| 摘要 |
PROBLEM TO BE SOLVED: To prevent the sensitivity of a focus error signal from lowering due to a large spot diameter since a focus is deviated due to the positional deviation of an object lens. SOLUTION: The focus error signal is detected by using luminous flux in which the wave aberration of one of the luminous flux of a +1st order light beam and the luminous flux of a -1st order light beam for focus error signal detection is smaller than that of the other of the luminous flux of the +1st order light beam and the luminous flux of the -1st order light beam, and wave aberration is small. |
