Abstract
Electro-absorption modulators based on electrically contacted double-layer graphene optimally incorporated in plasmonic and photonic waveguide configurations were simulated and analyzed in terms of the device performance at telecom wavelengths. It is shown that increasing the mode electric field strength on the graphene layers enhances absorption of graphene and, in consequence, improves the electro-optic performances. The ratio of the change in extinction ratio and the waveguide loss (Delta alpha/alpha) is used as a figure of merit. A plasmonic waveguide configuration with a silicon ridge has a simulated 3 dB modulation depth for a device length of similar to 140 nm and Delta alpha/alpha similar to 20. The calculated energy consumption per bit is as low as similar to 240 aJ bit(-1) and similar to 1.8 aJ bit(-1) for plasmonic modulators with polymer and silicon ridge waveguides respectively. Much higher figures of merit were obtained for modulators based on photonic waveguides with Delta alpha/alpha exceeding 220 for a waveguide with a TM-supported mode. This comes at the cost of the modulator length, which increases to over 500 nm, and the calculated energy per bit of 1.93 fJ bit(-1) for polymer and similar to 10.3 aJ bit(-1) for silicon waveguides. The photonic waveguides were designed to support both TM and TE modes. The TE mode requires a much longer modulation length of similar to 10 mu m to achieve a 3 dB modulation depth and shows a lower figure of merit of similar to 12 compared to the TM mode, but has a low energy per bit of similar to 44.0 aJ bit(-1). The TE mode is in the OFF state at low applied voltage.