Patent ID: 7103285

Claim:
An optical transmitter comprising: a modulation signal source for outputting modulation signals of a predetermined frequency; a semiconductor laser source driven by said modulation signals outputted from said modulation signal source to output laser light modulated according to said modulation signals; an optical amplifier, including an erbium-doped optical fiber, for amplifying the laser light from said semiconductor laser source; a modulation depth control system for controlling a ratio of an amplitude modulation depth of amplified laser light outputted from the optical amplifier, to an amplitude modulation depth of the laser light inputted into said optical amplifier, is set in the range of 60% or less; a signal source for outputting signals to be transmitted, in the form of an electric signal; and an external modulator which is provided on a transmission line between said semiconductor laser source and said optical amplifier, which amplitude-modulates the laser light outputted from the semiconductor laser source, based on the electric signals outputted from said signal source, and which outputs the amplitude-modulated laser light as light including signals to said optical amplifier.