ECE PhD Proposal Review: Ziqiang Cai

PhD Proposal Review: Near-infrared Optical Modulation by Hybrid Graphene Metasurfaces

Ziqiang Cai

Location: Zoom Link

Abstract: The field of metasurfaces has emerged as one of the most promising frontiers in optical research due to the compact footprint and flexibility in light manipulation. To further advance the practical applications of metasurfaces, tunable or reconfigurable metasurfaces are highly desirable. One approach is to utilize graphene by taking advantage of its tunable optical properties upon electrical bias. Graphene metasurfaces have been extensively studied in many applications, including polarization tuning, phase tuning, photodetectors, chemical sensing, tunable lens, etc. However, the working wavelengths of the reported graphene metasurfaces are limited in mid-infrared and terahertz spectra.
In this proposal review, I will discuss a graphene metasurface that can push the working wavelength into the near-infrared region (≤ 3.0 µm). The device combines graphene with plasmonic structures made of gold to enhance the interband transition of graphene, resulting in decent tunability at near-infrared wavelengths. The tuning process of our graphene metasurface shows distinct differences in comparison with the graphene metasurfaces operating in the mid-infrared or terahertz spectra, which can be accurately predicted by both theory and simulation. The measured results show a reflection modulation ΔR of about 10% and a modulation depth ΔR/Rmax of 17% at 2.42 µm.
Finally, by using an anisotropic plasmonic structure, our hybrid graphene metasurface can simultaneously operate in the near-infrared and mid-infrared spectra. The measured modulation depth is 18.2% at 2.30 µm and 24.7% at 5.67 µm. Our research substantially broadens the working wavelength of graphene metasurfaces, and manifest potential applications in near-infrared electro-optic modulators, reconfigurable lenses, and polarization modulators.