Modulation of mid-infrared light without spectral shift employing a graphene sheet and a magnetic plasmonic array

Abstract Graphene-based free-space optical modulators are usually enabled by shifting electrically the resonant frequency of a plasmonic or optical resonator. However, this resonance-shifting approach could lead to a potential loss of the on/off ratio, considering the fact that photodetectors always respond in a spectral range. Here, to modulate directly the amplitude of mid-infrared light, we propose a graphene-based modulator employing a graphene layer and a magnetic plasmonic array. With this novel design, the transmission intensity through the plasmonic array can be modulated in a direct manner without shifting the transmission peak. Magnetic plasmon resonance (MPR) accounts for the observed transmission, while Wood anomaly (WA) is utilized to fix the resonant position. The proposed modulator shows an excellent tolerance upon variation of structure parameters, with an insertion loss as low as 0.7 dB and a typical on/off ratio of 20, as well as a large modulation depth of 95%. This work offers a new route to design graphene-based optical modulators and may find applications in planar optics and the free-space optical (FSO) communication.