S. S. A. Obayya

Super directive Yagi–Uda nanoantennas with an ellipsoid reflector for optimal radiation emission

In this paper, the optimal designs of silicon Yagi–Uda nanoantennas (NAs) with an ellipsoid reflector have been proposed and analyzed using the 3D finite-difference time-domain method. The combination of nanospheres, nanowires, and ellipsoid reflectors has been employed to enhance the antenna directivity. The nanoantenna geometrical parameters are optimized using the particle swarm optimization algorithm. The optimized spherical NA with an ellipsoid reflector shows high directivity of 19.89, which is higher than the conventional counterpart by 65.75%. This enhancement is attributed to the different supported modes by the ellipsoid reflector, which increases the forward radiation and suppresses the backward one. Further, the optimized nanowire design with an ellipsoid reflector has achieved a directivity of 23.4. In addition, the radiation efficiency has been increased to 80.2% and 75.9% for optimized spherical and nanowire antennas, respectively. This enhancement is attributed to the efficient coupling between array elements as well as reduced sidelobe and back-lobe levels.

Novel Gradient Smoothing Method-Based Time Domain Beam Propagation Analysis of Optical Integrated Circuits

Novel gradient smoothing method (GSM) is adopted for time domain beam propagation method. GSM uses unstructured mesh and no Galerkin procedure is required. It is utilized to simulate various integrated circuits.

Introduction to Silicon Photonics

This chapter reviews the fundamentals of the silicon on insulator (SOI) technology due to its advantages. The chapter starts with an introduction to the SOI followed by the different waveguides based on the SOI technology and their advantages. Further, the novel platforms that have been recently emerging beside the SOI are also presented. Finally, various fabrication processes for performing the SOI wafer are introduced in more detail.

Introduction to Optical Waveguides

This chapter presents an introduction to the optical waveguides including planar and nonplanar structures. Additionally, an analysis of planner waveguides based on ray-optical approach and Maxwell’s equations approach is investigated. In this context, types of modes, dispersion, cutoff frequency, and effective thickness of the optical waveguides are discussed thoroughly. Further, the different numerical techniques and their based mode solvers which are used to analyze optical waveguides are summarized in brief. Finally, the coupling mechanisms to the optical waveguide are introduced including transversal coupling techniques and the longitudinal coupling techniques.

Basic Principles of Biosensing

Recently, optical sensors have been improved extensively due to the rising need of sensing applications in different specialties such as, medicine, military, environment, food quality control. The improvement of the photonic technologies based on the CMOS compatible silicon-on-insulator (SOI) and photonic crystal structures improves the sensing performance significantly. This chapter presents the basic principles of the sensing process. Additionally, it introduces the different configurations of optical sensors based on working principle, sensor design, and detection purpose.

Temperature Sensors Based on Plasmonic Photonic Crystal Fiber

In this chapter, two novel highly sensitive surface plasmon resonance photonic crystal fiber (PCF) temperature sensors based on liquid crystal (LC) or alcohol mixture are presented and studied. Through this chapter, the coupling characteristics between the core-guided mode inside the PCF core infiltrated with either nematic LC or alcohol mixture and surface plasmon mode around the surface of nanogold wire are studied in detail. The structural geometrical parameters of the proposed designs, such as hole pitch, number of metallic rods, core diameter, and metallic rod diameter, are optimized to achieve highly temperature sensitivity. The suggested alcohol-based sensor offers high sensitivity of 3 nm/°C and 4.9 nm/°C for transverse electric (TE) and transverse magnetic (TM) polarizations, respectively. Moreover, the alcohol core sensor operates over a wider range of temperatures from −4 °C to 53 °C. In addition, the suggested LC-based sensor of compact device length of 20 μm proved to surpass the sensitivity of the recent temperature sensors. Using the LC instead of alcohol has improved the sensitivity to 10 nm/°C. The results are calculated using full-vectorial finite-element method with irregular meshing capabilities and perfect matched layer boundary conditions.

