Electromagnetically induced transparency analogue and slow light effect in an asymmetric plasma waveguide

Electromagnetically induced transparency (EIT), characterised by strong dispersion and a narrow transparency window, holds great potential for developing slow light devices in communications. However, in the GHz regime, achieving a simple EIT structure with high group delay and tunability remains challenging. This paper reports an asymmetric plasma waveguide capable of producing EIT analogues, as demonstrated by finite element method simulations and a two-oscillator model (TOM). The asymmetric plasma waveguide consists of a plasma-dielectric-plasma structure with non-uniformly sized teeth. The results indicate that the EIT analogue is attributed to detuning induced by the difference in tooth size. Specifically, the detuning creates an interference band, which governs the interaction between two bright modes (i.e. resonance modes in the two teeth). The TOM aligns excellently with numerical simulations. Notably, unlike previous works, the TOM is also analysed from a fundamental energy perspective. The operating frequency can be easily tuned by adjusting plasma frequencies. The maximum group delay can reach 8.5 ns. Our study advances the understanding of the EIT phenomenon in slot waveguides with asymmetric resonators and may offer a new platform for developing actively tunable microwave slow-light devices.