Abstract: A multi-stage optical amplifier for a fiber-optic transmission system, in particular, an amplifier having a multi-stage configuration that allows an optimization of its performance with respect to noise, gain and bandwidth. The multi-stage amplifier has a first amplifying stage including a rare-earth doped optical active fiber; a second amplifying stage connected to the first amplifying stage, the second amplifying stage including a tellurite-based active fiber doped with a rare earth element; and a third amplifying stage connected with the second amplifying stage, the third amplifying stage including a silica-based fiber.

Abstract: A train of rectangular pulses is sent into a fiber, which pulses have such a wavelength that fiber operates under anomalous dispersion conditions, such a peak power as to cause modulation instability in the fiber and such a ratio between duration and repetition period that the average power is lower than the threshold at which stimulated Brillouin effect takes place. The maximum value of instability gain is measured in the spectrum of the pulses exiting the fiber and the Kerr non linearity coefficient is obtained from the maximum measured value of modulation instability gain by minimizing the error, in the range of power values used for the measurement, with respect to a theoretical curve expressing such maximum gain as a function of the peak power. The device to realize the method is also provided.

Abstract: To intercept and measure radiant energy back-scattered from the entrance end of an optical fiber irradiated by a pulsed laser beam, a semitransparent mirror is interposed between the irradiated fiber and a first lens assembly focusing the laser beam upon its entrance end while a second lens assembly directs reflected light rays toward a photodetector feeding an electronic processor. An extremity of the fiber including its entrance end is received in a chamber with light-absorbing walls filled with a liquid of substantially the same refractive index as the fiber; the mirror may be disposed either in front of the chamber entrance or in its interior.