Enhanced strong confinement in low refractive index photonic crystal slab using bound states in the continuum and its interaction with TMDCs

Radiative losses in nanophotonic devices are a fundamental challenge in their miniaturization. Plasmonic metals overcome the radiation losses, but high ohmic losses hinder the optical performance. Bound states in the continuum (BIC), help circumvent this problem. In this work, we propose a low refractive index polymeric 2D-periodic slab that supports symmetry protected BIC and accidental BIC at off-gamma point. This BIC point is very fascinating to study the exciton-cavity interaction. To study the exciton-cavity, TMDCs have the great potential to generate the exciton. This exciton is coupled with BIC mode to generate the polariton state in a strong coupling region.

First, we optimize the parameters 2D photonic slab to exhibit the BIC mode at the exciton frequency of transition metal dichalcogenide (TMDC) monolayer. We calculate the photonic bandgap using a guided mode expansion method. We further confirm the BIC mode by calculating the Q-factor of each mode. After optimizing the structure we study the exciton interaction between this BIC mode and WS2 monolayer.

This strong coupling regime can be used in many cutting edge applications like coherent perfect absorption, dark exciton emission at room temperature etc.