Energy-efficient high-speed optical modulators based on the interplay of epsilon-near-zero effect in graphene and ITO

The epsilon-near-zero effect of graphene and indium-doped tin oxide (ITO) is combined in an optical waveguide with a metal–oxide–semiconductor arrangement to provide the possibility of effective, high-speed optical modulation with low power consumption. The active waveguide is designed to induce large variations in the real and imaginary parts of the effective refractive index with an applied voltage. The proposed active waveguide is then used to design absorption and Mach–Zehnder optical modulators to perform binary and also 4- and 16-point quadrature amplitude modulation (4QAM and 16QAM). All modulators were optimized for operation at a wavelength of 1550 nm. It was shown that the proposed absorption modulator has an extinction ratio (ER) of 9.5 dB, an insertion loss (IL) of 1.4 dB, and an energy consumption of 1.57 fJ/bit. Using the Mach–Zehnder structure, binary, 4QAM, and 16QAM modulators with small active lengths of 0.6907 µm, 0.34536 µm, and 1.58 µm, respectively, are achieved. The binary modulator has an ER of 4.9 dB, an IL of 0.4 dB, an energy consumption of 6.17 fJ/bit, and the V π L π figure of merit of 0.55 V. µm. For the 4QAM/16QAM modulators, IL, energy consumption, and the achievable bit rate are estimated to be 1.45/9.64 dB, 0.05/0.113 fJ/bit, and 500/1000 Gbit/s, respectively.