| 摘要 |
PURPOSE:To prevent a tracking error signal from being leaked to a focus error signal and to easily adjust a focus error detection system by shaping the cross section of luminous flux which is splitted to two in order to detect a focus error by a double knife edge method to be the shape of a fan with the aid of a light shielding plate. CONSTITUTION:The light shielding plate 1 is a square having a side whose length is longer than the diameter of the beam of return light D and divided to a light transmitting area and a light shielding area by a diagonal line. The part of the return light D symmetrically including one part of (+) and (-) 1st-order diffracted light component C with the zero-order diffracted light component B of a circular beam as a center is made incident on the transmitting area and the part mainly consisting of the component C is made incident on the light shielding area. Thus, the leakage of the tracking error signal to the focus error signal is reduced and the focus error detection system is easily adjusted. |
