The invention relates to a system for producing a signal having a variably adjustable time position or phase position, comprising at least one light source for producing a first light component (2) having a first wavelength and a second light component (2′) having a second wavelength deviating from the first wavelength and a phase modulator (5) for varying a phase of the first light component (2), wherein the system is designed to produce a beat note signal by superposing the two light components (2, 2′) and has a common optical fiber (4) for coupling in both light components (2, 2′), wherein furthermore the phase modulator (5) is arranged at an end or in the course of said optical fiber (4) and is transparent to both light components (2, 2′) and is designed to vary the phase of the first light component (2) selectively independently of a phase of the second light component (2′) or more intensely than the phase of the second light component (2′). The invention further relates to a use of such a system.