Ultra-broadband spatial light modulation with dual-resonance coupled epsilon-near-zero materials

It has been found that the dielectric constants of transparent conductive oxides (TCOs) can be adjusted in an extremely large range by tuning the carrier density. Due to the remarkable light confinement property of the epsilon-near-zero (ENZ) effect of TCOs, it has attracted extensive interests of light modulation. However, the operation wavelength bandwidth is usually limited by optical resonance that is applied to enhance the light-TCOs interaction. In this work, a dual-resonance light coupling scheme is proposed to expand the modulation depth-bandwidth product with almost one order-of-magnitude improvement. In a metallic subwavelength grating structure with deep trenches backed by a ground plane, the ENZ mode can be coupled to both magnetic resonance and Fabry-Perot resonance respectively by tuning the bias. Decent light modulation can be obtained in a large operation wavelength band covering two resonances by optimizing the dual-resonance configuration. Such a reconfigurable efficient broadband modulation is important for robust communication link and possesses remarkable capacity for wavelength division multiplexing.