Patent ID: 6906991

Claim:
An optical head comprising: a light emitter/detector for emitting a laser light towards a recording surface of an optical disc having information optically recorded thereon and detecting a return light component of the laser light reflected at the recording surface of the optical disc to detect at least a tracking error signal; a diffraction grating provided between the light emitter/detector and the optical disc to split the laser light emitted from the light emitter/detector into at least three beams; a light converging optical system provided between the diffraction grating and optical disc to converge the lights split by the diffraction grating to the recording surface of the optical disc; the light emitter/detector comprising a first light source to emit a first light beam of a first wavelength and a second light source to emit a second light beam of a second wavelength which is less than said first wavelength; and the diffraction grating having formed therein a plurality of slits whose depth is predetermined so that the efficiency of diffraction of first-order light generated when the first light beam having the first wavelength is incident upon the diffraction grating is higher than that of the efficiency of diffraction of first order light generated when the second light beam having the second wavelength is incident upon the diffraction grating, wherein the depth of the slits formed in the diffraction grating is selected so that the efficiency of diffraction of first-order light when the first light beam is incident upon the diffraction grating is higher than 5% while the efficiency of diffraction of first-order light when the second light beam is incident upon the diffraction grating is lower than 5%.