Plasmonic technology has attracted intense research interest enhancing the functional portfolio of photonic integrated circuits (PICs) by providing Surface-Plasmon-Polariton (SPP) modes with ultra-high confinement at sub-wavelength scale dimensions and as such increased light matter interaction. However, in most cases plasmonic waveguides rely mainly on noble metals and exhibit high optical losses, impeding their employment in CMOS processes and their practical deployment in highly useful PICs. Hence, merging CMOS compatible plasmonic waveguides with low-loss photonics by judiciously interfacing these two waveguide platforms appears as the most promising route towards the rapid and costefficient manufacturing of high-performance plasmo-photonic integrated circuits. In this work, we present butt-coupled plasmo-photonic interfaces between CMOS compatible 7μm-wide Aluminum (Al) and Copper (Cu) metal stripes and 360×800nm Si3N4 waveguides. The interfaces have been designed by means of 3D FDTD and have been optimized for aqueous environment targeting their future employment in biosensing interferometric arrangements, with the photonic waveguides being cladded with 660nm of Low Temperature Oxide (LTO) and the plasmonic stripes being recessed in a cavity formed between the photonic waveguides. The geometrical parameters of the interface will be presented based on detailed simulation results, using experimentally verified plasmonic properties for the employed CMOS metals. Numerical simulations dictated a coupling efficiency of 53% and 68% at 1.55μm wavelength for Al and Cu, respectively, with the plasmonic propagation length Lspp equaling 66μm for Al and 75μm for Cu with water considered as the top cladding. The proposed interface configuration is currently being fabricated for experimental verification.
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.