Adiabatic mode transformation in width-graded nano-gratings enabling multiwavelength light localization

Abstract We delineate the four principal surface plasmon polariton coupling and interaction mechanisms in subwavelength gratings, demonstrate their significant roles shaping optical response of plasmonic gratings. Within framework width-graded metal–insulator-metal nano-gratings, electromagnetic field confinement wave guiding result multiwavelength light localization provided conditions adiabatic mode transformation are satisfied. The is enhanced further through fine tuning groove-width ( w ), groove-depth L ) groove-to-groove-separation d ). By juxtaposing resonance modes non-graded gratings defining adiabaticity condition, we criticality achieving among grooves. observe that resonant wavelength a graded grating corresponds to properties single groove when grooves adiabatically coupled. show plays an important function span localized wavelengths. Specifically, with intensity enhancement exceeding three orders magnitude possible < 30 nm 300 900 for range fixed values . This study presents novel paradigm deep-subwavelength adiabatically-coupled gratings—illustrating its versatility design, hence viability applications ranging from Raman spectroscopy multispectral imaging.