Fundamental limits and near-optimal design of graphene modulators and non-reciprocal devices

Abstract

The potential of graphene for use in photonic applications was evidenced by recent demonstrations of modulators, polarisation rotators, and isolators. These promising yet preliminary results raise crucial questions: what is the optimal performance achievable by more complex designs using multilayer structures, graphene patterning, metal additions, or a combination of these approaches, and how can this optimum design be achieved in practice? Today, the complexity of the problem, which is magnified by the variability in graphene parameters, leaves the design of these new devices to time-consuming and suboptimal trial-and-error procedures. We address this issue by first demonstrating that the relevant figures of merit for the devices above are subject to absolute theoretical upper bounds. Strikingly these limits are related only to the conductivity tensor of graphene; thus, we can provide essential roadmap information such as the best possible device performance versus wavelength and graphene quality. Second, based on the theory developed, physical insight, and detailed simulations, we demonstrate how structures closely approaching these fundamental limits can be designed, demonstrating the possibility of significant improvement. These results are believed to be of paramount importance for the design of graphene-based modulators, rotators, and isolators and are also directly applicable to other 2-dimensional materials.In recent years, there has been a surge of interest in graphene-based devices for various photonic and optoelectronic applications 1-15 . Among other very promising passive devices, including amplitude modulators 5, 16-23 , Faraday and Kerr polarisation rotators 24-26 , and non-reciprocal isolators 27,28 have been demonstrated. These essential photonic blocks might constitute some of the most important applications of graphene; thus, there is a significant and growing effort to transform the above-mentioned initial demonstrations into real capabilities. However, this prospect still requires drastic performance improvements. For this purpose, researchers have now started to develop graphene-based devices with multiple degrees of freedom by considering several technological solutions (see Figure 1e), including multilayer structures 22, 29, 30 , graphene patterning 7, 22, 25, 31 , substrate engineering, and combining metal and graphene 13,14,18,21,29,32 .

Unidirectional terahertz light absorption in the pyroelectric ferrimagnetCaBaCo4O7

“…one-way light guides and polarization rotators. The largest directional dichroism in multiferroics is at terahertz (THz) frequencies [11] what can boost terahertz photonics in the future, similar to the prospect of graphene non-reciprocal terahertz devices [15]. The dc and the finite frequency ME effect, which determine the efficiency of any multiferroic device, are intimately connected by a sum rule [16] allowing a large static ME effect only if a large non-reciprocal directional dichroism is present in the absorption spectrum of electromagnetic radiation.…”

Comparison of gold- and graphene-based resonant nanostructures for terahertz metamaterials and an ultrathin graphene-based modulator

“…We revealed that the huge kinetic inductance of graphene allows to achieve resonant response in the deep sub-wavelength limit under normal incidence when the kinetic inductance dominates. However, the high dissipative loss of state-of-the-art 40 Here, we propose a prototype design of THz switch based on a metamaterial with a multi-layer stack of patterned graphene [shown in Fig. 5(a) for a two-layer configuration], the modulation effect of which will be shown purely due to the resonant property of graphene metamaterial itself.…”

Chip-integrated all-optical diode based on nonlinear plasmonic nanocavities covered with multicomponent nanocomposite

“…For the practical on-chip integration applications, the all-optical diode should possess the following key characteristics: ultrasmall feature size, ultralow threshold power, high isolation ratio, and on-chip trigger [2,3]. The basic idea of realizing chip-integrated all-optical diode is to break the time-reversal symmetry by using indirect interband photonic transition [4][5][6][7], angular-momentum biasing [8], magneto-optic effect [9][10][11][12][13][14], third-order optical nonlinearity [15][16][17][18], in dielectric photonic microstructures with broken spatial-reversal symmetry, including asymmetric photonic crystal heterostructures and asymmetric silicon ring resonators [19,20]. The large size of dielectric photonic microstructures limits the practical on-chip integration applications of an all-optical diode [21].…”