Abstract
Here we demonstrate directional excitation and asymmetric reflection by using parity-time (PT) symmetric and zero index metamaterials (ZIMs) in a three-port waveguide system. The principle lies on that the field distribution at gain/ loss interface is significantly affected by the incident direction of electromagnetic wave. By taking advantage of the empty volume feature of ZIMs, these asymmetric effects are extended to a more general three-port waveguide system. In addition, by exciting a weak modulated signal in branch port in our proposed design, unidirectional transmission with an unbroken propagation state is achieved, opening up a new way distinguished from the present technologies.
Highlights
In the past years, asymmetric effects, such as asymmetric transmission, have drawn much attention in numerous research domains
By exciting a weak modulated signal in port 3, we find that unidirectional transmission with an unbroken propagation state of light is achieved in the main waveguide, which stands out from that realized by breaking spatial symmetry[35,36,37,38]
Let us start from the considered three-port waveguide structure shown in Fig. 1(a), where the red and blue sections represent the gain medium and loss medium, respectively, separated by a zero index metamaterials (ZIMs) layer
Summary
Asymmetric effects, such as asymmetric transmission, have drawn much attention in numerous research domains. Because the third port (port 3) is opened at the gain/loss layer interface, there will be highly asymmetric field coupled to it. Such directional excitation can only work for a limited case, i.e., the width of port 3 is much narrower than that in the main waveguide. For port 3 with narrower width, only a little wave energy can be squeezed into port 3, which limits the performance of directional excitation. We will demonstrate that the directional excitation and asymmetric reflection can be realized in our proposed ZIM waveguide system with PT symmetry, where the port 3 can possess a wider width. By exciting a weak modulated signal in port 3, we find that unidirectional transmission with an unbroken propagation state of light is achieved in the main waveguide, which stands out from that realized by breaking spatial symmetry[35,36,37,38]
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