Patent ID: 6760159
Filing Date: 2004-07-06
Classification: G02B,G03H

Abstract:
A diffractive optical element comprising:L diffraction gratings, L being three or more, including a first diffraction grating, a second diffraction grating, and up through an L-th diffraction grating, wherein, letting a grating thickness of said first diffraction grating be denoted by d1, a grating thickness of said second diffraction grating be denoted by d2, a grating thickness of said L-th diffraction grating be denoted by dL, a refractive index of said first diffraction grating at a wavelength &lgr; be denoted by n1(&lgr;), a refractive index of said second diffraction grating at the wavelength &lgr; be denoted by n2(&lgr;), a refractive index of said L-th diffraction grating at the wavelength &lgr; be denoted by nL(&lgr;), and a wavelength within a visible spectrum be denoted by &lgr;0, the following condition is satisfied for each of three wavelengths within the visible spectrum wherein the three wavelengths have a difference of 50 nm or larger from each other: (n1(Î»&it;â€ƒ&it;0)-1)&it;d1+&Sum;i=2i=L&it;&PlusMinus;(ni(Î»&it;â€ƒ&it;0)-1)&it;d&it;â€ƒ&it;i=Î»&it;â€ƒ&it;0,wherein for each of said second diffraction grating up through said L-th diffraction grating, Â± represents + if the respective grating thickness varies in the same direction as the grating thickness of said first diffraction grating on the basis of direction of increase or decrease of the grating thickness of said first diffraction grating, and Â± represents âˆ’ if the respective grating thickness varies in the opposite direction as the grating thickness of said first diffraction grating on the basis of direction of increase or decrease of the grating thickness of said first diffraction grating.