Investigations on All-Optical Binary to Gray and Gray to Binary Code Converters Using 2D Photonic Crystals

This work investigates a novel design to realize 3-bit binary to gray code and gray to binary code converter utilizing all-optical XOR gates on a photonic crystal platform. An ultra-compact and high contrast ratio XOR gate working at 1550 nm is implemented using silicon rods on a hexagonal lattice with air substrate. The operation principle is the linear interference effect which leads to power efficient operation. The proposed designs are aimed at reducing the dimensions and enabling flexible and compatible operation with an Optical Integrated Circuit. The designs are optimized with respect to structural parameters such as lattice constant and radius to achieve the maximum contrast ratio and minimum response time. The proposed structures exhibit compact footprints of
$100.04~\mu \text{m}^{2}$
and
$105.6~\mu \text{m}^{2}$
for the all-optical gray to binary code converter and binary to gray code converter respectively. The corresponding values of contrast ratio are attained as 11.24 dB and 13.46 dB respectively. To analyse the structures and to calculate the required performance metrics, the Finite Difference Time Domain Method is used. This is the first time that a design for an all-optical gray to binary code converter has been attempted on a photonic crystal platform. The proposed design is successfully implemented with cascaded layout using interference effect without employing any additional phase control mechanisms. Gray codes are widely employed in optical communication systems for several applications such as improved switching, error correction and encryption. All-optical code converters form crucial elements in all-optical computing to enable efficient code conversions for high-speed photonic integrated circuits.