Resonant Graphene-Based Tunable Optical Delay Line

Abstract

The design of a new graphene-based continuously tunable optical delay line formed by two vertically stacked microring resonators coupled to a straight waveguide is proposed. High values of delay time $(\tau_{g}=360 \mbox{ps})$ and a wide tuning range $(\mathit{\Delta}\tau_{g}=230 \mbox{ps} ) $ have been calculated, due to the graphene sandwiched between the stacked ring resonators, which also provides an electrooptical tuning of the delay with low energy consumption $(E_{\mathrm{switch}}=3.4 \mbox{pJ})$ and fast switching time $(t_{\mathrm{switch}} . The ratio $\mathit{\Delta}\tau_{g} /A$ represents an important figure of merit (FOM) for optical delay lines. A value $\mbox{FOM}=1.4\times 10^{-1} \mbox{ps}/\mu\mbox{m}^{2} $ has been calculated, which corresponds to an enhancement of about a factor 4 compared with the state-of-the-art of the integrated optical delay lines, also providing a switching time several times faster. Such performance, together with a small device footprint $( , gives a significant contribution to the state-of-the-art of optical delay lines, confirming the suitability of the graphene-based resonant cavity as a high-efficient optical delay line for applications in which fast tuning and wide range of tunability are required, e.g., phased array antennas.