| 摘要 |
PROBLEM TO BE SOLVED: To nearly eliminate a stray light offset that a focus error signal has. SOLUTION: A focus error arithmetic part 122 generates a focus error signal with a focus error signal =(a+d)-(b+c). When the intensity ratio a:b:c:d of stray light is 1.2:1:1:0.9, the stray light offset is proportional to 0.1. For the purpose, the stray light quantity of a photodiode (a) is adjusted by cutting the left upper part of the photodiode (a) by a specific quantity to nearly eliminate the stray light offset. |
