Patent ID: 7463430
Filing Date: 2008-12-09
Classification: G02B,G11B

Abstract:
1. A design method for designing a diffraction element including a first and second layer attached to one another and a diffraction pattern in which each of step-like protruding portions located at predetermined intervals between the first and second layers includes s steps wherein the first and second layers are respectively made from a first and second material through which a first, second and third wavelength λ 1 , λ 2 and λ 3 of an optical beam passes, the design method comprising a selection step of selecting the first material and the second material such that the first material's refraction indexes n wherein i=1,2,3 j=1,2,3 and i≠j; δi=n “ρij” represents a ratio of wavelengths or “p1”, “p2” and “q3” represents any whole numbers; “εi” represents a difference from whole numbers or and “gcd(a,b)” represents the greatest common divisor of whole numbers a and b or wherein “q2” represents any whole numbers.