Efficient coupling between Si3N4 photonic and hybrid slot-based CMOS plasmonic waveguide

Bringing photonics and electronics into a common integration platform can unleash unprecedented performance capabilities in data communication and sensing applications. Plasmonics were proposed as the key technology that can merge ultra-fast photonics and low-dimension electronics due to their metallic nature and their unique ability to guide light at sub-wavelength scales. However, inherent high losses of plasmonics in conjunction with the use of CMOS incompatible metals like gold and silver which are broadly utilized in plasmonic applications impede their broad utilization in Photonic Integrated Circuits (PICs). To overcome those limitations and fully exploit the profound benefits of plasmonics, they have to be developed along two technology directives. 1) Selectively co-integrate nanoscale plasmonics with low-loss photonics and 2) replace noble metals with alternative CMOS-compatible counterparts accelerating volume manufacturing of plasmo-photonic ICs. In this context, a hybrid plasmo-photonic structure utilizing the CMOS-compatible metals Aluminum (Al) and Copper (Cu) is proposed to efficiently transfer light between a low-loss Si3N4 photonic waveguide and a hybrid plasmonic slot waveguide. Specifically, a Si3N4 strip waveguide (photonic part) is located below a metallic slot (plasmonic part) forming a hybrid structure. This configuration, if properly designed, can support modes that exhibit quasi even or odd symmetry allowing power exchange between the two parts. According to 3D FDTD simulations, the proposed directional coupling scheme can achieve coupling efficiencies at 1550nm up to 60% and 74% in the case of Al and Cu respectively within a coupling length of just several microns.