Designing OR logic gate using two-dimensional optical crystal according to Mach Zehnder filter suitable for all-optical digital integrated circuits

Author Name: Rahim Valinia
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Abstract

Photonic crystals can be simply defined as an environment with intermittent optical properties which consist of intermittent dielectric and has one-, two- and three-dimensional structures. One of the unique properties of optical crystals is the property of controlling the light passing through the area called photonic band gap which is due to the intermittence of dielectric in optical crystals. Photonic crystal is highly dispersive and its permittivity and reflection are heavily dependent on the wavelength. In this study, OR all-optical logic gates were designed, analyzed and simulated. The basis of the gates is light (electromagnetic waves). These gates were designed as silicon rods in the air by two-dimensional optical crystals with different networks. The basis of the gates are defect and interference of light waves. Controlling the light was done within the gate using the defect. Using interference effect which can be constructive or destructive, the output of logical zero or one was obtained. The advantages of these gates compared to similar electronic gates are lower dissipation, higher speed (at the speed of light), simpler structure, zero power consumption in a relaxed state and etc. which are investigated later. To simulate these gates, two methods of finite difference in the time domain and the expansion of plane waves were used. The first one was used to calculate the electric field distribution and the second one was used to calculate the photonic band. The results of simulation using Rsoft software contains graphic charts.

Keywords

photonic crystal, band gap, OR optical gate

Introduction

Although the studies on photonic crystals were started since 1887 but no one used the term photonic crystal until over 100 years later—after Eli Yablonovitch and Sajeev John published two milestone papers on photonic crystals in 1987. Applications of photonic crystals have been expanding rapidly during the past decades. Some of the latest and greatest were highlighted here. Probably, theirs most interesting and most important application was the use of them in fiber-optic communications. The unique feature of photonic crystals, i.e. reflecting the light completely when its frequency is within the photonic band gap, increases dramatically the possibility of reducing casualties in the fiber sheath. Also, it is no need that the light spread in the dielectric. The light can be actually guided in a vacuum or air with low pressure which then, nonlinear effects and fiber losses become very low.

1-1- Optical crystal

Any structure that its refractive index intermittently changes, is called optical crystals. If this is repeated in one dimension, the formed crystals are called one-dimensional optical crystals. Repeating the intermittent structure in two or three dimensions will create two- and three- dimensional optical crystals. These structures are in fact dual semiconductor crystals. So, the performance of optical crystals (structures with intermittent refractive index) against photons is similar to the performance of semiconductor crystals (structures with intermittent electric potential) against electrons.

1-2- Optical crystal structure

Photonic crystals can be simply defined as an environment with intermittent optical properties. For example, an intermittent optical environment is shown in figure (1-2) that the dark parts have homogeneous and different electric permittivity e and magnetic permittivity m compared to light parts. This system can be considered as a simple one-dimensional photonic crystal. Photonic crystal is highly dispersive and its permittivity and reflection are heavily dependent on the wavelength. In the following figure, this property is shown for a photonic crystal that its permittivity coefficient is greater than zero for blue light and almost zero for red light.

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