“…Besides conventional AR layers made of transparent materials (19,20), AR coatings (ARCs) incorporating absorbing materials (called absorbing ARCs) were introduced when AR properties and light absorption or attenuation were needed (21)(22)(23). These coatings can be either settled on opaque reflective substrates or made of multilayer stacks of absorbing materials and transparent AR layers, and, in all cases, they are used in the "frontside" configuration (that is, the coated surface facing the observer with the light going from the low-index to the high index mediafor example, air to glass) (21,(24)(25)(26)(27)(28). However, absorbing ARCs exhibit an asymmetric behavior: They do not have the same reflectivity depending on which side they are lighted.…”