Simple-modal and leaky-modal field signatures in photonic lattices

Localized field patterns appearing within one-dimensional resonant photonic lattices (PLs) are often interpreted as deriving from Fabry–Perot (FP) or Mie resonances. Applying rigorous numerical methods, we show that these patterns originate simply from the superposition of guided slab modes. This applies both for nonresonant edge coupling and broadside resonance coupling. For a model PL supporting guided-mode resonance, we characterize edge-coupled modes at the frequencies where leaky modes are excited. The resulting field distributions approximate those observed in guided-mode resonance, confirming that the patterns arise from coherent superposition of guided modes in both cases. Dual-edge excitation producing counterpropagating modes as in guided-mode resonance reproduces Bloch-like standing-wave fields equivalent to those observed under free-space broadside illumination. Taking a PL incorporating an antireflection film, we show that similar local field signatures appear in resonant PLs when FP resonances are eliminated. Finally, using a design with all potential particle resonances forbidden, we show that the principal resonance spectra persist. In summary, the physics of metamaterials comprising resonant subwavelength PLs is grounded in lateral leaky Bloch modes and plane-wave reradiation without causal contributions by local particle resonance.