Surface Plasmon Polaritons in Time-Modulated Metallic Materials for Non-Reciprocal Controllable Leaky-Wave Antennas

In this work, we propose using time-modulation in metallic materials, which can be realized through either optical pumps or electric signals, as a coupling mechanism between radiation and surface plasmon polaritons (SPP) without using any optical component. By applying temporal changes in the permittivity of metallic materials, scattered waves yield different frequencies from incident waves, potentially satisfying the continuous wave vector condition and enabling SPP from radiation. The coupling is observed in finite-difference time-domain simulations, where the dispersive metallic materials are modeled using auxiliary differential equations. Under the same modulation, coupling from radiation to SPP and from SPP to radiation differ strongly, showing clear evidence of the non-reciprocity. In addition, the coupling is also actively controllable via strength and frequency modulation. We also demonstrate the coupling at multiple angles, which is difficult to achieve with common methods such as Kretschmann or Otto configurations. The direct and non-reciprocal coupling between radiation and SPP can be beneficial for the application of telecommunication to form transmitting-only and receiving-only leaky-wave antennas in full-duplex transceivers.