Generating Fano Resonances in a Single-Waveguide Silicon Nanobeam Cavity for Efficient Electro-Optical Modulation

Abstract

A method for generating Fano resonance in a standalone silicon nanobeam cavity is reported and investigated thoroughly. The proposed approach eliminates the inconvenience from the unexpected side-coupled bus waveguide of previous Fano cavity geometries and unlocks new opportunities to develop ultracompact and ultrafast silicon electro-optical modulators. Taking advantage from a spatial-division multiplexing principle of operation between transverse electric modes, a sharp resonant mode and an efficient flat background mode are simultaneously generated in the same silicon channel for the realization of efficient Fano resonances. Unambiguous asymmetric spectral line shapes are experimentally demonstrated in the near-infrared around λ = 1.55 μm correlated to analytical and numerical methods. The best identified mode for optical modulation presents an extinction ratio of 23 dB for a Δλ = 366 pm wavelength detuning, while its Q factor is limited to only 5600. For the same wavelength detuning, this extinction ratio is ∼14 dB higher than that of the classical Lorentzian cavity exhibiting the same Q factor. Electro-optical modulation based on the silicon Fano cavity and exploiting the plasma dispersion effect is proposed and quantitatively studied, showing energy consumption as low as few fJ/bit. The overall gathered results show that the proposed Fano cavity scheme addressed in this paper presents an interesting potential for low-power-consumption silicon electro-optical modulation and provides new insight into the advantages and applications of Fano resonances in nanophotonics.