Abstract: An interferometric system for sensing and locating reflective defects in light-conducting structures comprises a mono-mode laser source (6), an incoherent source (4) with substantially the same central wavelength as the laser source, first and second couplers (10, 20) connected to the sources and to light sensors (52, 54), a first support (36) movable in one direction (D) and connected to the ends of the first and second couplers, a second support (38) oscillating in the same direction (D), reflectors (42, 43) attached to the second support opposite the ends of the first and second couplers. A third support support (40) is movable in the same direction (D) and connected to one end of the second coupler (20), a further stationary reflector (48) opposite said end, of the second coupler. The first coupler is connected to an optical waveguide (2), and devices (56, 58) for locating reflective defects in the waveguide.