| 摘要 |
PROBLEM TO BE SOLVED: To reduce the variation of sizes of light spots on a photodetector. SOLUTION: The variation of sizes of light spots 14 is reduced by arranging optical elements 18a, 18b controlling the focul position of light beam 8 between an optical system 4, 6 and a photodetector 12 having bisected light receiving surfaces 12a, 12b, and by controlling the size of the light spot 14 on the photodetector 12 to obtain an appropriate size in accordance with optical characteristics of the optical elements 18a, 18b. |
