Generally, optical multilayer coatings are formed on the optical surface for the purpose of anti-reflection. However, these coatings have problems of environmental resistance such that cracks or peelings.

Lately, a technique for realizing an anti-reflection function by forming a sub-wavelength scale structure on the optical surface has been widely studied [1] [2] [3] [4] [5] [6]. Such a structure is called ARS, Anti-Reflective Structure. ARS has excellent environmental resistance compared to multilayer coatings and has the advantage of low dependence on the incidence angle in terms of optical characteristics.