| 摘要 |
PURPOSE:To automatically control the respective light quantities of two semiconductor lasers by obtaining discretely respective light emitting quantities to the same chip through a photodetector, which can monitor only the summed light quantity structurally, by turning off one of two semiconductors at the time when it is unnecessary. CONSTITUTION:A switching circuit 3 controlled so as to turn off when a preformat part 7, previously provided for storing address information in every sector of a track on a recording medium 6, is read out, and to turn on when a data area 8 other than the above-mentioned one is read out. As the result, when the switching circuit 3 is turned off, a light quantity (a), corresponding to a laser element LDa, is inputted to an operation circuit 4, and when it is turned on, the light quantity a+b, corresponding to the sum of the LDa and the LDb, is inputted to the circuit 4. Accordingly, if respective input values are inputted to the arithmetic circuit 4 temporarily, and a difference of them is taken, individual light quantities a, b are easily obtained, and an automatic light quantity control can be independently applied to the LDa and the LDb. |
