Patent ID: 7672050

Claim:
A refractive index controlled diffractive optical element having two-dimensional refractive index distribution to be written on a transparent material, wherein a first refractive index region with a refractive index n 1 and width d 1 is formed in said transparent material, and ith refractive index region with a refractive index n i where n i ≠n i−1 and a width d i is formed adjacent to the (i−1)th refractive index region on the opposite side of (i−2)th refractive index region across the (i−1)th refractive index region in the case of i is larger than 2, and on the arbitrary side of (i−1)th refractive index region in the case of i is equal to 2, where i is an integer within a range of 2≦i≦x, and where x is an integer not less than 3 and x is the maximum number of the refractive index region.