| 摘要 |
PURPOSE:To facilitate coping with a burst signal by a method wherein the output of a regulating means is changed so as to make the level of a bias current lower than the threshold level of a light emitting device when no signal is inputted into a 2nd transistor. CONSTITUTION:In a no-signal state, an RTS (Request To Send) signal given to the positive phase sequence input of the gate lC3 of an ECL (Emitter Coupled Logic) is at a low level and hence the output of the gate IC3 is also at a low level and given to the positive phase sequence input of an operational amplifier IC2 constituting a reverse amplifying circuit. On the other hand, in the no-signal state, a semiconductor laser LD is in an extinguished state and hence a monitor current is not applied to a photodiode PD. Therefore, the output of the operational amplifier IC2 is fixed at a low level. Then, if the value of a resistor R9 is properly selected, a bias current in this state can be fixed at the value lower than the threshold current of the semiconductor laser LD so that the light emission of the semiconductor laser LD in the no-signal state can be avoided. With this constitution, a burst signal can be coped with. |
