  Impedance mismatch between free space and absorptive materials is a
fundamental issue plaguing the pursue of high-efficiency light absorption. In
this work, we design and numerically demonstrate a type of non-resonant
impedance-matched optical metasurfaces exhibiting ultra-broadband
reflectionless absorption based on anomalous Brewster effect, which are donated
as optical Brewster metasurfaces here. Interestingly, such Brewster
metasurfaces exhibit a unique type of extreme angular-asymmetry: a transition
between perfect transparency and perfect absorption appears when the sign of
the incident angle is changed. Such a remarkable phenomenon originates in the
coexistence of traditional and anomalous Brewster effects. Guidelines of
material selection based on an effective-medium description and strategies such
as the integration of a metal back-reflector or folded metasurfaces are
proposed to improve the absorption performance. Finally, a gradient optical
Brewster metasurface exhibiting ultra-broadband and near-omnidirectional
reflectionless absorption is demonstrated. Such high-efficiency asymmetric
optical metasurfaces may find applications in optoelectrical and thermal
devices like photodetectors, thermal emitters and photovoltaics.
