Patent ID: 6157488
Filing Date: 2000-12-05
Classification: G02B

Abstract:
A diffractive optical element comprising:a first optical region made of a first optical material which is substantially transparent to light within a wavelength range to be used and has a refractive index n.sub.1 ;a second optical region made of a second optical material which is substantially transparent to said light and is different from said first optical material and has a refractive index n.sub.2 ;a third optical region made of a third optical material which is transparent to said light and is different from said second optical material and has a refractive index n.sub.3, said first, second and third optical regions being arranged to be brought into contact with each other or being arranged close to each other;a first relief pattern formed in a boundary surface between said first and second optical regions and having a first pitch distribution and a depth d.sub.1 ; anda second relief pattern formed in a boundary surface between said second and third optical regions and having a second pitch distribution which is substantially identical with said first pitch distribution of the first relief pattern and a second depth d.sub.2, said first and second relief patterns being substantially aligned in a direction of an optical axis of the diffractive optical element, wherein when a ratio of the depth of the second relief pattern to the depth of the first relief pattern is .alpha. (=d.sub.2 /d.sub.1), a wavelength of the light within the wavelength range to be used is .lambda., a shortest wavelength of the wavelength region to be used is .lambda..sub.1, and a longest wavelength of the wavelength range to be used is .lambda..sub.2, the following condition is satisfied:.vertline..DELTA.N(.lambda..sub.2).vertline.>.vertline..DELTA.N(.lambda..su b.1).vertline.>0; .lambda..sub.2 >.lambda..sub.1wherein.DELTA.N(.lambda.)={n.sub.1 (.lambda.)-n.sub.2 (.lambda.)}+.alpha.{n.sub.2 (.lambda.)-n.sub.3 (.lambda.)};andwherein said ratio .alpha. of the depth of the second relief pattern to the depth of the first relief pattern is set such that a wavelength dependency of a diffraction efficiency is reduced.