Mohamed Farhat O. Hameed

Label-Free Highly Sensitive Hybrid Plasmonic Biosensor for the Detection of DNA Hybridization

A highly sensitive hybrid plasmonic slot-waveguide (HPSW) biosensor based on silicon-on-insulator is proposed and analyzed for DNA hybridization detection. The reported design is 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, and effective index of the supported modes by the HPSW are analyzed to achieve high-power confinement through the suggested biosensor and hence high sensitivity can be obtained. The HPSW is also incorporated with straight slotted resonator to calculate the sensitivity of the proposed design. The simulation results are calculated using full vectorial finite element method. The reported biosensor has high sensitivity of 1890.4 nm/RIU (refractive index unit), which is the highest in the literature to the best of our knowledge with a detection limit of 2.65 × 10 –6 RIU.

Detection of DNA hybridization by hybrid alternative plasmonic biosensor

In order to detect DNA hybridization with label free and high sensitivity, a hybrid alternative plasmonic slot waveguide (HAPSW) biosensor based on silicon-on-insulator (SOI) is proposed and analyzed. The reported design increases the light interaction with the sensing region by using a slot-waveguide along with titanium nitride as an alternative plasmonic material. The suggested biosensor can detect the slightest change in the analyte refractive index with high sensitivity due to an ultra-high optical confinement in the low-index regions caused by the high index contrast and plasmonic enhancement. The effective index, normalized power confinement, and sensitivity are analyzed for the detection of the DNA hybridization. The simulation results are obtained using full vectorial finite element method (FVFEM). The suggested biosensor has high sensitivity of 1190 nm/RIU (refractive index unit) for DNA hybridization detection, which is very high relative to those reported in the literature to the best of our knowledge.

Recent Trends in Plasmonic Nanowire Solar Cells

Light trapping is crucial for low-cost and highly efficient nanowire (NW) solar cells (SCs). In order to increase the light absorption through the NWSCs, plasmonic materials can be incorporated inside or above the NW design. In this regard, two novel designs of plasmonic NWSCs are reported and analyzed using 3D finite difference time domain method. The geometrical parameters of the reported designs are studied to improve their electrical and optical efficiencies. The ultimate and power conversion efficiencies (PCE) are used to quantify the conversion efficiency of the light into electricity. The first design relies on funnel shaped SiNWs with plasmonic core while the cylindrical NWs of the second design are decorated by Ag diamond shaped. The calculated ultimate efficiency and PCE of the plasmonic funnel design are equal to 44% and 18.9%, respectively with an enhancement of 43.3 % over its cylindrical NWs counterpart. This enhancement can be explained by the coupling between the three optical modes, supported by the upper cylinder, lower cone and plasmonic material. Moreover, the cylindrical SiNWs decorated by Ag diamond offer an ultimate efficiency and short-circuit current density of 25.7%, and 21.03 mA∕cm2, respectively with an improvement of 63% over the conventional cylindrical SiNWs.

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.

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.

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.

Silicon nanowires with an alternative plasmonic material for highly efficient light trapping

In this study, the absorption capabilities of a plasmonic funnel-shaped silicon nanowire (SiNW) solar cell is introduced and analyzed by using 3D finite difference time domain method (FDTD). The reported NW design has titanium nitride (TiN) core as an alternative plasmonic material. The different geometrical parameters of the reported design are studied to maximize the absorption and hence the ultimate efficiency. An ultimate efficiency and short-circuit current density Jsc of 48.3% and 38.98 mA/cm2, respectively are obtained which are greater than the conventional Si-Funnel counterpart by 46.36%. The enhancement of the light absorption is attributed to the combination between different types of optical modes and plasmonics modes of the funnel-shaped NW and the TiN, respectively.

Highly efficient multiplexer demultiplexer based on liquid crystal channels

A novel design of multiplexer-demultiplexer (MUX-DEMUX) based on channel waveguide on silicon dioxide (SiO2) is introduced and analyzed. The suggested structure consists of two neighboring channels infiltrated with nematic liquid crystal (NLC) material of type E7. The two channels are etched in the SiO2 substrate. The electro-optic effect of the NLC is used to control the waveguide propagation condition using an external electric field. Additionally, a plasmonic wire is inserted between the two waveguides to enhance the suggested MUX-DEMUX in terms of compactness. The modal analysis of the y-polarized modes supported by the NLC MUX-DEMUX is carried out using full-vectorial finitedifference method (FVFDM). Further, the propagation characteristics through the reported design are obtained using full vectorial finite difference beam propagation method (FVFD-BPM). The design parameters of the NLC MUX-DEMUX have been studied to obtain an efficient waveguide coupling with a short device length. Moreover, the NLC MUXDEMUX has a compact device length of 1296 μm. The numerical results reveal that the reported MUX-DEMUX has a small insertion loss of 8x10-6 dB with a good crosstalk better than -37 dB and -30 dB at the studied wavelengths of 1.3 μm and 1.55 μm, respectively. To the best of the authors’ knowledge, it is the first time to introduce a MUX-DEMUX based on channel on SiO2 platform with a simple design and broadband operation.

Optimization of photonic crystal fiber biosensor by particle swarm algorithm

A hexagonal shape surface plasmon photonic crystal fiber (PCF) biosensor is reported and studied numerically. The proposed design has three identical cores along the y-axis filled with liquid (analyte). Additionally, the central core is coated by a gold layer to facilitate the coupling among the plasmonic modes and the core fundamental modes. A full vectorial finite element method is used to analyze the proposed sensor with a perfectly matched layer boundary condition. Further, the particle swarm optimization (PSO) technique is used to optimize and improve the sensitivity of the presented sensor as well as reduce the sensor’s size. Through the optimization process, the diameters of the three cores, and the thicknesses of the gold layer are fluctuated. For a wavelength range 1.46-1.47, the sensitivity of the proposed sensor is 4000 nm/RIU.

Design considerations of super-directive nanoantennas for core-shell nanowires

The metallodielectric Yagi antenna showed high directivity in the visible range as compared with all dielectric nanoantennas. In this paper, two different configurations have been introduced and analyzed: slanted nanowire optical Yagi antenna and asymmetric core-shell nanoantenna. Both designs have an Ag core and Si shell. The numerical results are obtained using the 3D FDTD technique. The proposed nanoantennas show ultradirective radiation in the direction of propagation. It has been shown that, by varying the angle Θ of the slanted nanowire directors, the directivity of the nanoantenna is enhanced, and the beam width becomes narrow in the desired direction. The directivity is improved to 21.23 when Θ=18°, and the radiation efficiency is enhanced to 54% at a wavelength of 500xa0nm. Additionally, the asymmetric core-shell Yagi design enhanced the directivity to 22.4 at a wavelength of 500xa0nm, with an enhancement of 30% over the symmetric design. This improvement is attributed to the near-field intensity enhancement of the asymmetric core-shell design. The variation of the silver core position may be beneficial for various applications, including surface-enhanced Raman spectroscopy, energy harvesting, photodetection, and photovoltaics.