A novel proposal for all optical 2 × 4 decoder based on photonic crystal and threshold switching method

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.

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

In this paper, a compact graphene-based plasmonic D flip-flop is presented where the graphene waveguides are sandwiched between two SnO2 layers. The structure includes two input ports CLK and D, and two output ports Q and Q'. The input signals transmit through the waveguides and interfere with other signals. A portion of input signal D appears at port Q, and another portion interferes with the incoming signal from port CLK then is guided toward port Q'. The commercial Lumerical software is used to solve Maxwell’s equations and simulate the propagation of terahertz waves. The finite difference time domain method is used to calculate the electric and magnetic components of waves throughout the structure. The structure is studied at the transverse magnetic mode, and the perfectly matched layer is assumed at boundaries. The wavelength is assumed from 12.7 µm to 13.1 µm, and the area of the structure is 0.83 µm2. The small area of the designed flip-flop is an essential feature for use in optical integrated circuits. The contrast ratio of outputs Q and Q' is about 7.3 dB and 13 dB, respectively which is more than the previous work. In comparison to the last work which had one port for signal Q, two output ports for signals Q and Q' are designed in this work. This feature is needed for employing the flip-flop at sequential circuits. 

Design and simulation of a compact graphene-based plasmonic D flip-flop

In this work, an optimized structure for an all-optical XOR gate with high contrast ratio and extremely compact dimension is proposed based on a photonic crystal platform. The above structure employs silicon rods in a hexagonal lattice configuration. The design works purely on linear interference effect between the incoming light signals without utilizing any non-linear materials. To study the propagation of light within the structure and to generate the bandgap diagram, the Finite Difference Time Domain technique and Plane Wave Expansion methods are utilized. After optimization of the various design parameters, a contrast ratio of 31.76 dB is attained by the proposed structure along with a response time of 0.46 ps and a footprint of 42.24 μm2. The device can be operated in the C Band with optimum performance at 1550 nm, which is the telecommunication wavelength. The operating bit rate for the proposed structure is 2.17 Tbps. The all-optical XOR gate plays a crucial role as the building blocks of various sequential and combinational logic designs suitable for application in optical computing and telecommunication systems. 

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T Shankar

Papers

All optical clocked D flip flop for 1.72 Tb/s optical computing