Optical disc device

An optical disc device that records and/or reproduces information on an optical medium in which a guide groove is formed on a signal recording layer, the optical medium being capable of recording information in both a land portion and a groove portion formed by the guide groove, the optical disc device comprising:

• a light source;
• an objective lens configured to condense a light beam radiated from the light source onto the signal recording layer formed on the optical medium;
• an objective lens moving unit configured to move the objective lens in a tracking direction;
• an optical splitting element configured to split a luminous flux of a light beam reflected by the optical medium into a plurality of regions;
• a light detecting unit configured to receive each of light beams corresponding to the plurality of regions split by the optical splitting element and generate a light reception signal;
• a control signal generating unit configured to generate a tracking error signal indicating a deviation amount between a condensing spot on the signal recording layer and the guide groove in the tracking direction on the basis of a signal from the light detecting unit;
• and
• a servo control unit configured to move the objective lens in the tracking direction via the objective lens moving unit on the basis of the tracking error signal generated by the control signal generating unit and cause the objective lens to move and track on a desired land portion or groove portion,
• wherein a weighting of a second region among the plurality of regions is larger than a weighting of a first region,
• a weighting of a fourth region is larger than a weighting of a third region, and
• when a groove pitch of the guide groove is represented as Gp, a wavelength of the light beam radiated from the light source is represented as λ, and a numerical aperture of the objective lens is represented as NA, and
• a radial direction is represented as an x axis, and a tangential direction is represented as a y axis with a returning luminous flux serving as a unit circle having a radius of 1, and a center of a position on the returning luminous flux serving as an origin,
• the first region is a region including
• (x,y)=(+k/2,0) [Math. 1]
• expressed using k=λ(NA·Gp),
• in other words, the first region is a region including a center of a region in which 0th-order light and +1st-order light diffracted by the guide groove overlap,
• the second region is a region including one or both of
• (x,y)=(+k/2,+√{square root over ((8−3k2)/12)}) [Math. 2]
• and
• (x,y)=(+k/2,−√{square root over ((8−3k2)/12)}) [Math. 3]
• the third region is a region including
• (x,y)=(−k/2,0) [Math. 4]
• in other words, the third region is a region including a center of a region in which the 0th-order light and −1st-order light diffracted by the guide groove overlap, and
• the fourth region is a region including one or both of
• (x,y)=(−k/2,+√{square root over ((8−3k2)/12)}) [Math. 5]
• and
• (x,y)=(−k/2,−√{square root over ((8−3k2)/12)}). [Math. 6]