SEMICONDUCTOR LASER DRIVING CIRCUIT

摘要

PURPOSE:To attain modulation of about 100% with less harmonic distortion by providing a constant current source adjusting a DC component included in a signal current subjected to high-speed switching to reduce a modal noise with simple constitution. CONSTITUTION:A picture signal from a terminal 1 of a semiconductor laser driving circuit is applied to a base of a transistor (TR)4, which converts the signal into a signal current modulating a semiconductor laser 8 by using a resistor 5. A bias current from a constant current source 9 for bias is supplied to the said laser 8 and the signal current modulating the laser 8 is switched by a current switching circuit comprising TR6, 7. The laser 8 is modulated by a current superimposing the signal current and a fixed bias together. A constant current source 10 for absorbing a DC component is provided between a connecting point of the TR 4 and the TRs 6, 7 of the laser driving circuit and ground, a modal noise is reduced with simple constitution, about 100% of modulation is applied and harmonic distortion is reduced.