| 摘要 |
PURPOSE:To prevent a signal from being kept unerased by increasing an erasure spot more than a recording/reproducing spot formed on an optical disk. CONSTITUTION:A luminous flux diameter of a collimated light 55 is D2 with respect to an aperture diameter D of a collimator lens 13 and since the relation of D>D2 exists, the spot width d2 of the erasure spot 58 in the radial direction (X direction) Of an optical disk 7 is 2.k.lambda.f/D2. The width d2 of the sot 58 in the X direction is larger than a diameter d1 of the spot 57, resulting that no signal is kept unerased. Only a reflected light 53 from a semiconductor laser 1 is converged onto a detector 11 by a detection lens 10 through a wavelength separation filter 9. A focus error signal, a tracking error signal and an information signal recorded on the optical disk 7 are detected from the detector 11. |