Multifunctional Plasmonic Photonic Crystal Fiber Biosensors

In this chapter, two novel designs of compact surface plasmon resonance multifunctional biosensors based on nematic liquid crystal (NLC) and Alcohol mixture photonic crystal fibers (PCFs) are proposed and studied. The suggested sensors have a central hole filled either with NLC or alcohol mixture as temperature-dependent materials. Further, another large hole filled with liquid analyte has a gold nanorod as a plasmonic material. Therefore, the proposed sensors can be used for temperature and analyte refractive index sensing via the coupling between the core-guided modes in the central hole and the surface plasmon modes around the gold nanorod. The effects of the structure geometrical parameters are studied to maximize the sensitivity of the PCF biosensors. The numerical analysis is carried out using full-vectorial finite element method with perfectly matched layer boundary conditions. The reported multifunctional NLC-based sensor offers high sensitivity of 5 nm/°C and 3700 nm/RIU (refractive index unit) for temperature and analyte refractive index sensing, respectively. In addition, the alcohol mixture PCF sensor achieves high-temperature sensitivity of 13.1 nm/°C with high analyte refractive index sensitivity of 12700 nm/RIU. To the best of the authors’ knowledge, it is the first time to introduce PCF biosensor with high sensitivity for temperature and analyte refractive index sensing as well. Further, the achieved sensitivity values of the alcohol sensor are far higher than those reported in the literature.

Finite Element Method for Sensing Applications

In this chapter, the fundamentals of the nodal finite element method (FEM) are presented, including the first-order element and second-order element. The nodal FEM is introduced for the scalar concept of the propagation constant of 2D waveguide cross section. Then, it is extended to include the time domain analysis under perfectly matched layer absorbing boundary conditions. A simple sensor based on optical grating is thereafter simulated using the time domain FEM. Also, the full vectorial analysis is discussed through the application of the penalty function method on the nodal FEM and the vector finite element method (VFEM). For the penalty function method, a global weighting factor is used to incorporate the effect of the divergence-free equation. In the VFEM, nodes are used to represent the orthogonal component of the field while the edges are used to represent the tangential component for accurate application of the boundary conditions. Finally, surface plasmon resonance photonic crystal fiber biosensor is introduced as an example of the full vectorial analysis using the VFEM.

Basic Principles of Surface Plasmon Resonance

In this chapter, the basic concept concerning the surface plasmon phenomena is presented. Different types of surface plasmon wave (localized and propagating) are reviewed. Moreover, the thin metallic film surface plasmon waveguide is analyzed in order to show the symmetric and asymmetric modes. Finally, other types of surface plasmon waveguides are discussed to show the trade-off between the confinement of the field profile and the attenuation loss.

Silicon Nanowires for DNA Sensing

Highly sensitive hybrid plasmonic slot waveguide (HPSW) biosensors based on silicon on insulator (SOI) are proposed and analyzed for DNA hybridization detection. The reported designs are based on increasing the light interaction with the sensing region by using slot waveguide with plasmonic material. Due to the high index contrast and plasmonic effect, an ultrahigh optical confinement is achieved in the low-index regions which enables the detection of the smallest change in the analyte refractive index with high sensitivity. The normalized power confinement, power density, effective index of the supported modes by the HPSWs are analyzed to achieve high power confinement through the suggested biosensors, and hence, high sensitivity can be obtained. The HPSWs are also incorporated with straight slotted resonator to calculate the sensitivity of the proposed design. In this study, two different plasmonic materials (gold and titanium nitride) are used for the proposed designs. The simulation results are calculated using full vectorial finite element method (FVFEM). The reported biosensors have high sensitivity of 1890.4 nm/RIU (refractive index unit) with a detection limit of 2.65 × 10−6 RIU with gold material and 1190 nm/RIU with a detection limit of 4.2 × 10−6 RIU based on titanium nitride material, which are the highest in the literature to the best of our knowledge.