Design optimization of single and double layer Graphene phase modulators in SOI

Abstract

In this paper we report on an electro-refractive modulator based on single or double-layer graphene on top of silicon waveguides. The graphene layers are biased to the transparency condition in order to achieve phase modulation with negligible amplitude modulation. By means of a detailed study of both the electrical and optical properties of graphene and silicon, as well as through optimization of the geometrical parameters, we show that the proposed devices may theoretically outperform existing modulators both in terms of V(π)L and of insertion losses. The overall figures of merit of the proposed devices are as low as 8.5 and 2dB∙V for the single and double layer cases, respectively.

Chirp management in silicon-graphene electro absorption modulators

“…In particular, both SLG and Si induce a reduction of the effective index when populated by carriers. As we demonstrated in a previous work [21], the SLG offers the main contribution to the effective index change, while Si is responsible of about 1/3 of the overall effect. Moreover, larger effect is expected in the double layer Graphene modulator, where the voltage is applied between the SLG on top of an undoped Si waveguide.…”

“…We can observe that, as the voltage applied to the SIG capacitor increases, carriers accumulate on the SLG causing the shift of Fermi level towards higher energies [21]. When the Graphene Fermi level is driven beyond the Pauli blocking condition (> 0.4 eV at 1550 nm), the effective refraction index change, and the optical transmissivity have an opposite dependence with respect to the applied voltage: this means that the optical signal phase decreases when the transmitted power increases.…”

“…Moreover, larger effect is expected in the double layer Graphene modulator, where the voltage is applied between the SLG on top of an undoped Si waveguide. In such device, the effective index variation is roughly improved by a factor of two [21], which means that a larger chirp would be obtained.…”

Capacitive actuation and switching of add–drop graphene-silicon micro-ring filters

“…Conversely, when μ > ℏω∕2, optical absorption drops down and bounds to a minimum level that is strongly affected by the intra-band scattering mechanisms [16] (∼48 to ∼175 dB∕cm for τ 300 and 30 fs). The effective index slowly decreases when μ < ℏω∕2, then increases with a peak at μ ∼ ℏω∕2, and then monotonically decreases for increasing Fermi level in the low-loss region for μ > ℏω∕2.…”

“…The applied voltage will result as the sum of two terms: the first is the potential across the capacitor dielectric, the second is due to the Fermi potential shift induced by the accumulated carriers on the graphene layer. This relation is expressed as [16] …”