| 摘要 |
PROBLEM TO BE SOLVED: To generate a minute light beam spot having a deep focusing depth by specifying the relationship between the reduction rate of the light beam spot diameter and the reduction of the sidelobe light intensity distribution. SOLUTION: This device is provided with a laser light source 1, an optical element 5 which converges laser light beams on an optical recording medium 6, a photodetector 8 which detects the light signals that are modulated and reflected by the medium 6, and a phase changing means 4. The means 4 is arranged on an optical axis 90 of the laser light source 1 and the optical recording medium surface 6, and the phases of traveling wave surfaces of laser light beams 1a, 1b and 1c are changed to ring band shaped regions 4a, 4b and 4c centered around the central axis of the luminous flux cross section of the laser light beams. In the regions 4a, 4b and 4c, let r1 be the radius of the inner periphery of the ring band, r2 be the radius of the outer periphery of the ring band and R be the radius of the luminous flux cross section of the laser light beams. Then, select the ratio between the width of the ring band shaped region and the radius R, i.e., ((r2-r1)/R) to be less than in the range of 0.5. |
