Ultracompact, high-extinction ratio XOR, OR, and Feynman logic gates based on plasmonic metal–insulator–metal directional couplers
Sirous Tannaz, Mojtaba Moradkhani, Mahshid Taherzade, Mir Hamid Rezaei
Abstract
Three plasmonic logic gates including XOR, OR, and Feynman based on directional couplers operating in the optical communications band are proposed. First, a 3 dB directional coupler based on metal–insulator–metal waveguides is presented and its operation principles are investigated using the coupled mode theory method. Then, XOR and OR logic gates are implemented simultaneously in one structure. The simulations performed by the finite-difference time-domain method show that the extinction ratios for the OR and XOR gates are infinite and 29.3 dB, respectively. The Feynman gate is also implemented using two directional couplers placed parallel to each other. The ER values for outputs <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi>P</mml:mi> </mml:mrow> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi>Q</mml:mi> </mml:mrow> </mml:math> are 7.26 dB and 34.23 dB, respectively. The footprints of the XOR/OR and Feynman structures are less than <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mn>8</mml:mn> </mml:mrow> <mml:mspace width="thickmathspace"/> <mml:mtext>µ</mml:mtext> <mml:msup> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">m</mml:mi> </mml:mrow> <mml:mn>2</mml:mn> </mml:msup> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mn>12</mml:mn> </mml:mrow> <mml:mspace width="thickmathspace"/> <mml:mtext>µ</mml:mtext> <mml:msup> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">m</mml:mi> </mml:mrow> <mml:mn>2</mml:mn> </mml:msup> </mml:math> , respectively. The presented gates have a high potential to be used in photonic integrated circuits.