A giant field enhancement factor, defined as the ratio between the intensity of the resonant and the incident fields, is achievable in a photonic crystal (PhC) slab realized in a low contrast dielectric medium. The key point is the careful control of some parameters, first among all the slab thicknesses, which allows for stabilizing the coupling resonant mechanism. These modes are closely correlated with symmetry-protected bound states in continuum. Our study proves, in frequency as in time domain, that such modes can be excited with a normal incident beam and that the giant resonant enhanced field starts to grow and is established after more than ${10}^5\text{−}\mathrm{cycle}$ time. Up to six orders of magnitude of field enhancement distributed along all the slab is achievable, making it easier to use in many applications than localized enhancement.

• Received 28 April 2015
• Revised 15 September 2015

DOI:https://doi.org/10.1103/PhysRevB.92.155117