Active tuning of ENZ resonances in meta-antenna through phase modulation of optical pulse

TL;DR

Authors address the challenge of dynamically tuning ENZ resonances in plasmonic metasurfaces without using natural ENZ materials, aiming for ultrafast, reconfigurable on-chip photonic functionality. Approach combines a pump–probe scheme with two coupled L-shaped Ag nanoantennas where the phase $\phi$ of the pump relative to the probe controls local field enhancement and the ENZ response through a quantum-mechanical Hamiltonian model and 3D FDTD simulations. Key results show that varying $\phi$ induces measurable spectral shifts of the ENZ frequency in both linear and nonlinear regimes, with a regime of zero absorption at the ENZ point. This phase-controlled tuning is reversible and persists after the pump is switched off, suggesting practical use in photonic integrated circuits, metasurfaces, and quantum technologies.

Abstract

Plasmonic nanoantennas offer new avenues to manipulate the propagation of light in materials due to their near field enhancement and ultrafast response time. Here we investigate the epsilon-near-zero (ENZ) response in an L-shaped nanoantenna structure under the phenomenon of plasmonic analog of enhancement in the index of refraction. Using a quantum mechanical approach, we analyze the modulation in the response of probe field and emergence of ENZ frequency region both in the linear and nonlinear plasmonic system. We also demonstrate the active tuning of ENZ frequency region in a nanoantenna structure by modulating the phase of control pulse. The analytical and 3D FDTD simulation results show a significant spectral shift in the ENZ modes. Our proposed method offers the possibility to design and control optical tunable ENZ response in plasmonic metasurfaces without the use of ENZ material. Such metasurfaces can be used in on-chip photonic integrated circuits, further localization of incident fields, slow light operations and various quantum technologies.

Figures (5)

• Figure 1: Schematic diagram of plasmonic metasurface with nanoantenna structure supporting the ENZ response. In a pump-probe setup, an L-shaped plasmonic antenna
• Figure 2: (a,b) Real and imaginary part of electric susceptibility in NE$_2$ demonstrating the enhanced EIR as a function of normalized frequency. At point A, absorption is zero and at A$^{,}$ the susceptibility [Re$\{\chi\}<-17$] becomes negative indicating the point of ENZ frequency.
• Figure 3: (a,b) Electric polarization in NE$_2$ demonstrating the intensity of linear and nonlinear plasmon mode as a function of normalized frequency for various phases ($\phi$) of control pulse. Results are evaluated through FDTD simulations.
• Figure 4: Real part of susceptibility $\chi(\omega)$ in the (a) linear and (b) nonlinear regime as a function of normalized frequency for various phases ($\phi$) of control pulse. Results are obtained using FDTD simulations. (add imag parts here)
• Figure 5: Modulation in ENZ frequency in (a) linear and (b) nonlinear plasmonic systems for different control phases.