Patent ID: 6055122
Filing Date: 2000-04-25
Classification: G11B

Abstract:
A magnetic recording apparatus comprising:a magnetic head assembly for writing information to a disk-shaped recording medium or reading information recorded on the recording medium;an optical unit which projects light beams through a light passage formed in the magnetic head assembly on the recording medium and receives reflected light beams reflected from the recording medium;a carriage mounted with the magnetic head assembly and the optical unit to move the magnetic head assembly and the optical unit;a controller which drives the carriage on the basis of the intensities of the reflected light beams received by the optical unit to position the magnetic head assembly at a predetermined position;said optical unit comprising:a holographic unit,a light emitting device which projects a light beam on the holographic unit, anda photodetection device which receives the reflected light beams through the holographic unit and gives signals representing the intensities of the received light beams to the controller; andsaid holographic unit comprising:an optical path consisting of a first reflecting surface and a second reflecting surface extended in parallel to the first reflecting surface and capable of making light to travel along a zigzag passage between the first and the second reflecting surface,a first optical diffracting means disposed on the optical path to produce a plurality of light beams from a light beam emitted by the light emitting device,a second optical diffracting means disposed on the optical path to deflect the light traveling along the optical path,an optical condensing means disposed on the optical path to condense the light traveling along the optical path,a first entrance/exit surface disposed at a predetermined first angle to the first reflecting surface to direct the light emitted by the light emitting device toward the first optical diffracting means, anda second entrance/exit surface disposed at a predetermined second angle to the second reflecting surface to project the plurality of light beams so that the plurality of light beams fall on a position sensing track perpendicularly to the surface of the recording medium.