Patent ID: 7688512
Filing Date: 2010-03-30
Classification: G01J,G02B

Abstract:
1. A transmissive diffraction grating comprising a substrate and a plurality of ridges provided parallel to one another at constant periodicity p on the substrate, wherein the ridges include a first layer, a second layer, and a third layer with non-continuous refractive indices arranged in that order from the substrate outward, the first layer adjacent the substrate, in terms of its refractive index, exhibits a difference of 0.1 or less relative to the substrate, the second layer has a higher refractive index than the first layer and third layer and satisfies the following conditions (A) to (C): (A) the refractive index n (B) for a single ridge, a cross-sectional area S of a cross-section of the second layer perpendicular to the longitudinal direction of said ridge is in the range of 0.75p (C) a thickness d