Optical disc drive having a mechanism to reduce the noise level of a focus error signal

An optical disc drive, comprising:

• a light source that emits a light beam;
• a beam dividing element that divides the light beam emitted by the light source into a main beam and a plurality of sub-beams such that each of the plurality of sub-beams has a light amount smaller than that of the main beam;
• an objective lens that converges each of the main beam and the plurality of sub-beams onto a recording surface of an optical disc;
• an astigmatism producer that gives astigmatism to each of the main beam and the plurality of sub-beams which passed through the objective lens after reflecting from the recording surface of the optical disc;
• a signal generator that has sensors respectively provided for receiving the main beam and at least two of the plurality of sub-beams which passed through the astigmatism producer, each of the sensors comprising four sensor segments, the signal generator processing output signals of the sensors in accordance with a differential astigmatic method to generate a focus error signal;
• an optical element that adjusts, without blocking transmission of a central portion of the main beam, an intensity distribution of the main beam by causing a maximum light amount of the main beam to be positioned away from a pupil center of the main beam, a radial distance between the position of the maximum light amount of the main beam and the pupil center to be within 70% of a pupil diameter of the main beam, and an intensity of the main beam to gradually decrease from the position of the maximum light amount to a periphery of the main beam,
• wherein the main beam and each of the sub-beams are incident on the optical element, and
• the optical element comprises a diffraction structure that provides a predetermined intensity distribution to an incident beam, and is provided on a surface of the objective lens.