Emitter (2; 130; 200) of a monochromatic optical signal, this emitter comprising: - a semiconductor laser source (10; 250) that is able to emit the optical signal at a frequency v SL, this laser source comprising at least one control input for receiving an injection current able to modify the frequency v SL and at least one output via which the optical signal is emitted, this laser source emitting the optical signal at a frequency v 0 in the absence of injection current, and - a feedback loop (20; 132; 202) able to produce an injection current that is able to decrease the linewidth of the optical signal, this feedback loop being connected, on the one hand, to the output of the laser source and, on the other hand, to the control input of the laser source in order to inject into the laser source the produced injection current, this feedback loop comprising to this end an optical filter having a transmission spectrum comprising a pass band, this pass band being bounded, in the transmission spectrum, at least on one side by a rising or falling edge (42, 48) that continuously varies over a frequency interval containing the frequency v 0, this edge containing an operating point (43, 49) that is located at a preset position along the edge and that corresponds to a frequency v b contained in the frequency interval, this optical filter being connected to the output of the laser source in order to receive the optical signal and comprising an output via which the filtered optical signal on the basis of which the injection current is produced is emitted, characterized in that: - the emitter comprises, in addition to the feedback loop (20; 132; 202), a loop for automatically controlling the frequency v b to the frequency v 0, and - the feedback loop (20; 132; 202) comprises an electrical filter (98; 154; 204) that is able to selectively attenuate, in the produced injection current, the amplitude of the frequency components generated by the automatic-control loop. - a semiconductor laser source (10; 250) that is able to emit the optical signal at a frequency v SL, this laser source comprising at least one control input for receiving an injection current able to modify the frequency v SL and at least one output via which the optical signal is emitted, this laser source emitting the optical signal at a frequency v 0 in the absence of injection current, and - a feedback loop (20; 132; 202) able to produce an injection current that is able to decrease the linewidth of the optical signal, this feedback loop being connected, on the one hand, to the output of the laser source and, on the other hand, to the control input of the laser source in order to inject into the laser source the produced injection current, this feedback loop comprising to this end an optical filter having a transmission spectrum comprising a pass band, this pass band being bounded, in the transmission spectrum, at least on one side by a rising or falling edge (42, 48) that continuously varies over a frequency interval containing the frequency v 0, this edge containing an operating point (43, 49) that is located at a preset position along the edge and that corresponds to a frequency v b contained in the frequency interval, this optical filter being connected to the output of the laser source in order to receive the optical signal and comprising an output via which the filtered optical signal on the basis of which the injection current is produced is emitted, characterized in that: - the emitter comprises, in addition to the feedback loop (20; 132; 202), a loop for automatically controlling the frequency v b to the frequency v 0, and - the feedback loop (20; 132; 202) comprises an electrical filter (98; 154; 204) that is able to selectively attenuate, in the produced injection current, the amplitude of the frequency components generated by the automatic-control loop.