Electrically tunable active metasurfaces are attracting great interest as a possible means to realize two-dimensional pixelated surface-normal modulators for wide applications, such as high-speed imaging, optical interconnects, and photonic switching. In this work, we fabricate a metallic metasurface embedded with an electro-optic (EO) polymer and experimentally demonstrate the electrical tuning of its reflectance property. Unlike the previously demonstrated surface-normal modulators based on the EO polymer, we utilize the Fabry-Perot resonance of a metal-insulator-metal mode to trap the incident light inside a thin EO polymer layer to enhance the modulation efficiency. By applying voltage between the top and bottom layers of Au, we observe a clear spectral shift in the plasmonic resonance as well as a 5-MHz dynamic modulation at 1630-nm wavelength.

Electrically tunable metasurfaces have gained special interest as they can realize ultrathin surface-normal modulators in planar geometries. In this paper, we demonstrate a novel metasurface modulator based on electro-optic (EO) polymer that utilizes bimodal resonance inside a metallic subwavelength grating to increase the modulation efficiency. When two metal-insulator-metal (MIM) resonant modes are excited simultaneously inside the grating, they couple strongly to generate a sharp dip in the reflected spectrum. As a result, efficient intensity modulation with 15-dB extinction ratio can be obtained at the resonant wavelength under a small refractive index change of 8.5 × 10, corresponding to modulation voltage of less than 10 V. Due to the low parasitic capacitance of EO polymer and high conductivity of metallic gratings which is also used as the electrodes, the RC bandwidth of the device should easily exceed 100 GHz, potentially applicable to high-speed surface-normal modulators.

Abstract:We propose novel silicon-based surface-normal optical modulator using electro-optic (EO) polymer. The EO polymer is embedded inside a thin silicon subwavelength grating layer, which is used as both the interdigitated electrodes for effective poling of the EO polymer, and as high-Q resonant structure for the incident light to enable efficient modulation. We numerically demonstrate 10-dB intensity modulation at 1550-nm wavelength under a refractive index change of only 3.8 × 10 −4 , corresponding to the driving voltage below 1 V. Total-reflectance phase modulator is also demonstrated by adding a backside reflector. With inherently high-speed response over several tens of GHz, scalability to dense 2-D array integrated with CMOS driver circuitry, and relatively easy and low-cost fabrication without epitaxial process, the proposed device may find versatile applications in optical interconnects, free-space optical communications, imaging and sensing.

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