Single-lens optical pick-up head for accessing a DVD disc and a CD disc by switching between two optical states

Claim 1

A single-lens optical pick-up head for use in accessing both DVD and CD discs, comprising: a laser diode for providing a first light beam having a polarization; a beam splitter for receiving the first light beam in a first direction from said laser diode, and passing therethrough, in the first direction, a portion of the first light beam as a smaller second light beam; a collimator disposed to receive and collimate the second light beam; a polarizing light converter disposed to receive the second collimated light beam and output a third light beam; a polarization controller for modulating said polarizing light converter so that the polarizing light converter selectively passes the second collimated light beam output as the third light beam, with or without converting the polarization thereof, a polarization optical device disposed to receive the third light beam from said polarizing light converter and provide a fourth light beam in a second direction different from the first direction; an objective lens, disposed to focus the fourth light beam on one of the discs which reflects the fourth beam from a surface of the disc back through said objective lens so as to provide a reflected light beam as a fifth light beam passing in a third direction opposite to the second direction, back through said polarization optical device which directs the fifth beam in a direction opposite to the first direction through said polarizing light converter, and said collimator to said beam splitter; and a photodetector, for receiving a sixth light beam from said beam splitter as a reflected part of the fifth light beam, said photodetector providing an electric output signal based thereon.