Photodetector, diffraction grating, optical pickup and optical disc apparatus

A photodetector comprising:

• a first light receiving area to receive a light beam emitted from a laser light source of a first wavelength and split by first and second diffraction gratings;
• and
• a second light receiving area to receive a light beam emitted from a laser light source of a second wavelength longer than said first wavelength and split by the first and second diffraction gratings;
• wherein said first light receiving area is disposed at a position where, when the light beam is emitted from said laser light source of the first wavelength, the light beam split by said first diffraction grating enters the first light receiving area and the light beam split by said second diffraction grating does not enter the first light receiving area, and
• wherein said second light receiving area is disposed at a position where, when the light beam is emitted from said laser light source of the second wavelength, the light beam split by said first diffraction grating does not enter the second light receiving area and the light beam split by said second diffraction grating enters the second light receiving area.