Multi-functional graphene-based tunable beam splitter in terahertz band

Two multi-functional graphene-based tunable beam splitters in terahertz band with different incidence modes are proposed in this paper. For the first time, we have achieved multiple functions of the beam splitter in the same structure only by tuning the Fermi level μc of the graphene layers. The optimum parameters are obtained through rigorous coupled-wave analysis, simulated annealing algorithm, and simplified modal method, which will be discussed in Section 2. At the optimum parameters, the proposed Littrow incidence beam splitter works as a polarization independent high-efficiency -1st order polarizer at μc=0ev and polarization independent uniform dual-port output beam splitter at μc=1.5ev. For normal incidence beam splitter, it can be transformed from a polarization independent 0th order suppressed dual-port output at μc=0ev to polarization-selective (transverse electric (TE)-two/transverse magnetic (TM) -three) output at μc=1.5ev. Moreover, the influence of the profile of the grating, the Fermi level, and the number of the graphene layers on diffraction efficiency are discussed in detail to reveal some manufacturing tolerances and the importance of choosing the specific appropriate parameters. The results indicate that the proposed multi-functional graphene-based tunable beam splitters in terahertz band with simple structure have great potential application values in the future.