Optical disk recording and readout system having read, write and coarse light beams

A self-contained, replaceable laser module for use in an optical information storage and retrieval device, said module presenting a reformed laser beam for using in reading or writing data in the optical information storage and retrieval device, said laser module comprised of:

• a base plate;
• a diode laser, said laser emitting a divergent, astigmatic, non-circular cross-sectioned light beam, said laser being fixedly attached to the base plate;
• means for collimating the light beam emitted by the diode laser, said collimating means being fixedly attached to the base plate in a position to receive the beam emitted by the diode laser;
• means for correcting the astigmatism of the light beam emitted by the diode laser, said means being fixed and positioned on the base plate to correct the astigmatism in the specific diode laser attached to the base plate, and;
• means for expanding the major or minor axis of the incident beam so as to circularize the cross-section of the beam, said means being positioned on the base plate so as to induce an in-line expansion of the beam and thereby correct the crosssection of the individual diode laser attached to the base plate, said means comprising an in-line prism beam modifier system comprised of a first prism positioned and oriented to receive the incident elliptical cross-sectioned beam and partially circularize said beam, a second prism positioned and oriented to receive the partially circularized beam from the first prism and fully circularize the beam, and a planar mirror positioned between the first and the second prism so as to receive the beam exiting from the first prism and reflect the beam into the second prism, the configuration and position of the prisms oriented such that the path of the beam upon exiting the second prism is coaxial with the path of the beam incident upon the first prism;
• wherein the prism beam modifier system further comprises said means for correcting the astigmatism of the incident beam, such that upon the beam passing through said first and second prisms at a non-normal angle, an astigmatism is introduced into the beam by said first and second prism which corrects the astigmatism of the beam emitted by the diode laser.