All-optical switching at the Fano resonances in subwavelength gratings with very narrow slits.

We theoretically discuss all-optical switching at the Fano resonances of subwavelength gratings made of a chalcogenide glass (As(2)S(3)). Particular attention is devoted to the case in which the grating possesses extremely narrow slits (channels ranging from a∼10 nm to a∼40 nm). The remarkable local field enhancement available in these situations conspires to yield low-threshold switching intensities (~50 MW/cm(2)) at telecommunication wavelengths for extremely thin (d∼200 nm) gratings when a realistic value of the As(2)S(3) cubic nonlinearity is used.