Strong frequency-dependent beam steering dynamics, Zitterbewegung effect, and Klein tunneling in a ternary plasmonic-dielectric superlattice

Abstract

Band structures are intrinsically influenced by the mode interaction in waveguide array, which can support many intriguing phenomena such as negative refraction, on-chip lensing, and quantum-analog dynamics like Bloch oscillation and topological interface transportation. Multiple branches of band may emerge due to the comprehensive mode interactions associated with high-order photonic modes supported in high refractive index dielectric waveguide. Furthermore, the number of photonic modes confined in a high-index waveguide is determined by both the width and working frequency. Hence, the mode interaction and resultant band structure can be effectively tuned by the frequency. As such, a diversity of equifrequency contours could be generated and modulated among a wide frequency range, which, however, remains largely unexplored. Here, we present several frequency-determined beam dynamics in a composite ternary plasmonic-dielectric waveguide array, including collimation effect, angle-dependent beam branching/multibranching, conicallike beam diffraction. Based on the evolution of the band structure, photonic Zitterbewegung effect and Klein tunneling can also be observed. In contrast to the coherent coupling between symmetric and antisymmetric modes that gives rise to the photonic Zitterbewegung effect, we show that three-mode coherent coupling in the ternary system can yield a superimposed extreme oscillation of the beam. This represents an extension of the general Zitterbewegung effect in photonic system. Additionally, the Klein tunneling sandwiched in two types of artificial waveguide arrays with different Dirac points is demonstrated, and approximately unimpeded penetration is exhibited. The configurations discussed here can be readily implemented in on-chip systems for a variety of potential applications including wave routing, selectively directional coupling, and multiplexing.