Patent ID: 7692855

Claim:
An optical article having anti-reflection properties comprising a substrate having at least one main face coated with a multi-layer anti-reflection coating comprising a stack of at least one high refractive index layer and at least one low refractive index layer, wherein: each low refractive index layer has a refractive index of 1.55 or less; each high refractive index layer has a refractive index higher than 1.55 and does not comprise niobium pentoxide (Nb 2 O 5 ); said coated main face of the optical article has a mean luminous reflection factor Rv ≦1%; and: (a) the low refractive index layers of the anti-reflection coating below the outermost layer of said coating each have a physical thickness <100 nm, the ratio R T = sum ⁢ ⁢ of ⁢ ⁢ the ⁢ ⁢ physical ⁢ ⁢ thicknesses ⁢ ⁢ of ⁢ ⁢ the low ⁢ ⁢ refractive ⁢ ⁢ index ⁢ ⁢ layers ⁢ ⁢ of ⁢ ⁢ the ⁢ anti ⁢ - ⁢ reflection ⁢ ⁢ coating sum ⁢ ⁢ of ⁢ ⁢ the ⁢ ⁢ physical ⁢ ⁢ thicknesses ⁢ ⁢ of ⁢ ⁢ the high ⁢ ⁢ refractive ⁢ ⁢ index ⁢ ⁢ layers ⁢ ⁢ of ⁢ ⁢ the ⁢ anti ⁢ - ⁢ reflection ⁢ ⁢ coating is higher than 2.1, and the anti-reflection coating does not comprise a sub-layer comprising niobium (Nb); or (b) the anti-reflection coating comprises: at least one low refractive index layer having a physical thickness ≧100 nm which is not the outermost layer of the anti-reflection coating; and at least one high refractive index layer and at least one low refractive index layer, which are located above the low refractive index layer having a physical thickness ≧100 nm and not being the outermost layer of the anti-reflection coating which is the furthest from the substrate, and the ratio R T = sum ⁢ ⁢ of ⁢ ⁢ the ⁢ ⁢ physical ⁢ ⁢ thicknesses ⁢ ⁢ of ⁢ ⁢ the low ⁢ ⁢ refractive ⁢ ⁢ index ⁢ ⁢ layers ⁢ ⁢ of ⁢ ⁢ the ⁢ anti ⁢ - ⁢ reflection ⁢ ⁢ coating sum ⁢ ⁢ of ⁢ ⁢ the ⁢ ⁢ physical ⁢ ⁢ thicknesses ⁢ ⁢ of ⁢ ⁢ the high ⁢ ⁢ refractive ⁢ ⁢ index ⁢ ⁢ layers ⁢ ⁢ of ⁢ ⁢ the ⁢ anti ⁢ - ⁢ reflection ⁢ ⁢ coating is higher than 2.1, with the proviso that the layers of the anti-reflection coating taken into account for the calculation of said ratio RT are only the layers located above the low refractive index layer having a physical thickness ≧100 nm and not being the outermost layer of the anti-reflection coating which is the furthest from the substrate.