**1. Introduction**

The electromagnetic scattering of metals in optical frequency region possesses special characteristics. At these frequencies, there are electron oscillations in the metal called plasmons with distinct resonant frequencies, which produce strongly enhanced near fields at the metal surface. This effect can be analyzed using Lorentz-Drude model of the complex dielectric constant. The science of the electromagnetic optical response of metal nanostructures is known as plasmonics or nanoplasmonics [1, 2].

One subarea of nanoplasmonics is the field of optical nanoantennas, which are metal nanostructures used to transmit or receive optical fields [3–5]. This definition is similar to that of conventional radio frequency (RF) and microwave antennas. The main difference between these two regimes (RF-microwave and optical) is due to physical properties of the metals at optical frequencies where they cannot be considered as perfect conductors because of the plasmonic effects [2]. Comprehensive reviews on optical antennas have been presented in [6–11]. In these works, the authors described recent developments in calculation of such antennas, their applications and challenges in their design. In **Figure 1**, we present some examples of fabricated nanoantennas.

Yagi-Uda and dipole. The numerical analysis is performed by the method of moments (MoM) [18] and the finite element method (FEM) through the software COMSOL Multiphysics [19]. In this analysis, the transmission power and the near electric field are investigated for three nanolinks: Yagi-Uda/dipole, Yagi-Uda/ Yagi-Uda and dipole/dipole. This work is organized as follow: Section 1 is the introduction, Section 2 presents the description of nanolinks, Section 3 presents the numerical model used in the analysis, Section 4 contain the numerical results, and

*Wireless Optical Nanolinks with Yagi-Uda and Dipoles Plasmonic Nanoantennas*

In this work, three models of nanolinks are proposed and analyzed. The first is

The geometry of the Yagi-Uda/dipole nanolink is presented in **Figure 2**, where a voltage source *VS* excites the left nanoantenna, which functions as a transmitter (Yagi-Uda) and the right nanoantenna that acts as a receptor (dipole), connected to load impedance *ZC*. The nanolink is located in the free space and is formed by cylindrical conductors of gold. The complex permittivity of this material is represented by the Lorentz-Drude model of Au [11]. The Yagi-Uda transmitting nanoantenna is composed of a dipole, a reflector and three directors (**Figure 1** left). The dipole of the transmitter, located in the *z* = 0 plane along the *x*-axis and centered at the origin, has total length 2*hdT* + *ddT*, radius *adT* and voltage gap *ddT*. The reflector has *hr* length and *ar* radius. The directors have the same length *hd* and radius *ad*. The parameters *dhr* and *dhd* are the distances between reflector and directors element to Yagi-Uda antenna, respectively (**Figure 1** left). The receiver antenna is a dipole (**Figure 1** right), located in the *z* = 0 plane and displaced at a *dTR* relative to the dipole axis of the transmitting antenna, with total length 2*hdR* + *ddR*,

a nanolink formed by dipole/dipole antennas (**Figure 2**, without reflector and directors), the second by Yagi-Uda/dipole antennas (**Figure 2**) and the third by Yagi-Uda/Yagi-Uda antennas (**Figure 2**, with the receiving antenna equal to the

radius *adR*, gap length *ddR* and load *ZC* connected to its gap.

*Geometry of the nanolink composed by a Yagi-Uda antenna (transmitter) and a nanodipole (receiver).*

Section 5 are the conclusions.

*DOI: http://dx.doi.org/10.5772/intechopen.88482*

**2. Description of nanolinks**

transmitting antenna).

**Figure 2.**

**3**

#### **Figure 1.**

*(a) Scanning electron micrographs of various optical nanoantennas. (b) Application example of Yagi-Uda nanoantennas in wireless optical nanolink, where the nanoantennas perform transduction between electrical current and optical radiation [5].*

Optical nanoantennas have received great interest in recent years in the scientific community due to their ability to amplify and confine optical fields beyond the light diffraction limit [6]. With this characteristic, it is possible to apply in several areas, such as nanophotonics, biology, chemistry, computer science, optics and engineering, among others [6, 7, 12]. In addition, these studies were expanded due to the development of computational numerical methods and innovations in nanofabrication techniques, such as electron beam lithography, colloidal lithography and ion beam lithography [9].

Optical wireless nanolinks with nanoantennas can be used to efficiently communicate between devices, significantly reducing the losses that occur in wired communication. Nanolinks with different geometries of nanoantennas were investigated in the literature [13–17]. In [13] the authors propose a broadband nanolink formed by dipole-loop antennas. The results showed that using this nanolink with dipole-loop antennas instead of conventional dipoles, it is possible to increase the operating bandwidth of the system to the range of 179.1–202.5 THz, which is within the optical range of telecommunications. In [14], a wireless nanolink formed by dipole antennas is compared to a wired nanolink formed by a waveguide, the study showed that the wireless link may work better than a plasmon waveguide in sending optical signal in nanoscale from one point to another, from a certain distance. In [15], a nanolink Yagi-Uda chip directives are proposed, the results show that the use of directional antennas increases the energy transfer (power ratio) and link efficiency, minimizing interference with other parts of the circuit. In [16], it is presented another wireless nanolink application formed by a transmitting nanoantenna Vivaldi and another receiver, to be used in chip, with that nanolink a high gain and bandwidth covering the entire spectrum of the C band of telecommunications. In [17], broadband nanolinks were analyzed using horn and dipole type optical nanoantennas, where the horn antenna had better performance, because better energy transfer at the nanolink and greater bandwidth were obtained in relation to the dipole link. These studies used identical transmitting and receiving antennas, and showed the feasibility of using wireless communication in the nanophotonics.

In this work, we present a comparative analysis of nanolinks formed by equal and different transmitting and receiving nanoantennas. The antennas used are

*Wireless Optical Nanolinks with Yagi-Uda and Dipoles Plasmonic Nanoantennas DOI: http://dx.doi.org/10.5772/intechopen.88482*

Yagi-Uda and dipole. The numerical analysis is performed by the method of moments (MoM) [18] and the finite element method (FEM) through the software COMSOL Multiphysics [19]. In this analysis, the transmission power and the near electric field are investigated for three nanolinks: Yagi-Uda/dipole, Yagi-Uda/ Yagi-Uda and dipole/dipole. This work is organized as follow: Section 1 is the introduction, Section 2 presents the description of nanolinks, Section 3 presents the numerical model used in the analysis, Section 4 contain the numerical results, and Section 5 are the conclusions.
