Semiconductor light source for an optical transmitter and an optical transmission module using the semiconductor light source

#1. Field of the Invention

#The present invention relates to a semiconductor light source for an optical transmitter and an optical transmission module using the above semiconductor light source.

#2. Description of the Related Art

#In the drawings:

#FIG. 1 is an explanatory view for explaining a conventional drive method of a semiconductor laser;

#FIG. 2 is a basic drive circuit of a semiconductor laser having a differential type;

#Before describing the preferred embodiments, a conventional art and its problem will be explained in detail hereinafter.

#FIG. 1 is an explanatory view for explaining a conventional drive method of a semiconductor laser. In FIG. 1, the ordinate shows an intensity of an optical output, and the abscissa shows current flowing through the semiconductor laser. As shown in FIG. 1, when the current increases gradually, the intensity of the optical output increases slightly. Further, when the current exceeds a particular value shown by "Ith", the optical output of the semiconductor laser considerably increases, and the semiconductor laser starts laser oscillation. In general, this particular value Ith is called "oscillation threshold current".

#In above mentioned drive method, the current flowing through the semiconductor laser is divided into two components, i.e., bias current component IB which appears to be direct current (DC) component and modulation current component Imod. In the conventional drive method, since the bias current component IB is set to the vicinity of the particular value Ith, either the large optical output or the small optical output is generated in accordance with the modulation current. That is, when the modulation current is smaller than the particular value Ith, the optical output becomes small. When the modulation current is larger than the particular value Ith, the optical output becomes large. In general, the large optical output is used as a digital signal "1", and the small optical output is used as the digital "0".