<p>We propose, simulate, and achieve a method of realization of all-optical reversible logic gates based on nanoring dielectric-metal-dielectric plasmonic waveguides at 1550 nm and in the same structure. Finite-element method was used to study and simulate the proposed plasmonic reversible logic gates. These reversible logic gates are wire, NOT, swap, and Feynman. The working principle of the proposed reversible gates is based on the interferences (destructive or constructive) between the light that propagates in the input signal port(s) and control signal port(s). The threshold value of transmission between OFF and ON states is proposed as 0.4. Finally, the designed area of the proposed structure is very small (300 nm × 460 nm). These plasmonic reversible gates can contribute in construction of nanophotonic reversible logic circuits and all-optical quantum computing.</p>
We propose, analyze, and simulate a configuration to realize all-optical logic gates based on nanoring insulator–metal–insulator (IMI) plasmonic waveguides. The proposed plasmonic logic gates are numerically analyzed by finite element method. The analyzed gates are NOT, OR, AND, NOR, NAND, XOR, and XNOR. The operation principle of these gates is based on the constructive and destructive interferences between the input signal(s) and the control signal. The suggested value of transmission threshold between logic 0 and logic 1 states is 0.25. The suggested value of the transmission threshold achieves all seven plasmonic logic gates in one structure. We use the same structure with the same dimensions at 1550-nm wavelength for all proposed plasmonic logic gates. Although we realize seven gates, in some cases, the transmission of the proposed plasmonic logic gates exceeds 100%, for example, in OR gate (175%), in NAND gate (112.3%), and in XNOR gate (175%). As a result, the transmission threshold value measures the performance of the proposed plasmonic logic gates. Furthermore, the proposed structure is designed with a very small area (400 nm × 400 nm). The proposed all-optical logic gates structure significantly contributes to the photonic integrated circuits construction and all-optical signal processing nanocircuits.
It is shown that fork-shaped plasmonic gratings can display a hybrid mode that features both plasmonic mode (TMmode) and dielectric mode (TE-mode) characteristics with wide range of tunable group velocities. A dielectric gap is
introduced in the middle of metallic grating and it is found that this gap plays an important role in controlling the TE-TM
mode coupling. By controlling the polarization angle we can switch from plasmonic mode to dielectric mode. Thus, a
new scheme for manipulating the optical confinement by using a polarizer is realized. (see Figure) We can combine the
plasmonic mode and dielectric mode to reduce the intrinsic loss of Plasmon-polariton due to the free-carrier absorption
in the conducting material with the same degree of confinement. The fork structure provides an easier way to control the
group velocity in a wide range. The dispersion relations were calculated by using Rigorous Coupled Wave Analysis. We
obtain tunable group velocities ranging from 0.2<i>c</i> to almost zero (i.e. achieving localized Surface Plasmon-polariton) and from 0.05<i>c</i> to 0.3<i>c</i> by varying the pillar and dielectric (made of Si<sub>3</sub>N<sub>4</sub>) thicknesses respectively. This fork structure is expected to have applications in surface plasmon polariton (SPP) mixed with guided-mode based optical devices, such as optical buffering, hybrid waveguides, splitters and lasers and especially for applications requiring slow light propagation.
We study plasmonic cavity in a 1D array of asymmetric T-shaped plasmonic gratings. The asymmetric T-shaped
plasmonic grating contains a silver bigrating structure. The first metallic grating contains the post of the T-shaped
structure embedded in SiO2 and the second metallic grating is the cap of the T-shaped structure embedded in air. The
bigrating can open a large plasmonic band gap (~ 0.15eV). We introduce a defect in a 1D array of asymmetric T-shaped
structure by reducing the width of the cap in one line or in multiple lines. We have studied two kinds of defects. The first
defect is a missing line from the T-shaped grating and it has a relatively low quality factor of 64 and a very small
effective mode area [0.026 (λ/n)<sup>2</sup>]. The second one is done by removing or shifting more than one line from the T-shaped
grating to make a gentler confinement and it leads to an enhancement of the quality factor (~200) and a slight increase in
the effective mode area to [0.0375 (λ/n)<sup>2</sup>].
We study plasmon-polariton band structures theoretically for T-shaped plasmonic gratings. We analyze the structure
using Fourier expansion and perform numerical simulation using Rigorous Coupled Wave Analysis (RCWA). A detailed
derivation of equations which can be used to control the momentum gap behaviour using Fourier transform is given. A
structure gap is introduced in the post of the T-shaped plasmonic grating and it is found that the size of this gap plays an
important role in controlling the plasmon-polariton band gap and group velocities. We have found that the plasmon
mode can be decupled with light when the upper post is displaced by half a period. Thus, such a structure can be used as
plasmonic decupler. Furthermore, by displacing the T-shaped post we can tune the plasmon-polariton band gap and
group velocity in a non-monotonic manner. We obtain energy band gaps ranging from 0.4eV to 0eV by changing the size
of the structure gap from 0 to 330 nm and from 0.115eV to 0.068eV by displacing the post of the T-shaped structure
from 0 to 500 nm. We also obtain tunable group velocities ranging from one to several orders of magnitude smaller
than the speed of light in the vacuum. This asymmetric T-shaped plasmonic grating is expected to have applications in
surface plasmon polariton (SPP) based optical devices, such as filters, waveguides, splitters and lasers, especially for
applications requiring large photonic band gap.