| 摘要 |
PURPOSE:To improve the recording density by arranging an optical system forming a recording/reproduction beam spot having a diameter smaller than the track width and an optical system forming a tracking beam spot having a diameter larger than the track width into a single optical system so as to perform accurate tracking control. CONSTITUTION:A recessed track T1 and a projected track T2 are formed alternately in spiral or concentricly along the circumferential direction in the rugged pattern having the same track width on the signal recording face of a disc D. An objective lens 17 is subject to movement control in the focus and tracking directions and traces accurately the recessed track T1 or the projected track T2 of the disc D. A beam spot S2 of a large diameter and a beam spot S1 of a small diameter are irradiated on the disc face coaxially, and the spot S2 traces accurately the recessed track T1 or the projected track T2 and the spot S1 records or reproduces to/from the center of both the tracks T1,T2. |
