Nanophotonic Ultrashort Coupler Based on Hybrid Plasmonic Waveguide With Lateral Subwavelength Grating

A nanophotonic vertical coupler with ultrashort coupling length based on hybrid plasmonic (HP) waveguide with a lateral subwavelength grating (LSG) is proposed. An ultrashort coupling length of 0.461 μm is achieved through the lateral resonances in the subwavelength grating. The combined effect of LSG and the metal layer sandwiched between the coupling dielectric-regions makes it possible to realize efficient coupling and low-loss guiding of hybrid modes with a propagation lengths of 123 and 53 μm, respectively, for odd and even modes. The vertical coupling influenced by the lateral resonances through LSG also exhibits broadband nature where the coupling length remains acceptably small and the coupling performance remains high over a broad range of wavelengths. The coupling performance of 192 and a low propagation loss of 0.035 dB/μm are reported with the analysis based on finite element method. LSG introduced into the HP waveguide is shown to provide multifold benefits of increased fabrication tolerance, enhanced coupling efficiency and expanded coupling regime.