| 摘要 |
PURPOSE:To facilitate the adjustment in a laser element drive by setting a voltage of one signal which is inputted to a non-inverting terminal of a comparator by bringing the DC bias current transmitted by the drive unit into coincidence with the value at the modulation high level time. CONSTITUTION:Modulation level signals 0, 1 from a modulator 4 are fed in response to the presence or absence of modulation to the non-inverting input terminal of a comparator 5, divided by a variable resistor VR2 and a resistor R and injected. The comparator 5 produces a compared difference output of the detection signal from the detector 3 to the drive unit 2 with the injected input as a control signal. When the modulation input a is high level and the modulation level signal is 0, the set values of the resistors VR2 and the resistor R can be ignored. Then, the modulation input is as low level and the modulation level signal is as 1. Here, the signal 1 is set by the resistor VR2 so that the DC bias current obtained when the DC bias current of the drive unit 3 is high level becomes coincident to the DC bias current value at the modulation signal current superposing time. In this manner, the setting of the resistor VR2 does not exert the influence to the adjustment at the high level time. |
