Optical Half Adder Based on Linear Optical Interference Using a Multimode Interference Structure

Abstract

With the rapid growth of artificial intelligence, photonic computing has attracted increasing attention as an energy-efficient alternative to electronic computing. Optical half adders have been realized using semiconductor optical amplifiers (SOAs), plasmonic waveguides, photonic crystals (PhCs) and inverse-designed photonic structures. However, many existing approaches rely on nonlinear effects, metallic absorption, limited complementary metal oxide semiconductor (CMOS) compatibility or computationally intensive optimization. In this paper, a two-bit optical half adder based on passive linear optical interference is proposed. The device consists of a four-input, three-output silicon-on-insulator (SOI) waveguide circuit employing multimode interference structures and Y-branch waveguides. It operates with two binary phase-shift keying (BPSK) input signals and a single probe light, simultaneously performing XOR and AND logic operations. The device was analytically designed, fabricated on an SOI platform and experimentally demonstrated. Measured extinction ratios of 6.8 and 5.5 dB were obtained for the XOR and AND outputs, respectively. The proposed MMI-based device offers low power consumption, low insertion loss, low design complexity and CMOS compatibility, making it a promising building block for future photonic computing systems.