Unidirectional data center interconnects enabled by the use of Broken-Symmetry Gap Plasmon Resonators (BS-GPR)

Grating couplers are the most versatile mechanism to couple light efficiently into photonic interconnects, such as waveguides featuring submicronic cross-sections. Usually grating couplers are used in a tilted illumination configuration in order to obtain unidirectional excitation of the waveguide, requiring challenges in assembly and packaging. In practical applications, tilted illumination of the gratings is not always possible in particular for fully integrated electrooptical printed circuit board (EO-PCB) with a light source (Vertical-Cavity Surface-Emitting Laser (VCSEL)) and an optical layer implanted on each side of the board. In this case, the incoming light hits the gratings couplers at normal incidence and specific strategies are needed to achieve unidirectional excitation of the guided mode. In this work, a novel unidirectional Data Center coupling concept based on the use of gap plasmon polariton (GPR) grating couplers sustained by Metal-Insulator-Metal (MIM) resonators is introduced. Unlike traditional challenging subwavelength coupling schemes based on plasmonics and Si-Photonics, we consider non-symmetric GPR featuring highly directional scattering efficiency. The plasmonic gratings have been modelled numerically employing a Fourier Modal Method and the results have been confirmed by FEM simulations.