Extended slow-light field enhancement in positive-index/negative-index heterostructures

We present a biwaveguide paradigm composed of joined positive-index- material (PIM)/negative-index-material (NIM) slabs, demonstrating ultraslow-light propagation stemming from the competing propagation disposition in the PIM and NIM regions. We report for the first time a mesoscopic extended electromagnetic (EM) enhancement covering regions of the order of the free-space wavelength, enabled by the slow-light mode in our system. Our dynamic numerical results are consistent with our developed theoretical model, predicting an EM energy accumulation reminiscent of a charging capacitor. Our analysis reveals that spatial compression is not a requirement for EM enhancement in slow-light systems and stresses the merits of a high coupling efficiency, strong temporal compression, monomodality, and modal index bandwidth - all present in our proposed paradigm. Furthermore, we show that the heterostructure waveguide mode is an extraordinary entity with a unique energy velocity, which is opposite to the Poynting vector in one of the participant waveguides. We believe that these results will inspire new slow-light platforms relevant to the collective harvesting of strong light-matter interactions.