| 摘要 |
PURPOSE:To enable detection of contamination of objective lens to be carried out without requiring any dedicated reference disc. CONSTITUTION:A comparator 36 compares an output Vp from an LPF 35 with a reference level signal Vref and delivers an output to a controller 37. Specific region of a disc 30 is subjected to recording and reproduction for every frame under control of the controller 37. At the time of recording, a laser diode 31 is driven intermittently by a recording pulse, having a predetermined period and a phase being shifted as the recording times increases, generated from a pulse generator 38. Writing position in the specific region of the write once disc 30 is shifted sequentially every time when the recording times increases thus prolonging the high level interval of reproduced signal and recording/ reproducing operation is stopped when Vp > Vref is satisfied. Since the specific region of the disc 7 has a predetermined reflectance (target value), contamination of objective lens can be detected by detecting the level of light reflected on the specific region. |
