Abstract
Unidirectionally propagating wave (UPW) such as surface magnetoplasmon (SMP) has been a research hotspot in the last decades. In the study of the UPW, metals are usually treated as perfect electric conductors (PECs). However, it was reported that the transverse resonance condition induced by the PEC wall(s) may significantly narrow up the complete one-way propagation (COWP) band. In this paper, ultra-broadband one-way waveguides are built by utilizing the epsilon-negative (ENG) metamaterial (MM) and/or the perfect magnetic conductor (PMC) boundary. In both cases, the total bandwidth of the COWP bands are efficiently enlarged by more than three times than the one in the original metal-dielectric-semiconductor-metal structure. Moreover, the one-way waveguides consisting of gradient-index metamaterial are proposed to achieve broadband truly rainbow trapping (TRT). In the full-wave simulations, clear broadband TRT without back reflection is observed in terahertz regime. Besides, giant electric field enhancement is achieved in a PMC-based one-way structure, and the amplitude of the electric field is enormously enhanced by five orders of magnitude. Our findings are beneficial for researches on broadband terahertz communication, energy harvesting and strong-field devices.
Highlights
Unidirectional or one-way electromagnetic (EM) modes attract more and more attentions in the past two decades [1,2,3,4,5] for its unique unidirectional propagation property which has extensive applications in optical communication
Besides the complete one-way propagation (COWP) 1 band, the COWP 2 band shown in Fig. 5(e) is changed to a band gap (BG) when εm changes from 11.68 to −5, which implies that similar truly rainbow trapping (TRT) may be achieved in the COWP 2 band
ENG MMs and perfect magnetic conductor (PMC) walls can be used to design ultra-broadband one-way waveguide since the electromagnetic modes sustained on the semiconductor-metal interface (SMs) in the ENG- or PMC-based structures become unidirectional whereas the SMs in the regular one-way waveguides always suffer from the reverse propagating surface magnetoplasmon (SMP)
Summary
Unidirectional or one-way electromagnetic (EM) modes attract more and more attentions in the past two decades [1,2,3,4,5] for its unique unidirectional propagation property which has extensive applications in optical communication. Engineering the band diagram of photonic crystals (PhCs) by introducing disorders is an efficient way to build one-way waveguide [2,8,9], and the cells of PhCs always consist of magneto-optical (MO) materials under a static magnetic field which is exploited to break the time-reversal symmetry of the system. Numerous applications such as optical splitter [10,11,12], subwavelength focusing [13,14,15] and optical switch [16] were proposed based on the one-way waveguides. All the theoretical analysis are verified by simulations utilizing finite element method
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