Patent ID: 7715302

Claim:
An optical element for use in an optical pickup apparatus, the optical element comprising: a substrate made of resin; and an antireflection layer transmitting a light flux with a wavelength λ1 from a first light source, arranged on at least one surface on the substrate and comprising a low refractive index layer and a high refractive index layer, wherein the resin includes a polymer with an alicyclic structure, the wavelength λ1 satisfies 350 nm≦λ1≦450 nm, the low refractive index layer has a first refractive index when the light flux with the wavelength λ1 passes through the low refractive index layer and comprises a material selected from the group consisting of silicon oxide, aluminum fluoride, yttrium fluoride, magnesium fluoride, and a mixture of silicon oxide and aluminum oxide, the high refractive index layer has a second refractive index that is higher than the first refractive index when the light flux with the wavelength λ1 passes through the high refractive index layer and comprises a material selected from the group consisting of scandium oxide, niobium oxide, lanthanum oxide, praseodymium titanate, lanthanum titanate, lanthanum aluminate, yttrium oxide, hafnium oxide, zirconium oxide, tantalum oxide, a mixture of tantalum oxide and titanium, and silicon nitride, wherein the polymer with an alicyclic structure comprises repeating units whose weight average molecular weight (Mw) is in a range of 1,000-1,000,000, the repeating units comprises an alicyclic repeating unit (a) represented by Formula (1) and a chain structure repeating unit (b) represented by Formula (2) or (3), a total content of the repeating unit (a) and the repeating unit (b) is not less than 90% by weight, a content of the repeating unit (b) is not less than 1% and less than 10% by weight, wherein, X represents an alicyclic hydrocarbon group, wherein R1 through R13 in Formulas (1), (2), and (3) each represents independently a hydrogen atom, a halogen atom, an alkoxy group, a hydroxyl group, an ether group, an ester group, a cyano group, an amido group, an imido group, a silyl group, or a chain hydrocarbon group, provided that the chain hydrocarbon group may be substituted with a polar group of a halogen atom, an alkoxy group, a hydroxyl group, an ether group, an ester group, a cyano group, an amido group, an imino group, or a silyl group, and the symbol “. . . .” in Formula (3) represents a carbon-carbon saturated bond or a carbon-carbon unsaturated bond.