Necklace State Hallmark in Disordered 2D Photonic Systems

Necklace states arise from the coupling of otherwise confined modes in disordered photonic systems and open high transmission channels in strongly scattering media. Despite their potential relevance in the transport properties of photonic systems, necklace state statistical occurrence in dimensions higher than one is hard to measure, because of the lack of a decisive signature. In this work we provide an efficient method to tell apart in a single measurement a coupled mode from a single localized state in a complex scattering problem, exploiting the analogy with well-characterized coupled cavities in photonic crystals. The phase spatial distribution of the electromagnetic field has been numerically calculated and analyzed as a function of the coupling strength and of detuning between interacting modes respectively for coupled photonic crystal cavities and for partially disordered systems. Results consistently show that when localized modes spectrally and spatially overlap only over a small surface extent, synchronous oscillation does not build up and the phase spatial distribution splits into two distinct peaks. Having established such bimodal distribution as a necklace hallmark, this paper opens the possibility to assess and eventually tailor the role of necklace states in random systems, e.g., by varying correlations.