Strong coupling of a surface grating to a structurally chiral volume grating

The problem of coupling a surface dielectric grating consisting of a sinusoidal corrugation to a structurally chiral volume grating has been formulated and solved with results showing the robust co-existence of phenomena characteristic of both types of grating: namely Rayleigh-Wood anomalies and Bragg zones. A mechanism to strengthen the coupling between both grating types has now been included in the model, namely a quarter wave plate whose birefringence converts normally incident linearly polarised light of the chiral Bragg wavelength into transmitted circularly polarised light. It is possible to tailor the period of the sinusoidal surface grating such that the scattering of obliquely incident light from above, by the surface grating, will lead to a specific non-zero order being scattered onto a path which is normally incident on the rest of the structure. Significantly, such orders exhibit the circular Bragg phenomenon in reflection and transmission only if both grating types are present, making this a truly coupled grating effect.