| 摘要 |
PURPOSE:To provide the defocus detection system which simplifies assembling and adjustment of an optical head. CONSTITUTION:0th-order light, +1st-order light, and -1st-order light of reflected light from a disk recording medium 8 are individually received by detectors 17a to 17c, and at least one detector 17b which receives + or -1st-order light is used as the defocus detector whose dimensions are made smaller than the incident beam diameter. The output value for maximum 23 of the information signal amplitude or the output value for detection of a scoop signal of monitor output of a semiconductor laser is stored, and this stored value is subtracted from the output value of the defocus detector to cancel the offset, and the subtraction signal is used as a defocus signal. |
