| 摘要 |
PURPOSE:To make the performance stable by directing the grating side of a collimator lens toward a light source and forming the rear face as a plane having large reflectance to prevent light noise due to returned light. CONSTITUTION:The laser light of the light source 1 is condensed on a recording medium 2 via a collimator lens 3 and its reflected light is detected by a photodetector 6. The grating face 7 of the lens 3 whose cross section is sawtoothed is directed to the light source and the rear face 8 is formed as a plane having reflectance. Much quantity of the luminous flux collimated by a face 7 is reflected by the rear face, the NA of the lens 3 is selected properly to increase the returned luminous flux to the light source thereby suppressing the returned light source. Thus, the returned noise is prevented by simple structure to stabilize the performance. |
