'interferenzoptisch' is an adverb here and modifies 'entspiegelt'. It means that the glass has an anti-reflective coating that works on the principle of optical interference. In other words, the coating has two partially reflective surfaces, and the coating thickness is such that light waves reflected from these two surfaces are 180 degrees out of phase at the external surface and thus cancel each other out.

You could also say 'protective glass with an optical-interference anti-reflective coating'.


refs:

Glass article with anti-reflective coating - Patent 6838178
(d) an anti-reflective coating of a metal oxide applied over said coating of ... of visible reflection is achieved by the principle of optical interference. ...
www.freepatentsonline.com/6838178.html

[PDF] CONTURAN
with optical interference coatings bet-. ween 50 nm and 100 nm thick ... Blue-violet anti-reflective coating. Green anti-reflective coating ...
www.schott.com/architecture/ english/download/conturan_e.pdf