Abstract: An equipment for measuring length or refractive index of a dielectric element capable of transmitting optical frequency signals, for instance an optical wave guide. The used method consists in making at least one measurement of the propagation time of a light impulse over a length of the said element, and deducing therefrom the unknown length or index, if one of the latter is previously known. The equipment includes an injector of light signals, a separator dividing each light pulse signal into a delayed and a non-delayed one respectively transmitted through a first and a second path one of which contains the dielectric element to be measured and the other of which is used as a comparison one, a detector at the output of each of said paths, and a viewing element displaying the outputs of both detectors on a common screen, for instance that of an oscilloscope whereby the propagation time difference between said paths is translated into the spacing between the said outputs observed on said screen.

Abstract: A method essentially consisting in measuring the duration of the go and return travel of a light impulse between an accessible end of an optical cable and a break in the said cable. The distance of the break from the latter end can be calculated if the refractive index of the light conducting material is known. The equipment essentially comprises a source of light impulses forming optical signals, an injector element coupling the source to the cable, a separator dividing each optical signal into two signals respectively traveling on a first and a second path, the latter of which includes the above-mentioned go and return travel, detector elements detecting the signals at the outputs of their paths, and a viewing element displaying the detector outputs on a common screen.