The application of Fresnel equations and anti-reflection technology to improve inclined exposure interface reflection and develop a key component needed for Blu-ray DVD–micro-mirrors**Partially based on the paper ‘Optimal fabricate technology of polymer micro optical mirror’ by Kuo-Yung Hung, Jung Chiang Liao, H P Feng, H H Tsai presented at the IEEE International Conference on Industrial Technology (IEEE ICIT2008) (Sichuan University,

Abstract

The goal of this paper is to explore the use of inclined exposure technology to fabricate millimeter-grade thick film polymer optical microstructures on glass substrates and to resolve the partial reflection of optical energy at interfaces that causes the structural problem of unnecessary photo cross-linking, which can affect the structural shape. This paper uses inclined exposure technology to cause UV illumination to impinge on the substrate at a certain non-perpendicular angle and fabricate a three-dimensional optical-grade micro-mirror as part of an effort to develop an integrated, miniature Blu-ray optical pickup head. Although a transparent glass substrate was employed in the experiment, the system included mask glass (nm = 1.53), glass substrate (ng = 1.5) and photopolymerized polymer (np = 1.67). UV light tends to undergo partial reflection at the interfaces due to the materials' different refractive indices. This optical phenomenon is particularly severe at higher exposure energies (∼14 000 mJ cm−2) in the fabrication of millimeter-grade thick films. The Fresnel equations are used to calculate that the maximum interface reflection of optical energy is approximately 1.5%. This paper therefore selects a medium with a matching refractive index (ngl = 1.473) and removable anti-reflection technology in order to resolve the interface reflection problem, and applies this solution to 45° micro-mirror manufacturing technology, enabling a surface roughness of approximately 20 nm (λ/20, λ = 405 nm) as measured by WYKO.