High-Capacity and Dispersionless Delay Lines Based on Plasmonic Waveguide Periodically Coupled With Bilaterally Located Ring and Slot Resonators

We propose and study optical delay lines with high capacity and low dispersion based on a plasmonic waveguide periodically coupled with bilaterally located ring and slot resonators. The repetitive unit exhibits plasmon-induced transparency (PIT) with a large delay-bandwidth product due to the interference between the two-mode ring and single-mode slot resonators. By choosing appropriate parameters, the cascaded PIT units can possess a broad transparency window with moderate fluctuations and produce wideband dispersionless slow light. A theoretical model is developed to analyze the proposed structure and the results are validated by finite-difference time-domain simulations. The pulse propagation results indicate that the spectral fluctuations have a negligible effect on the delayed pulse shape. Using multiple cascaded PIT units, we demonstrate that the group index of the waveguide approaches 36, the 3-dB bandwidth is larger than 21 nm, and a storage efficiency of 0.5 bit/unit can be realized with negligible distortion. Due to the high performance, the proposed delay line may find potential applications in future nanoscale integrated photonic systems.