| 摘要 |
PURPOSE:To acquire constant optical output while keeping high speed operation characteristics at the time of signal input, by providing a circuit to detect whether a signal is on or off based on integrated output of an electric input signal, and a switch to stop the supply of bias current to a semiconductor laser in the case of the absence of an signal based on a detection signal. CONSTITUTION:A burst signal having a waveform a is input as an electric input signal SD into a waveform shaping circuit 1 of a laser driving circuit and a positive phase output signal having a waveform b is output. This signal is integrated by a detection circuit 4 composed of a resistance R1 and a capacitor C1 and is input into a waveform shaping circuit 5 to be compared with a reference voltage set at a specified value. The a positive phase output signal having a waveform d is output from the circuit 5. A transistor Tr Q11 turns on only when the output signal is at a high level and the current from a current source 2 is supplied to a semiconductor laser LD as a bias current. When the output is at a low level, the Tr Q11 turns off to cut off the current flowing through a laser LD. In this way, high speed operation characteristics of signal input can be maintained. |
