| 摘要 |
PURPOSE:To read an offset portion generated by a light quantity variation, etc. of a light source, to eliminate it in accordance with a light quantity variation of write, and to execute stably and exactly a light spot, by providing a constant-current circuit for subtracting a stray optical signal component from a control signal component. CONSTITUTION:A reference signal corresponding to an output of a laser light source 1 is obtained by a photodiode 1' so that a signal component by a stray light is subtracted from an output of a detector 9 by a constant-current circuit 22 by said signal. The quantity of this stray light is constant by a constitution of mechanism parts, therefore, by executing the initializing in order to eliminate an offset, the offset can be eliminated after setting. When the light quantity of the laser light source 1 is varied at the time of write and at the time of read, a current flowing to the photodiode 1' being a monitor is also varied by following said variation. By following this variation, a current quantity of the constant-current circuit 22 is also varied, therefore, an offset eliminating quantity also follows it, and a correct offset elimination is always executed.
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