Abstract: A system for the generation of modulated optical signals, wherein to the d.c. bias current of a semiconductor laser (1) associated with an opto-electronic feedback circuit (2) including a delay, there are superimposed the variations of a current obtained by detecting an optical signal resulting from the combination of an optical, amplitude-modulated input signal and of the optical signal present in the feedback circuit. By a suitable choice of the modulation frequency (f2) of the input signal and of the low-frequency gain (B) of the feedback loop (2), the laser output signal is amplitude-modulated at a frequency equal to the modulation frquency (f2) of the input signal.

Abstract: An optical beam is injected into a single-mode fiber of a given length and outgoes from an end face of the fiber, is reflected by a reflecting optical system into the fiber; the optical power of the reflected beam guided backward by the fiber is measured. The end face of the fiber is placed in the optical center of the reflecting system to obtain the maximum reflected power, and is then deviated from the position detecting the occurring reductions of the reflected optical power.