Decreasing-width multilayers (DWMs) can behave as highly-efficient broadband reflectors with wider reflection spectrum than periodic, disordered or other aperiodic structures made of the same materials. In this article, we numerically analyze and optimize the reflectance R of a linear DWM formed by the bilayer
from normal to grazing incidence and for a large wavelength spectrum (from mid to far infrared). As a result, when the rate of the thickness decrease of
layers equals −59.5 nm/layer, an optimized average reflectance for
polarization
can be obtained in the 4–20 μm spectral range for all angles of incidence. For
incident states, the average reflectance is even greater
. Moreover, a near-zero transmittance region
occurs in the 12–20 μm wavelength interval constituting (to our knowledge) the widest spectrum for a single omnidirectional mirror where such remarkable reflectance values can be achieved.