The invention relates to a an optical recording/reproducing apparatus having a laser diode driver and, more particularly, to a technique effective for use in a magneto-optical recording and reproducing apparatus of a light modulating type.
With respect to a rewritable optical disk, reference may be made to "Nikkei Electronics", Nikkei McGraw-Hill, Inc., No. 440, pages 115-142, Feb. 8, 1988. In a light modulation type disk, among such rewritable optical disks, a temperature of a recording layer of the disk is raised to a temperature near a Curie temperature by heat of a laser beam and "1" and "0" are recorded (written) on a recording magnetic medium in terms of the direction of an auxiliary magnetic field. To read out data recorded on the optical disk, use is made of the Kerr effect such that when the laser beam is reflected from the disk surface, a plane of polarization is rotated and changed depending on a direction of the magnetization of the disk.
In the magneto-optical disk recording and reproducing apparatus of the light modulation type, it is necessary to raise the temperature of the recording layer of the disk to a temperature near the Curie temperature as mentioned above. Since the magneto-optical disk rotates at a constant speed, relative moving speeds of a laser beam spot on inner side tracks and outer side tracks differ. Namely, since the relative moving speed of the beam spot is high for the outer side tracks of the disk, it is necessary to enhance the laser beam power in order to raise the temperature of the recording layer to the Curie temperature. On the other hand, since the relative moving speed of the beam spot is low for the inner side tracks, it is sufficient to set a laser beam for raising the temperature of the recording layer to the Curie temperature to rather a weak power. For this purpose, it will be necessary to accurately control a drive current of the laser diode in accordance with track address information of the disk.
A technique is disclosed in JP-A-53-61984 (laid-open on Jun. 2, 1978) in which a drive current of a light emitting device is controlled by supplying a current from a second current source to a first current source for supplying a drive current to a light emitting diode.
USPTO Backgrounds
USPTO Backgrounds