Metamaterial electro-optic switch of nanoscale thickness

Abstract

We demonstrate an innovative concept for nanoscale electro-optic switching. It exploits the frequency shift of a narrow-band Fano resonance mode in a plasmonic planar metamaterial induced by a change in the dielectric properties of an adjacent chalcogenide glass layer. An electrically stimulated transition between amorphous and crystalline forms of the glass brings about a 150 nm shift in the near-infrared resonance providing transmission modulation with a contrast ratio of 4:1 in a device of subwavelength thickness. © 2010 American Institute of Physics. ͓doi:10.1063/1.3355544͔ Nanophotonic applications, in particular, photonic data processing circuits, require active devices of subwavelength dimensions. However, electro-optic modulation of light in a device of nanoscale thickness is not a trivial problem. In conventional modulators exploiting the Pockels or Kerr effects, the polarization switching involved requires the interference of two propagating modes to develop over distances far in excess of the wavelength of light. The dimensions of such modulators in the propagation direction are often in the centimeter range. Signal modulation via control of the waveguide absorption coefficient or refractive index is another possibility. However, this approach also requires substantial propagation lengths over which an amplitude or phase change accumulates, or it involves interferometric arrangements that are inherently longer than the wavelength of light. It has been suggested that strong signal modulation may be achieved in nanophotonic devices, despite very short propagation lengths, through the use of materials that show a substantial change in absorption or refraction in response to a control excitation: the relative change in the real and/or imaginary parts of the refractive coefficient must be of the order of unity and this can only be achieved in metals, where phase changes can bring about significant changes in optical properties. Such functionality has been extensively demonstrated with elemental gallium, which can exist in phases with radically different optical properties. In this case, phase changes lead to a modification of the plasmon and interband absorption to provide a platform for nanoscale active devices. 1-3Here we demonstrate another approach to nanoscale electro-optic modulation that relies not on absorption modulation but rather on a change in the refraction of a material associated with a control-input-induced phase change. In a layer of nanoscale thickness, such a refractive index change would be insufficient to noticeably modulate the intensity or phase of a transmitted wave. However, we demonstrate that by combining a nanoscale layer of phase-change material with a planar plasmonic metamaterial ͑Fig. 1͒ one can exploit the fact that the position of narrow resonant absorption lines in certain metamaterials are strongly dependent on the dielectric environment; switching the dielectric layer in contact with such a metamaterial produces a massive change in its resonance frequency. Importantly, ...

All-dielectric phase-change reconfigurable metasurface

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Photoinduced tunability of the reststrahlen band in4H−SiC

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