Simultaneous Optical Half-Adder and Half-Subtracter Using a Single-Slot Waveguide

We propose a simple approach for simultaneous optical half-adder and half-subtracter using a single-slot waveguide that offers tight light confinement and enhanced nonlinearity. By exploiting the parametric depletion effect of twin degenerate four-wave mixing processes in the slot waveguide, we simulate 160-Gbit/s half-adder (A + B) and half-subtracter (A - B, B - A) and characterize the operation performance in terms of quality Q factor, extinction ratio ER, and eye opening EO. Two different nonlinear materials are considered as the slot region for comparison. One is silicon-nanocrystal (Si-nc) with Kerr nonlinear index of refraction (n2) of 4.8 ×10^-17 m²/W and two-photon absorption (TPA) coefficient (βTPA) of 7 ×10^-11 m/W at 1550 nm, and the other is a specific polydiacetylene, poly-[2,4 hexadiyne -1,6 diol-bis-( p -toluene sulfonate)] (PTS) with n2 = 6.25 ×10^-17 m²/W and βTPA ≈ 0 at 1550 nm. PTS slot waveguide features superior performance of half-adder and half-subtracter compared with Si-nc slot waveguide under the same waveguide length and input signal power. Moreover, we study the performance dependence on the waveguide length and input power, providing an easy-to-follow theoretical basis for achieving the desired performance of half-adder and half-subtracter.