| 摘要 |
PURPOSE:To attain the detection of a tracking error of an optical beam by measuring the luminous intensity distribution of a reflected light component forming nearly the center region of a beam spot among the reflected light forming the beam spot and irradiated on a photo sensor light receiving face. CONSTITUTION:Light shield plates M1, M2 at this side of the photo sensor 8 divided into two by a dividing line X are arranged and a gap E is provided between the light shield plates M1 and M2. If the shield plates M1, M2 are not placed, a circular beam spot BS is formed on the photo sensor 8 by the reflected light, but only the reflected light passing through the gap E reaches the photo sensor 8 in this case. Thus, the beam spot part of BP1, BP2 is formed respectively on divided sensor sections 8a, 8b. Photoelectric signals S1, S2 obtained by each divided sensor section are applied to a comparator 9 and a difference signal S1-S2 is outputted. This output is a tracking error detecting signal. Then, the margin against the malfunction of a disc due to the uneven shape is expanded remarkably in this way, allowing to maintain the accurate tracking error control at all times. |
