Elsevier

Optik

Volume 125, Issue 19, October 2014, Pages 5701-5704
Optik

All optical NOR and NAND gate based on nonlinear photonic crystal ring resonators

https://doi.org/10.1016/j.ijleo.2014.06.013Get rights and content

Abstract

In this paper we proposed optical NOR and NAND gates. By combining nonlinear Kerr effect with photonic crystal ring resonators first we designed a structure, whose optical behavior can be controlled via input power intensity. The switching power threshold obtained for this structure equal to 2 kW/μm2. For designing the proposed optical logic gates we employed two resonant rings with the same structures, both rings at the logic gates were designed such that their resonant wavelength be at λ = 1550 nm. Every proposed logic gate has one bias and two logic input ports. We used plane wave expansion and finite difference time domain methods for analyzing the proposed structures.

Introduction

The advent of photonic crystals (PhCs) [1] had revolutionized the optical and photonic device designing field. PhCs are periodic structures, mostly composed of 2 different materials with high and low refractive indices [2]. According to the refractive index distribution function of these structures, they are divided into 3 categories: one, two and three dimensional PhCs. The periodic nature of PhCs gives them the ability to prohibit the propagation of optical waves in certain frequency ranges called photonic band gap (PBG). Due to this PBG property PhCs can confine and guide optical waves inside ultra-small spaces and waveguides. 2D PhCs due to their complete PBG and ease of design and fabrication attract more attention than 1D and 3D structures do. Obtaining suitable PBG region is very important in designing optical PhC-based devices. PBG region in 2D PhCs depends on the refractive index of the dielectric materials, the shape of the rods, the crystal structure, and the radius of the rods and the lattice constant of the structure [3], [4], [5].

All optical logic gates play a crucial role in all optical signal processing and optical communication networks. Low loss transmission, immunity to electromagnetic interference, high bandwidth and high data transmission and processing speed are the main advantages of optical networks. Optical devices such as optical filters, demultiplexers, switches and logic gates are the fundamental structures for realizing all optical networks, which can work completely in optical domain without employing electronics. One mechanism proposed for designing optical gates is based on waveguide interferometers [6], but due to their dimensions they are not suitable for integrated optical circuits [7]. Semiconductor optical amplifiers (SOAs) [8] are another mechanism used for creating optical logic gates, whose performance is limited by spontaneous emission noise and complexity of integration [9], [10]. PhC ring resonators (PhCRRs) are basic structures used for designing opticl devices such as optical filters [11], [12], [13], [14], optical demultiplexers [15], [16], [17], and optical switches [18]. A PhCRR simply is an optical device composed of a resonant ring sandwiched between two parallel waveguides called bus and drop waveguides. At a certain wavelength – resonant wavelength – optical waves in bus waveguide will drop to drop waveguide through the resonant ring. So PhCRR structure can perform filtering behavior. It has been shown that the resonant wavelength of PhCRRs depends on the refractive index and structural parameters of the ring core structure [19]. This property has been used for designing optical demultiplexers, by employing multiple resonant rings with different structural parameters in a single structure [20]. As far as we know high power optical waves trigger nonlinear effect in dielectric materials, which is called kerr effect [21]. It means that at high powers, the refractive index of dielectric materials depends on the power intensity of incident light. So we can control the optical behavior of the PhCRR structure via input intensity, and realize switching task.

Different kinds of optical logic gates have been proposed based on PhCs recently. An optical AND gate has been designed using nonlinear ring resonators by andalib and Granpaye [22]. Bai et al. [23] proposed optical NOT and optical NOR gates based on PhCRRS. Another optical NOR gate based on PhCRRs has been proposed by Isfahani et al. [24]. Danaie and Kaatuzian [25] proposed an optical AND gate based on PhC structures. In this paper we used nonlinear PhCRRs for designing two optical logic gates. An optical NOR and an optical NAND gate are proposed in this paper. To the best of or knowledge our structure is the first optical NAND gate proposed based on photonic crystals. We used plane wave expansion [26] and finite difference time domain [27] methods for analyzing the proposed structures.

The rest of the paper has been organized as follows: in Section 2 we proposed the basic nonlinear PhCRR structure then in Section 3 we discussed the design and results of the NAND and NOR gates. Finally in Section 4 we conclude from our work.

Section snippets

PhC ring resonator

As we mentioned the basic structure used for designing the optical logic gates in this paper is a photonic crystal ring resonator. The photonic crystal structure used for designing the PhCRR is a 31 × 21 square array of chalcogenid glass rods with refractive index of 3.1 in air. The radius of the rods is r = 0.215 × a, where a = 630 nm is the lattice constant of the structure. For this structure the band structure diagram has been calculated and obtained like Fig. 1. This PhC structure has BPG region at

NOR gate

The proposed structure for optical logic NOR gate is shown in Fig. 4. It consists of two nonlinear resonant rings and five waveguides. Our structure has four ports. The logic ports are shown via A and B letters. Each logic port is connected to the corresponding resonant ring with a one waveguide. The resonant rings have been designed such that their resonant wavelength at input intensities lower than the switching threshold – 2 kW/μm2 – to be at λ = 1550 nm. The bias pulse enters the structure

Conclusion

In this paper we first we proposed a PhCRR structure, whose optical behavior was controllable via intensity of input power. The PhCRR was designed such that its resonant wavelength at power intensities lower than the switching threshold – 2 kW/μm2 – to be at λ = 1550 nm. The resonant wavelength of the proposed structure depends on the refractive index of ring core rods, so by increasing the intensity of input power due to the nonlinear Kerr coefficient the refractive index of the structure will

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