Nihal F. F. Areed

Fully Integrated AND and OR Optical Logic Gates

We propose two novel designs of compact, linear, and all-optical OR and AND logic gates based on photonic crystal architecture. The proposed devices are formed by the combination of the ring cavities and Y-shape line defect coupler placed between two waveguides. The performance of the proposed logic gates has been analyzed and investigated using finite difference time domain method. The suggested design for AND gate offers ON to OFF logic level contrast ratio of not less than 6 dB and the suggested design for OR gate offers transmitted power of not less than 0.5. On top of that, the proposed OR and AND logic gates can operate at bit rates of around 0.5 and 0.208 Tb/s, respectively. Further, the calculated fabrication tolerances of the suggested devices show that the rods radii of the ring cavities need to be controlled with no more than ±10% and ±3% fabrication errors for optical OR and AND gates, respectively. It is expected that such designs have the potential to be key components for future photonic integrated circuits due to their simplicity and small size.

Proposal of an Ultracompact CMOS-Compatible TE-/TM-Pass Polarizer Based on SoI Platform

An all-dielectric transverse electric (TE)-/transverse magnetic (TM)-pass polarizer based on silicon-on-insulator (SoI) is proposed and analyzed. The symmetric etching of the silicon nanowire with specific values allows the cutoff of the undesired polarization state while the other is propagated with minimal losses. The proposed SoI polarizer can achieve 26- and 30-dB extinction ratios and 0.4-dB insertion losses for both TE- and TM-pass polarizers, respectively, with a very compact device length as short as 2.5 μm. The polarizer maintains <;1-dB insertion loss and >20-dB extinction ratio over a wide wavelength range of 1.454-1.68 μm. Fabrication of the introduced device is compatible with standard CMOS fabrication process.

Ultra-high efficient solar cell based on decagonal arrays of silicon nanowires

Abstract. Silicon nanowires (SiNWs) are the subject of intense research in solar energy harvesting due to their unique electrical and optical characteristics. The transmission, reflection, and absorption spectra of decagonal Si NWs (D-SiNWs) solar cells have been calculated using a three-dimensional finite-difference time-domain method to present a design guideline for ultra-high efficiency SiNW in solar cell applications. In this study, the structure geometrical parameters of the suggested design are tuned to maximize light absorption. The ultimate efficiency is used to quantify the absorption enhancement of the SiNWs solar cells. A maximum ultimate efficiency of 39.3% is achieved for the reported D-SiNWs, which is greater than that of the previous work of slanting Si NWs by 17.49%.

Novel All-Optical Liquid Photonic Crystal Router

A novel design of an easily and fully integrated terabit per second (Tbit/s) optical router is presented and analyzed using the finite difference time domain method. The proposed router consists of three photonic bandgap (PBG) waveguides with two nematic liquid crystal (NLC) layers. The suggested device can be used to divert the light beam to one of the three photonic crystal waveguides based on the biasing states of the two NLC layers. In this way, there are three different modes of operation where each one is used for routing data to the required direction. The suggested device offers crosstalk of 19 dB. In addition, the reported structure opens up the revenue for building multi-port optical routers through the use of a number of appropriately positioned NLC layers within the platform of PBG structure.

Multiple Image Encryption System Based on Nematic Liquid Photonic Crystal Layers

A novel design for multiple symmetric image encryption system based on a phase encoding is presented. The proposed encryptor utilizes a photonic bandgap (PBG) block in order to ensure high reflectivity over a relatively wide frequency range of interest. Also, the proposed encryptor can be utilized to encrypt two images simultaneously through the use of two nematic liquid crystal (NLC) layers across the PBG block. The whole system has been simulated numerically using the rigorous finite difference time domain method. To describe the robustness of the encryption, a root mean square of error and the signal to noise ratio are calculated. The statistical analysis of the retrieved images shows that the proposed image encryption system provides an efficient and secure way for real time image encryption and transmission. In addition, as the proposed system offers a number of advantages over existing systems such as simple design, symmetry allowing integrated encryptor/decryptor system, ultra high bandwidth and encrypting two images at the same time, it can be suitably exploited in optical imaging system applications.

Funnel-shaped silicon nanowire for highly efficient light trapping.

