A process for delaying a useful optical signal (P1) having a wavelength value λ between 0.2 μm and 3 μm, with respect to a reference optical signal (P2) having the same wavelength value λ. The process includes having the useful optical signal propagate along a tapered fiber portion. A length of the tapered fiber portion can be varied using stretching means that are light, less cumbersome and less expensive compared to those necessary for a standard optical fiber. In addition, the delay value which is effective for the useful optical signal can be varied over a wide range. Such process can be useful for interferometry measurements in particular.