| 摘要 |
PURPOSE:To prevent the excessive emission of light and to increase the lifetime of an optical transmitter by inputting the two branched input signals to a laser driving circuit and a mark rate detecting circuit and inhibiting the emission of the laser light when the output of the mark rate detecting circuit is smaller than the prescribed value A or larger than the prescribed value B respectively. CONSTITUTION:The signal inputted to an input terminal 12 is branched into two signals and inputted to a semiconductor laser driving circuit 1 and a mark rate detecting circuit 4. Then the input signal is cut off, and the output value of the circuit 4 serving as an excessive DC signal higher than the high level of a no-input start signal or a prescribed input signal is smaller than the prescribed value A or larger than the prescribed value B. As a result, a cut-off circuit 3 works to cut off the supply of the driving current to a semiconductor laser 6 from the circuit 1. Then the light emission of the laser 6 is stopped. Thus the excessive emission of light is prevented and the lifetime is increased for the laser 6. |
