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. 2017 Jul 12;7(1):5190.
doi: 10.1038/s41598-017-05172-9.

Tunable Graphene-Based Hybrid Plasmonic Modulators for Subwavelength Confinement

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Free PMC article

Tunable Graphene-Based Hybrid Plasmonic Modulators for Subwavelength Confinement

Sheng Qu et al. Sci Rep. .
Free PMC article

Abstract

Electro-optical modulators which work at the near-infrared range are significant for a variety of applications such as communication and sensing. However, currently available approaches result in rather bulky devices which suffer from low integration and can hardly operate at low power consumption levels. Graphene, an emerging advanced material, has been widely utilized due to its tunability by gating which allows one to realize active optical devices. Plasmonic waveguides, one of the most promising candidates for subwavelength optical confinement, provide a way to manipulate light on scales much smaller than the wavelength. In this paper, we combine the advantages of graphene and plasmonic waveguides and propose a tunable graphene-based hybrid plasmonic modulator (GHPM). Considering several parameters of the GHPM, the modulation depth can reach approximately 0.3 dB·μm-1 at low gating voltages. Moreover, we combine GHPM with metal-insulator-metal (MIM) structure to propose another symmetrical GHPM with a modulation depth of 0.6 dB·μm-1. Our modulators which utilize the light-matter interaction tuned by electro-doped graphene are of great potential for many applications in nanophotonics.

Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Figure 1
Figure 1
Plasmon dispersion of monolayer graphene when the graphene is doped (For clarify, here we use highly doped graphene with E F = 1 eV.), as illustrated by the photon-energy and parallel-wave-vector dependence of the imaginary part of reflection coefficient for p-polarization. Interband absorption produces strong plasmon quenching when the photon energy exceeds 2E F (i.e., above the yellow dash line).
Figure 2
Figure 2
The refractive index of monolayer graphene varies with the Fermi energy (details see Methods). The black line and the red line represent the real part and imaginary part of the refractive index, respectively.
Figure 3
Figure 3
The structure and mode distributions of the designed GHPM. (a) Three dimensional structure and cross section of the proposed hybrid modulator. (b) The mode distributions of the designed modulator at a 1550 nm wavelength where d = 200 nm, h = 4 nm and hd = 50 nm.
Figure 4
Figure 4
The modulation depth of GHPM varies with the cylinder diameter d, the dielectric gap thickness h and the silicon slab thickness hd, respectively. (a) The cylinder diameter d varies from 100 to 300 nm where h = 4 nm and hd = 50 nm. (b) The gap thickness h varies from 2 to 8 nm where d = 200 nm and hd = 50 nm. (c) The silicon slab thickness hd varies from 20 to 80 nm where d = 200 nm and h = 4 nm. (d) The modulation process of GHPM is achieved for a broad band of wavelengths from 1350 nm to 1600 nm.
Figure 5
Figure 5
The structure and mode distributions of SGHPM. (a) Three dimensional structure of the hybrid modulator. (b) The mode distributions of the designed modulator at the wavelength of 1550 nm where d = 200 nm, h = 4 nm and hd = 50 nm.
Figure 6
Figure 6
The modulation depth of SGHPM varies with the cylinder diameter d, the dielectric gap thickness h and the silicon slab thickness hd, respectively. (a) The cylinder diameter d varies from 100 to 300 nm where h = 4 nm and hd = 50 nm. (b) The gap thickness h varies from 2 to 8 nm where d = 200 nm and hd = 50 nm. (c) The silicon slab thickness hd varies from 20 to 80 nm where d = 200 nm and h = 4 nm. (d) The modulation process of SGHPM is achieved for a broad band of wavelengths from 1350 nm to 1600 nm.
Figure 7
Figure 7
The normalized effective mode area (A eff  /A 0) varies with the cylinder diameter d and the dielectric gap thickness h for the GHPM (black lines) and SGHPM (red lines), respectively. (a) The cylinder diameter d varies from 100 to 300 nm where h = 4 nm and hd = 50 nm. (b) The dielectric gap thickness h varies from 2 to 8 nm where d = 200 nm and hd = 50 nm.

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