Abstract: Optical coatings for curved or non-planar substrates are disclosed. Optical coatings may include AR (antireflection) coatings or absorbing (“black” optical) coatings. The optical coatings may include a nanostructure layer formed on top of a stack of one or more materials. Both the nanostructure layer and the stack may be deposited on a curved or non-planar substrate using plasma-enhanced atomic layer deposition (PEALD) to provide conformal coating of the substrate. The nanostructure layer may include a mixture of aluminum hydroxide and aluminum oxide hydroxide that is formed by placing a PEALD-deposited aluminum oxide layer in heated deionized water for a predetermined time period. The materials in the stack may be alternated to provide tuning of the optical properties in the optical coating.