Patent ID: 7663985

Claim:
An information recording and reproduction method including the steps of: focusing light to which a spherical aberration has been added with an objective lens, and irradiating an information recording medium having a spiral-shaped or concentric recording track; converting the light reflected on said information recording medium into an electronic signal; generating a readout signal, tracking error signal, and focus error signal from said electronic signal; and controlling the position of said objective lens based on said tracking error signal and focus error signal, said method comprising the steps of: determining a focus offset of the focus error signal when the jitter of said readout signal reaches a minimum, and storing the focus offset in a memory; reading said stored focus offset from said memory; and adjusting said spherical aberration so that said tracking error signal amplitude reaches a maximum, while controlling the position of said objective lens using the focus error signal to which said read focus offset has been added; adjusting said spherical aberration so that said readout signal jitter reaches a minimum, while controlling the position of said objective lens using the focus error signal to which said read focus offset has been added; and adjusting said focus offset so that said readout signal jitter reaches a minimum, while maintaining said adjusted spherical aberration; determining the difference between said spherical aberration when said readout signal jitter reaches a minimum and said spherical aberration when said tracking error signal amplitude reaches a maximum, and storing said difference, while controlling the position of said objective lens using the focus error signal to which the focus offset when said readout signal jitter reaches a minimum has been added; reading said stored difference; and altering said spherical aberration by the amount of said difference multiplied by a constant α (0≦α≦1).