Patent ID: 7324424

Claim:
A compatible optical pickup, comprising: an optical unit to emit a short wavelength light beam for a high density optical disc, a first long wavelength light beam for a first low density optical disc, and a second long wavelength light beam for a second low density optical disc, and to receive and detect light beams reflected by the high density optical disc and the low density optical disc; an objective lens to form a light spot on the high density optical disc and the first and second low density optical disc by focusing incident short wavelength light beam and the first and second long wavelength light beams; a diffractive device to correct chromatism according to a change in a wavelength of the short wavelength light beam by diffracting the short wavelength light beam from the optical unit; and a divergent lens to increase a working distance with respect to the first low density optical disc by refracting the first long wavelength light beam from the optical unit toward the objective lens; wherein the optical unit is an optical unit to emit the short wavelength light beam for the high density optical disc, the first long wavelength light beam having a wavelength of λ1 for the first low density optical disc, and the second long wavelength light beam having a wavelength of λ2 for the second low density optical disc, the second low density optical disc having a recording density and a thickness that are different from a recording density and a thickness of the first low density optical disc, and to receive and detect light beams reflected by the high density optical disc, the first low density optical disc, and the second low density optical disc.