Patent ID: 7688701

Claim:
An objective optical system for use in an optical pickup apparatus for recording or reproducing information on an information recording surface of a first optical information recording medium with a protective layer with a thickness t 1 using a first light flux with a wavelength λ 1 emitted from a first light source, the objective optical system comprising: a first lens with a positive refractive power comprising plastic; a second lens with a positive refractive power comprising plastic and arranged in a closer position to the first optical information recording medium than the first lens; and a first phase structure arranged on one of optical surfaces of the first lens and the second lens, wherein when a wavelength of the first light flux changes +5 nm from the wavelength λ 1 , a wavefront aberration change amount of the objective optical system on the information recording surface of the first optical information recording medium satisfies 0.031 λ 1 rms or more, and 0.095 λ 1 rms or less, and when an ambient temperature of the objective optical system changes +30° C. from a design reference temperature, the wavefront aberration change amount of the objective optical system on the information recording surface of the first optical information recording medium satisfies 0.010 λ 1 rms or more, and 0.050 λ 1 rms or less.