| 摘要 |
<p>Semiconductor lasers (101a-101c) project beams having wavelengths of approximately 400nm, 650nm and 780nm, respectively. A transmittance adjusting element (114) is arranged on an optical path for passing reflection light from a disc (111). The transmittance adjusting element (114) is provided with a first optical thin film (141) for relatively changing transmittance of the beam having a wavelength of 650nm to the transmittances of the beams having wavelengths of 400nm and 780nm, and a second optical thin film (141) for relatively changing the transmittance of the beam having a wavelength of 780nm to the transmittances of the beams having wavelengths of 400nm and 650nm. The transmittance adjusting element (114) has a function of making the quantity of light entering a photodetector (115) the same, irrespective of the type of the medium.</p> |
