell has shallow protrusions of proper periodicity to meet the phase matching condition between the incident light and the surface plasmon wave at the Ag/Si interface, a higher scattered electric field and a higher sensitivity to the refractive index change of the surrounding medium can be achieved. Furthermore, a feasible implementation of the core-shell nanocylinder design concept is studied and discussed.

Surface plasmon resonance in a hexagonal nanostructure formed by seven core shell nanocylinders.

A hexagonal nanostructure formed by seven core shell nanocylinders filled with different dielectric cores is investigated. The surface plasmon resonance in such a hexagonal nanostructure under conditions of different illumination wavelengths, dielectric cores, angles of incidence, and thicknesses of silver shells is studied by use of the finite element method. Simulation results show that the resonant wavelength is redshifted as the dielectric constant and the size of the core increase. The peak resonant wavelength and the local field enhancement are approximately proportional to the radius of the dielectric core. Additionally, the surface plasmon field excited by TM-polarized light at the incident angle of theta=15 degrees is exactly a linear combination of those excited at incident angles of theta=0 degrees and 30 degrees, confirming the linear nature of the surface plasmon resonance in a nanostructure formed by linear media.