Patent ID: 8902514

Claim:
A diffractive lens with the function of focusing light, wherein the diffractive lens has a side on which a diffraction grating is arranged on either an aspheric surface or a spherical surface in its effective area, and wherein the diffraction grating has n 0 phase steps, which are arranged concentrically around the optical axis of the diffractive lens, and wherein the radius r n of the circle formed by every n th one (where n is an integer that falls within the range of 0 through n 0 ) of the phase steps as counted from a side of the optical axis of the diffractive lens satisfies r n =√{square root over ( a {( n+c+d n )− b ( n+c+d n ) m })}{square root over ( a {( n+c+d n )− b ( n+c+d n ) m })} where a, b, c and m are constants that satisfy a>0, 0≦c<1, m>1, and 0.05 ⁢ b 0 < b < b 0 b 0 = 1 mn 0 m - 1 and d n is an arbitrary value that satisfies −0.25<d n <0.25.