| 摘要 |
PURPOSE:To eliminate stray light and to detect a signal of a high quality by providing a light absorbing plate of a prescribed shape on the inside of an optical block for supporting an optical element group and also preventing an invasion of external light. CONSTITUTION:A light absorbing plate 10 whose photodetecting surface is like a saw tooth, and to which a black painting is performed is provided on the inside of an optical block 9. Light emitted from a semiconductor laser 1 is condensed onto a recording medium 5 through a collimating lens 2, a half mirror 3 and an objective 4. Its reflected light goes backward, is reflected by the half mirror 3, and condensed to a photodetector 8 by a convex lens 7. A part of light which is made incident to the half mirror 3 from the semiconductor laser 1 is reflected by the half mirror 3 and made incident to the light absorbing plate 10, and only light Io reflected three times by the saw tooth-like surfaces A, B goes backward and is made incident to the photodetector 8, but its intensity is weakened to about 1/1000 of incident light Ii to the light absorbing plate 10, therefore, a signal of a high quality is detected. |