In this Letter, funnel-shaped silicon nanowires (SiNWs) are newly introduced for highly efficient light trapping. The proposed designs of nanowires are inspired by the funnel shape, which enhances the light trapping with reduced reflections in the wavelength range from 300 to 1100 nm. Composed of both cylindrical and conical units, the funnel nanowires increase the number of leaky mode resonances, yielding an absorption enhancement relative to a uniform nanowire array. The optical properties of the suggested nanowires have been numerically investigated using the 3D finite difference time domain (FDTD) method and compared to cylindrical and conical counterparts. The structural geometrical parameters are studied to maximize the ultimate efficiency and hence the short-circuit current. Carefully engineered structure geometry is shown to yield improved light absorption useful for solar cell applications. The proposed funnel-shaped SiNWs offer an ultimate efficiency of 41.8%, with an enhancement of 54.8% relative to conventional cylindrical SiNWs. Additionally, short-circuit current of 34.2  mA/cm2 is achieved using the suggested design.

Novel Plasmonic Data Storage Based on Nematic Liquid Crystal Layers

In this paper, compact plasmonic data storage with high-speed sequential writing/reading rate has been proposed and numerically simulated using two-dimensional finite difference time domain method. The proposed storage is composed of a combination of two nematic liquid crystal (NLC) layers and nano-silver sheet perforated with two rectangular nano-holes. The suggested storage has been designed for storing visible light in one of the two nano-holes based on the biasing states of NLC layers. Tuning the dimensions of the proposed storage results in storing three different binary states “01,” “10,” and “11” with 0.4 power absorption efficiency, 13 dB crosstalk and 1 Gbps sequential writing/reading rate. It is expected that such proposed two-bit binary storage can be used as a basic unit for constructing large scale storage device with high storage capacity and ultra-high bit rate.

Hybrid core semiconductor nanowires for solar cell applications

In this study, novel design of semiconductor nano-wires in decagonal lattice with hybrid core is proposed and simulated using 3D finite difference time domain method. The hybrid core has gold/silicon combination to increase the light absorption and hence the ultimate efficiency. The reported NWs solar cell achieves broadband absorption in long wavelength region with excellent absorption (>95%) in short wavelength regime. The proposed structure with hybrid core shows an ultimate efficiency of 32.62 % which is higher than that of silicon core design by 19.7%.

NOVEL DESIGN OF SYMMETRIC PHOTONIC BANDGAP BASED IMAGE ENCRYPTION SYSTEM

A novel approach for the design of image encryption system based on one stage of 3D photonic bandgap structure is proposed. Using the Finite Integration Time Domain (FITD) method, the performance of the proposed design is optimized through the utilization of the re∞ection properties from 3D photonic bandgap structure while maintaining constant phase encoding. To demonstrate the robustness of the suggested encryption system, root mean square error is calculated between the original and decrypted images revealing the high accuracy in retrieving the images. In addition, as the proposed system renders itself as easy to fabricate, it has an excellent potential for being very useful in both microwaves and photonics imaging system applications.

Broadband Omnidirectional Nearly Perfect Plasmonic Absorber For Solar Energy Harvesting

In this paper, an efficient, broadband, omnidirectional visible plasmonic absorber is presented and numerically simulated using the rigorous three-dimensional finite difference time domain (FDTD) method and the 2-D finite element method. The proposed absorber comprises hollow cylindrical layers of aluminum (Al) and silicon dioxide (SiO2). Arranging the geometry and adjusting the dimensions of the cylindrical layers generate localized plasmonic modes at the Al/SiO2 interfaces, as well as inside the gap between two Al layers, and thereby, strong optical confinement in the visible range is allowed. Therefore, the light absorbance of over 93% is observed over the whole visible regime with a relative bandwidth from 0.4 to 0.75 PHz. Further, due to the cylindrical geometry, the absorption is almost independent on the incident angles in a wide range (-90° to 90°). Two elements of the proposed absorber have been employed to function as a nanoantenna for converting the solar energy to electricity. The proposed nanoantenna offers omnidirectional harvesting characteristics with efficient harvesting efficiency that is higher than that of the conventional rectangular dipole nanoantenna by about 38%.