Patent ID: 7319655

Claim:
A diffractive optical element, comprising: an optical surface having a first diffractive structure to generate n 11 -th order diffracted ray when a first light flux having a wavelength λ1 (nm) comes in and to generate n 21 -th order diffracted ray (n 11 .≧n 21 ) when a second light flux having a wavelength λ2 (nm) (λ2>λ1) comes in; and an optical surface having a second diffractive structure to generate n 12 -th order diffracted ray when the first light flux having the wavelength λ1 (nm) comes in and to generate n 22 -th order diffracted ray (n 12 .≧n 22 ) when the second light flux having the wavelength λ2 (nm) (λ2>λ1) comes in; wherein the diffractive optical element satisfies the following formula (1): δφ A12 ≠δφ B12 (1) where, δφ A12 ={n 11 ·λ 1 /( N 11 −1)}/{ n 21 ·λ 2 /( N 21 −1)} (2) δφ B12 ={n 12 ·λ 1 /( N 12 −1)}/{ n 22 ·λ 2 /( N 22 −1)} (3) N 11 , N 21 are refractive index of the first diffractive structure respectively for the wavelength of λ 1 and λ 2 , and N 12 , N 22 are refractive index of the second diffractive structure respectively for the wavelength of λ 1 and λ 2 .