An ultra-narrowband absorber with a compound dielectric grating and metal substrate

We propose an alternative method to achieve an ultra-narrowband absorber with a single-layer compound dielectric structure and metal substrate. The simulation results show that the absorption bandwidth is 1.3 nm and the absorption rate is more than 0.99 for TE polarization (electric field is parallel to grating grooves). The phase resonance plays an active role in the resonance absorption. Furthermore, the electric field is mainly distributed in the grating grooves. The figure of merit (FOM) is larger than 480 if this absorber is applied as a refractive index sensor.