Patent ID: 7986605

Claim:
An optical pickup comprising: a light source emitting a light beam; an objective lens condensing the light beam emitted from the light source onto an optical disc; at least one divergent angle conversion lens disposed between the light source and the objective lens and changing a divergent angle of the light beam; driving means for driving the at least one divergent angle conversion lens in a direction of an optical axis; an optical detection device detecting a return light beam reflected at the optical disc; and an environmental change detecting unit configured to detect change in environmental temperature, wherein the objective lens is made of a refractive element having, on one surface thereof, a diffraction structure in a stepped shape or a blazed sectional shape, which generates diffraction light providing a spot adapted to perform satisfactory recording and/or reproducing, the objective lens satisfying a relationship of 2.5×10 −3 ≦ΔWFA/(ΔT×f)≦2.6×10 −3 when first-order light is used, a relationship of 1.8×10 −3 ≦ΔWFA/(ΔT×f)≦2.6×10 −3 when second-order light is used, a relationship of 1.1×10 −3 ≦ΔWFA/(ΔT×f)≦2.6×10 −3 when third-order light is used, a relationship of 0.7×10 −3 ≦ΔWFA/(ΔT×f)≦2.6×10 −3 when fourth-order light is used, and a relationship of 0.2×10 −3 ≦ΔWFA/(ΔT×f)≦2.6×10 −3 when fifth-order light is used (ΔWFA denotes an amount of wavefront aberration of the objective lens corresponding to change in environmental temperature, ΔT denotes an amount of the change in environmental temperature, and f denotes a focal length of the objective lens), and wherein the at least one divergent angle conversion lens is driven step by step in accordance with a detection result of the environmental change detecting unit.