| 摘要 |
The bias current of a current injection-type light-emitting element is set very close to the threshold current, and to guarantee a stable optical output and high-speed initiation of the light-emitting operation. In the bias current supply circuit 12 , particularly in closed-loop circuit 20 , feedback operation of bias APC with variable bias current I<SUB>b </SUB>is performed so that monitor voltage V<SUB>M1 </SUB>comes to equal reference voltage V<SUB>A1</SUB>. With this feedback operation, the steady state of V<SUB>M1</SUB>=V<SUB>A1 </SUB>is reached, and drive current I<SUB>b </SUB>(I<SUB>ba</SUB>+I<SUB>bb</SUB>) sent to laser diode 10 converges to a constant value. After a prescribed time, S/H circuit 34 is switched to hold mode. As a result, drive current I<SUB>b </SUB>(I<SUB>ba</SUB>+I<SUB>bb</SUB>) is temporarily held to a constant value corresponding to the prescribed optical output.
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