Shrinking the linewidth of resonances induced by multiple coupled resonators is comprehensively analyzed using the coupled-mode theory (CMT) in time. Two types of coupled resonators under investigation are coupled resonator optical waveguides (CROWs) and side-coupled resonators with waveguide (SCREW). We examine the main parameters influencing on the spectral response such as the number of resonators (n) and the phase shift (φ) between two adjacent resonators. For the CROWs geometry consisting of n coupled resonators, we observe the quality (Q) factor of the right- and left-most resonant lineshapes increases n times larger than that of a single resonator. For the SCREW geometry, relying on the phase shift, sharp, and asymmetric resonant lineshape of the high Q factor a narrow linewidth of the spectral response could be achieved. We employ the finite-difference time-domain (FDTD) method to design and simulate two proposed resonators for practical applications. The proposed coupled resonators in silicon-on-insulator (SOI) slotted two-dimensional (2-D) photonic crystals (PhCs) filled and covered with a low refractive index organic material. Slotted PhC waveguides and cavities are designed to enhance the electromagnetic intensity and to confine the light into small cross-sectional area with low refractive index so that efficient optical devices could be achieved. A good agreement between the theoretical CMT analysis and the FDTD simulation is shown as an evidence for our accurate investigation. All-optical switches based on the CROWs in the SOI slotted 2-D PhC waveguide that are filled and covered by a nonlinear organic cladding to overcome the limitations of its well-known intrinsic properties are also presented. From the calculations, we introduce a dependency of the normalized linewidth of the right-most resonance and its switching power of the all-optical switches on number of resonator, n. This result might provide a guideline for all-optical signal processing on a silicon PhC chip design.
The concept of broadband extraordinary optical transmission (EOT) through metallic gratings at the plasmonic Brewster
angle has recently been introduced. It is based on the ultrabroadband impedance matching between guided modes
supported by ultranarrow slits in a one-dimensional (1D) metallic grating and an incident transverse magnetic (TM)
wave. The overall mechanism results in total transmission through such a corrugated plasmonic screen. This concept was
first demonstrated in 1D metallic gratings and it can also be extended to two-dimensional (2D) periodic metallic gratings
made by either multiple rectangular or cylindrical rods. In this contribution, we review this concept and we demonstrate
that this phenomenon can be applied to semiconductor gratings, whose materials have plasmonic properties at THz
frequencies. This may open several opportunities to develop low-loss, broadband optical metamaterials for energy
harvesting and concentrators.