An optical pickup system for regenerating information signals stored on a hologram disk including a first and second recording surfaces thereon, each of the recording surfaces having a plurality of tracks aligned in a tangential direction to the hologram disk, comprising:
- a pair of light sources for generating a first and a second light beams, each of the light beams having different wavelengths;
- a diffraction device, disposed between the first light source and the hologram disk, including an orthorhombic crystal base with the first and second diffraction elements located on the sides facing each other, the first diffraction element being provided with a plurality of diffraction grooves for dividing the light beam emitted from the light source into three beams and for transmitting the three beams onto the first and the second recording surfaces, wherein each of the diffraction grooves is parallel to a radial direction of the hologram disk, the radial direction being perpendicular to the tangential direction, the second diffraction element being provided with two sub-diffracting portions divided by a radial division line for diffracting the three beams reflected from the first recording surface to a first detector, two sub-diffracting portions having grooves of which pitches are different for diffracting the three beams in different angles;
- a beam splitter, disposed between the diffraction device and the hologram disk, provided with a reflection surface for transmitting the first light beam emitted from the first light source to the first recording surface and for reflecting the second light beam emitted from the second light source to the second recording surface, wherein the reflection surface is inclined with respect to an optical axis of the light beam reflected from each of the recording surfaces, wherein the optical axis is perpendicular to the tangential and the radial direction of the hologram disk;
- a diffraction grating, disposed between the second light source and the beam splitter, provided with a plurality of diffraction grooves, for impinging the light beam reflected from the hologram disk onto a second detector;
- an objective lens, disposed between the beam splitter and the hologram disk, for focusing each of the light beams passing through the beam splitter on each of the first and second recording surfaces and for converging each of the light beams reflected from each of the first and second recording surfaces onto the diffraction grating and the second diffraction element of the diffraction device, respectively;
- the first detector having a plurality of photoelectric cells, each of the photoelectric cells being capable of measuring a light beam intensity and generating a corresponding output in the form of a light beam intensity;
- the second detector having one photoelectric cell being capable of measuring a light beam intensity and generating a corresponding output in the form of a light beam intensity;
- and
- a signal detection unit having a first signal detection circuit and a second signal detection circuit for detecting the regenerated information signal off the second recording surface, the first signal detection circuit including an adder, and a first and a second subtractors, for converting output signals from the photoelectric cells to electrical signals and for producing a focusing error, a tracking error and a regenerated information signal off the first recording surface, wherein the first light source is used for reproducing the regenerated information signal off the first recording surface of the hologram disk, during which time the second light source is turned off, and also for detecting the tracking and focusing error signals, while the second light source is used for reproducing the regenerated information signal off the second recording surface of the hologram disk.