Graphene is a two-dimensional material, manifests good photoelectricity performance and flexible tunability. Comparing with traditional metal multilayers, graphene multilayers possess more advantages. The SPPs in graphene possess huge mode localization and low propagation loss in far infrared regions. Meanwhile, graphene manifests kerr nonlinearity. By taking advantage of graphene, the propagation of SPPs can be manipulated very well.

The Prof. Bing Wang of ultrafast optics group has presented the nonlinear graphene multilayers composed of arbitrary layers of graphene to excite the supermodes of SPPs. Apart from the symmetric and anti-symmetric supermodes which exist in linear multilayer graphene waveguides, more asymmetric supermodes emerge in the nonlinear counterparts as the field symmetry is broken. All supermodes can propagate steadily in the structure with the mode profile remains fairly constant. There is a certain threshold of field intensity for the emergence of each individual asymmetric supermode. The dependence of the intensity threshold to yield asymmetric supermodes on the wavelength and chemical potential is also discussed. The study may find applications in developing all-optical converters and switches on the deep-subwavelength scale.

This work is supported by the 973 Program (No. 2014CB921301), the National Natural Science Foundation of China (Nos. 11304108 and 11674117), and the Specialized Research Fund for the Doctoral Program of Higher Education of China (No. 20130142120091).

Fig. 1. (a) Mode profiles of four supermodes as N = 3. (b) Mode profiles of six supermodes as N = 4.

Fig. 2. Electric field intensity distribution of the supermodes in the nonlinear graphene multilayer as N = 4.