| 摘要 |
PROBLEM TO BE SOLVED: To enable the use of a low-output laser and to reduce electric power consumption by improving the light utilization efficiency of an optical head of a three beam system. SOLUTION: Diffraction gratings 2 of a diffraction element 1 for branching the laser beam emitted from a laser beam source to three beams are formed as a region smaller than a luminous flux diameter in a direction corresponding to information tracks and larger than the luminous flux diameter in a direction orthogonal therewith, by which the degradation in the light utilization efficiency is suppressed. The expansion in the spot diameter of the sub-beams in the direction orthogonal with the information tracks on the optical disk relating to tracking performance is suppressed and the impairment of the tracking performance is averted by forming the diffraction grating grooves to a shape larger than the exit luminous flux diameter in the direction orthogonal with the information tracks. |
