| 摘要 |
A hybrid objective lens has a refractive lens and a diffractive optical element constructed by plural coaxial ring-shaped zones on at least one optical surface thereof. When n1, n2 and n3 each is a diffraction order of a diffracted ray having a maximum light amount among diffracted rays of each of first, second and third light flux having wavelength »1, »2 and »3 when respective light flux comes to be incident into the diffractive structure respectively, the following formulas are satisfied:
€ƒ€ƒ€ƒ |n1| > |n2|, and |n1| > |n3|, and
€ƒ€ƒ€ƒ the hybrid objective lens converges a n1-th, n2-th and n3-th order diffracted ray of the first, second and third light flux onto an information recording plane of each of the first, second ant third optical information recording medium respectively so as to form an appropriate wavefront within respective prescribed necessary image side numerical apertures. |
