Total absorption for an ultrathin silicon grating within the low-loss mid-infrared window

Abstract To increase the absorption of silicon (Si)-based nanostructures within the loss window in the mid-infrared (MIR) range, periodic configuration which can efficiently couple the light into the supported optical modes have been proposed. In the first presentation, the absorption reaches a peak value of 99.6% at 3.162 μm wavelength with an ultra-narrow band. The absorber can be regarded as one-port resonant system with loss that can be explained through coupled mode theory (CMT). The influences of structure parameters on the absorption spectrum have been investigated in detail. In the second sample, vertically cascaded metal-dielectric-metal (MDM) grating structures are introduced to achieve dual-band selective absorbers. The underlying absorption mechanism of such perfect absorption effects at different resonant wavelength is attributed to the hybridization of cavity mode and guide mode resonance (GMR). These types of devices promise to impact the fields of solar thermophotovoltaics and sensing technologies with Si structures.