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 ðg ¼ 360 psÞ and a wide tuning range ðg ¼ 230 psÞ 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 ðEswitch ¼ 3:4 pJÞ and fast switching time ðtswitch G 2 nsÞ. The ratio g=A represents an important figure of merit (FOM) for optical delay lines. A value FOM ¼ 1:4 101 ps=m2 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 ðG 1:6 103 m2Þ, 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.