| 摘要 |
Beams of light emitted from a light source 1 are incident on a polarizer 14 . In the event that the direction of a transmission axis of the polarizer 14 is adjusted in advance such that the polarizer 14 transmits P polarized light, only S polarized light can be attenuated. Beams of light which transmit through a diffracting device 2 and a collimator lens 3 for incidence on a beam splitter 4 a are made up substantially only by P polarized light. Part of the beams of light, which is reflected on the beam splitter 4 a, is incident on a photodetector 13 for use for feedback control of outputs from the light source 1 . Since S polarized light is attenuated by the polarizer 14 , only P polarized light is incident on the photodetector 13 . Consequently, even in case the quantity of emitted laser beams changes, a ratio between the quantity of light for record and reproduction and the quantity of light for APC remains substantially constant, whereby the accuracy of detecting the intensity of laser beams can be increased, thereby making it possible to avoid errors in record and reproduction.
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