| 摘要 |
PURPOSE:To obtain extremely uniform grating structure by setting an antireflection film provided on the rear surface of a substrate in a manner as to satisfy antireflection conditions for both of light irradiation in the stage of forming the grating pattern and light irradiation in the stage of use. CONSTITUTION:The antireflection film 30 is formed on the rear surface of the substrate 5. The substrate 5 consists of a y-cut LiNbO3 crystal and the antireflection film 30 consists of an SiO2 film (1.48 refractive index). The antireflection conditions in both the manufacturing stage and using stage hold if the coincident point of the min. values of the curves A and B is found. The min. values of the two curves near film thickness d=1.2mum (shown by an arrow) coincide with each other and such value is the value to be determined. Namely, the film thickness (d) of the antireflection film 30 is made 1.12mum. The reflected luminous flux by the antireflection film 30 is thus substantially obviated. |
