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

An alternative approach of developing a frequency encoded data based asynchronous Counter in C-Band

In this paper all optical ultra compact 4:2 encoder is proposed and designed using two dimensional photonic crystals (PC). The proposed structure has silicon rods of refractive index 3.4 embedded in air host by creating line defects in hexagonal lattice platform. The analysis of the design is done for various experimental values of radius, lattice constant and pitch values using finite difference time domain (FDTD) and plane wave expansion (PWE) method of licensed OptiFDTD software tool. The structure is optimised to get maximum power confinement at the output of the two ports of the 4:2 encoder by inserting extra rods which interns acts like a resonator to couple the power to the two output waveguides. The structure is chosen in such a way that ( $$\frac{a}{\lambda }$$ ) will fall around 1550 nm wavelength only and is good for long distance transmission application as it is having low attenuation constant and high contrast ratio. Further, the proposed 4:2 encoder is operated at 1550 nm and it provides a high contrast ratio of 9.25 dB, propagation delay 33.1 fs and foot print of the structure is 119.34 $$\mu$$ m $$^2$$ . Hence it is highly advisable for photonic integrated circuits and optical signal processing. 

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Design of ultra compact 4:2 encoder using two dimensional photonic crystals

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The presented research deals with designing of a new ultra compact all-optical RS flip-flop on a two-dimensional (2-D) hexagonal photonic crystal platform. The flip-flop is designed by using two NOR gates, photonic crystal waveguides, four silicon ring resonators, four input ports and two output ports. The designed flip-flop structure has hexagonal silicon rods in the air host with a lattice constant a of 630 nm. Si rods have a radius of 0.2a and operating waveleangth of 1550 nm. The novel design provides proper distinction between logic 1 and logic 0 at the output by giving 8.7 dB and 4 dB contrast ratio at Q and Qbar output, respectively. Furthermore, uncomplicated structure resulting in small dimension of 28 μm * 28 μm makes it appropriate for optical integrated circuit in optical networks. FDTD method is used to model the proposed structure and simulated using RSoft FullWAVE simulator tool.

Mahesh V. Sonth

Papers

Design of two-dimensional photonic crystal based ultra compact optical RS flip-flop