Extraordinary wavelength reduction in terahertz graphene-cladded photonic crystal slabs

摘要

Photonic crystal slabs have been widely used in nanophotonics for lightconfinement, dispersion engineering, nonlinearity enhancement, and otherunusual effects arising from their structural periodicity. Sub-micron devicesizes and mode volumes are routine for silicon-based photonic crystal slabs,however spectrally they are limited to operate in the near infrared. Here, weshow that two single-layer graphene sheets allow silicon photonic crystal slabswith submicron periodicity to operate in the terahertz regime, with an extreme100x wavelength reduction and excellent out-of-plane confinement. Thegraphene-cladded photonic crystal slabs exhibit band structures closelyresembling those of ideal two-dimensional photonic crystals, with broadtwo-dimensional photonic band gaps even when the slab thickness approacheszero. The overall photonic band structure not only scales with the grapheneFermi level, but more importantly scales to lower frequencies with reduced slabthickness. Just like ideal 2D photonic crystals, graphene-cladded photoniccrystal slabs confine light along line defects, forming waveguides with thepropagation lengths on the order of tens of lattice constants. The proposedstructure opens up the possibility to dramatically reduce the size of terahertzphotonic systems by orders of magnitude.