Resonant Graphene-Based Tunable Optical Delay Line

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 (τ_g = 360 ps) and a wide tuning range (Δτ_g = 230 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_switch = 3.4 pJ) and fast switching time (t_switch <; 2 ns). The ratio Δrg/A represents an important figure of merit (FOM) for optical delay lines. A value FOM = 1.4 × 10^-1 ps/μm² 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 (<; 1.6 × 10³ μm²), 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.