Real-time tunable phase response and group delay in broadside coupled split-ring resonators

Abstract

Manipulating the phase of electromagnetic radiation is of importance for applications ranging from communication to imaging. Here, real-time reconfigurable phase response and group delay of a tunable terahertz metamaterial consisting of dual-layer broadside coupled split-ring resonators is demonstrated. Utilizing electrostatic comb-drive actuators, the metamaterial resonant frequency is tuned by changing the lateral distance between the two layers which modifies the transmission amplitude and phase spectrum. The phase modulation is approximately 180\ifmmode \mathring{}\else \r{}\fi{} in the vicinity of the resonant frequency. In addition, remarkable modulation in the group delay of transmitted pulses (from \ensuremath{-}7 to 3 ps) is evaluated based on the measured frequency response using the convolution method when the lateral distance is changed from 0 to $24\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{m}$. A two-port resonator model, derived from coupled-mode theory and supported by finite-element full-wave simulations, reveals the underlying physics of the modulation. Specifically, the coupling factor between the two layers plays a critical role, the tuning of which provides a route for structure design and optimization. The capability of tuning the phase response and group delay enables applications, such as phase compensation and group-delay equalization at terahertz frequencies.