Broadband direction-dependent transmission of light with photonic crystal heterostructure grating

Abstract

Direction-dependent light transmission is a remarkable phenomenon owing to its great potential to be used in optical communication processing systems such as optical diodes, isolators and rectifiers. All these applications require optical reciprocity breaking mechanisms such as magneto-optical effect. Keeping the reciprocity intact, it is possible to manipulate the amount and spatial form of the two oppositely propagating lights exiting from a passive photonic medium. In this paper, a photonic crystal diffraction grating (PCDG) configuration is studied for the investigation of asymmetric light transport due to the spatial inversion symmetry breaking in the designed compact all-dielectric PC heterostructure. Thanks to the periodic corrugations at the back-surface of the designed structure, the backward transmission of the zero-order diffracted wave is notably suppressed while the efficient unidirectional forward transmission is achieved. Numerical calculations show that up to 73% of the incoming electromagnetic energy is transmitted in the forward illumination whereas it reduces down to a value of 6% (which corresponds to 10.85 dB beam suppression) in the case of backward illumination. That asymmetric light transmission leads to a contrast ratio (CR) of above 0.55 (CR = (T +x - T -x)/(T +x + T -x), in which T -x and T +x are the transmission efficiencies in the -x and +x directions, respectively). The highest contrast ratio of CR = 0.99 is calculated at the incident frequency of a/λ = 0.5338 having the forward and backward transmissions of {T +x,T -x} = {42%,0.1%}, which corresponds to the beam suppression of 26.23 dB. Furthermore, the proposed PCDG exhibits the diffraction grating effect at the considerable range of angle of incidence up to ±20° at certain frequencies indicating that the proposed grating system is durable to source misalignments.