Optical pickup apparatus

An optical pickup apparatus, comprising:

• a first light source for emitting a first laser beam having a first wavelength;
• a second light source for emitting a second laser beam having a second wavelength that is longer than the first wavelength of said first laser beam;
• a first grating having a diffraction grating formed with a first predetermined grating pitch, for passing through said first laser beam as a main-beam, and for outputting two sub-beams composed from diffracted lights of said first laser beam;
• a second grating having a diffraction grating formed with a second predetermined grating pitch different from said first predetermined grating pitch, for passing through said second laser beam as a main-beam, and for outputting two sub-beams composed from diffracted lights of said second laser beam;
• and
• an optical system for guiding the main beam and the two sub-beams to a recording surface of a recording medium, and for guiding the main beam and the sub-beams reflected at the recording surface of said recording medium to a photodetector to form respective spots corresponding to the main-beam and the two sub-beams reflected, on light-receiving surfaces of said photodetector,
• wherein assuming that a distance from said first light source to said first grating is given by a, a distance from said second light source to said second grating is given by b, said first predetermined grating pitch is given by I, said second predetermined grating pitch is given by J, the wavelength of said first laser beam is given by λ1, and the wavelength of said second laser beam is given by λ2,
• λ1/λ2>(I·b)/(J·a)
• is satisfied.