An efficient and ultra-broadband unidirectional optical coupler for wide incidence angles

We have proposed an efficient and broadband unidirectional optical coupler composed of a four-layer (dielectric-metallic gratings-dielectric-metal) structure for wide incidence angles. Based on joint effects of the plasmonic critical angle phenomenon (PCA), the zero-order grating resonance, and the first-order Fabry-Perot (FP) resonance of the metal-dielectric-metal (MDM) waveguide, the illuminated TM-polarized light could be efficiently coupled into MDM waveguides with angular-full-width-half-maximum (AFWHM) widen to 50°over a broad wavelength range 750–1000 nm.

An efficient and unidirectional optical coupling scheme for metal-dielectric-metal (MDM) waveguides with wide-angle and ultra-broadband efficiency is proposed and demonstrated. Based on joint effects of the plasmonic critical angle phenomenon (PCA), the zero-order grating resonance, and the first-order Fabry–Perot (FP) resonance of the MDM waveguide, the illuminated light could be efficiently coupled into MDM plasmonic waveguide with angular-full-width-half-maximum (AFWHM) widen to 50° over a broad wavelength range 750–1000 nm. The operation principle and performance of the structure are clarified and theoretically illustrated.