In this paper, we have utilized Au nanoring chains in an ${\mathrm{SiO}}_2$ host to design certain $\mathbf{T}$-and $\mathbf{Y}$-structures, and expanded it to transport and split the electromagnetic energy in integrated nanophotonic devices operating at an optical communication band ($\lambda \approx 1550\mathrm{nm}$). We compared two structures and tried to choose the best one, with lower losses and higher efficiency at the output branches, in order to split and transport the optical energy. Comparing the different types of nanoparticles corroborates that nanorings have an extra degree of tunability in their geometrical components. Meanwhile, nanorings show strong confinement in near-field coupling, less extinction coefficient, and also lower scattering into the far field during energy transportation at the C-band spectrum. Due to the nanoring’s particular properties, transportation losses would be lower than in other nanoparticle-based structures like nanospheres, nanorods, and nanodisks. We demonstrate that Au nanorings surrounded by an ${\mathrm{SiO}}_2$ host yield suitable conditions to excite surface Plasmons inside the metal. Comparison between $\mathbf{Y}$-and $\mathbf{T}$-splitters shows that the $\mathbf{Y}$-splitter is a more suitable alternative than the $T$-splitter, with higher transmission efficiency and lower losses. In the $\mathbf{Y}$-structure, the power ratio (time-averaged power across the surface) is 24.7%, and electromagnetic energy transportation takes place at group velocities in the vicinity of 30% of the velocity of light; transmission losses are $\gamma T=3\mathrm{dB}/655\mathrm{nm}$ and $\gamma T=3\mathrm{dB}/443\mathrm{nm}$. In this work, we have applied the finite-difference time-domain method (FDTD) to simulate and indicate the properties of structures.

In this article, a novel graphene based Optical tweezer (OT) and size based particle sorter is proposed and numerically investigated by finite difference time domain (FDTD) method and Maxwells stress tensor (MST) analysis. Each unit cell of the structure is composed of a graphene layer on top a metallic nano-ring which is embedded in SiO2. Strong hotspots with field enhancements reaching values as high as 140 are obtained inside the rings with no need to sharp edges conventional in plasmonic structures. Size based trapping can be achieved by controlling the fermi energy of the graphene through a gate. By cascading several unit cells, each operating at a different gate voltage, a particle size based sorter is designed which can effectively sort Polystyrene particles with their diameter in the range of smaller than 10 nm to 100 nm. The structure is illuminated by a laser beam in the mid-IR frequency range of 4-8 m and its wavelength and intensity are kept constant even for sorting functionality. Instead, tunable plasmonic characteristics of graphene is utilized for active particle sorting. The fermi level-particle size-gate voltage relationship of the proposed OT is fully investigated at the article. Moreover, it is shown that the proposed structure is capable of sorting particles according to their refractive indices as well.

Photothermal therapy using nanoparticles is a prominent technique for cancer treatment. The principle is to maximize the heat conversion efficiency using plasmonic nanoparticle–light interaction. Due to their unique optical characteristics derived from their anisotropic structure, gold nanostars (GNSs) have gotten significant attention in photothermal therapy. To design a proper cancer treatment, it is vital to study the thermal effect induced close to the gold nanoparticles, in the vicinity, and the cancerous tissue. A temperature-dependent 2D model based on finite element method models is commonly used to simulate near-IR tumor ablation. The bioheat equation describes the photothermal effect within the GNSs and the environment. Surface cooling and heating strategies, such as the periodical heating method and a reduced laser irradiation area, were investigated to address surface overheating problems. We also determined that the optimal laser radius depends on tumor aspect ratio and laser intensity. Our results provide guidelines to evaluate a safe and feasible temperature range, treatment time, optimal laser intensity, and laser radius to annihilate a tumor volume.

All-optical graphene-based optical modulators have recently attracted much attention because of their ultrafast and broadband response characteristics (bandwidth larger than 100 GHz) in comparison with the previous graphene-based optical modulators, which are electrically tuned via the graphene Fermi level. Silicon photonics has some benefits such as low cost and high compatibility with CMOS design and manufacturing technology. On the other hand, graphene has a unique large nonlinear Kerr coefficient, which we calculate using graphene’s tight-binding model based on the semiconductor Bloch equations. Its real and imaginary parts are negative at the wavelength of 1.55 µm and E F = 0.1 e V . To simultaneously use the benefits mentioned above, we present an all-optical, CMOS-compatible, and graphene-on-silicon slot (GOSS) waveguide extinction and phase modulator that consists of two different geometries. The first one consists of a one-stage GOSS waveguide with a single layer of graphene. To increase the light–graphene interaction and consequently enhance the modulation efficiency (ME), another stage of the GOSS waveguide is placed over the first one. This two-stage configuration is called a graphene-on-silicon double-slot (GOSDS) waveguide. The ME, insertion loss (IL), and modulation depth (MD) for a 12.5 µm GOSDS waveguide modulator with a double layer of graphene can reach 0.241 dB/µm, 1.31 dB, and 77%, respectively, at optical pump intensities about 9 M W c m − 2 . Our design has a smaller waveguide length (17.6 times) than the previous all-optical graphene-on-silicon ribbon waveguide extinction modulator and high MD (about 2 times) in comparison with a graphene-clad microfiber all-optical extinction modulator. Compared with an all-optical Mach–Zehnder interferometer phase modulator, our design has short graphene coated waveguide length ( ≈ 0.1 times) and low local optical intensities ( ≈ 0.043 times) needed for π phase shift. This study may promote the design and realization of high-performance, wideband, compact, and all-optical control on a single chip with a reasonable contrast level.