In this paper, a new photonic crystal-based structure has been proposed for the all-optical 2-to-4 decoder. The structure consists of an array of 19 × 15 chalcogenide rods in the form of the square lattice with a lattice constant of 517 nm. A bias and two input signals are guided through the three waveguides toward the cross-connections to have the constructive interferences. The obtained signal is transmitted through a waveguide that is connected to three nonlinear cavities. To approach the optical Kerr effect, one rod made of a doped-glass with a nonlinear coefficient of 10 −14 m 2 W −1 is placed in each cavity. Based on the amount of the optical intensity, the waves are dropped and guided toward the desired output ports. To obtain the dropping operation at different intensities, the radii of nonlinear rods are adjusted to be 1.13, 1.07, and 1.01 times of ones for the fundamental rods. Unlike the previous works, there is no resonant ring in the proposed structure so the footprint of the device has been reduced to 76 µm 2 compared to other works. Furthermore, the delay time of the proposed structure is approximately equal to 210 fs which is less than one for all previous works. Besides, the contrast ratio of output ports has been obtained 13.52 dB that is higher than one for other structures. The fast response, small size, and the high contrast ratio of the presented device demonstrate that an improvement in the performance of the photonic crystal-based decoder has been obtained in this work.

In this paper, a photonic crystal structure based on nonlinear cavities has been proposed to improve the time response of a 2-to-4 decoder. The structure includes an array of chalcogenide rods with an air gap in which the spatial period of rods is 500 nm. The radius of the fundamental rods is assumed to be 125 nm, which results in a photonic bandgap of 1092–1724 nm at TM mode. Three cavities, including the nonlinear rods with a Kerr coefficient of 10 − 14 m 2 / W , drop the incoming waves concerning the amount of optical intensity. The finite-difference time-domain method was used to calculate the components of the electric and magnetic fields throughout the structure. The time analysis of the device shows the rise time is equal to 200 fs, which is less than one for the previous structures. The area of 110 µ m 2 and the margins of 4% and 88% for logics 0 and 1 are other advantages of the proposed structure. Based on the obtained results, it was proven that the performance of the 2-to-4 photonic crystal-based decoder has been improved by this work.

In this study, a novel, two-dimensional photonic crystal-based structure for the 2-to-4 optical decoder is presented. The structure consists of 23 rows and 14 columns of chalcogenide rods that are arranged in a square lattice with a spatial periodicity of 530 nm. The bias and the optical signals are guided toward the main waveguide through the three waveguides. Two unequal powers are applied to the input ports to approach the different intensities proportional to four working states into the main waveguide. Four cavities including the nonlinear rods are in response to drop the optical waves toward the output ports. To calculate the band diagram and the spatial distribution of the electric and magnetic fields, the plane wave expansion and the finite difference time domain methods have been used. The delay time of the designed structure is obtained around 220 fs, which is less than one for the previous structures. Furthermore, the gap between the margins for logic 0 and 1 is equal to 83%, which is higher than one for other works. Besides, the area of the structure is reduced to 90 µm2 in comparison to all reported structures. Based on the mentioned results, it seems that an improvement of the performance for 2-to-4 optical decoders has been obtained in this research.

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