Nonlinear frequency chirps from a stabilized injected phase-modulated fiber laser loop

Abstract

A phase-modulated frequency-shifting loop is injected by a single-frequency laser at 1.5 μm. In so-called Talbot conditions, i.e., when the modulation frequency is an integer multiple of the inverse of the cavity round-trip time, the loop generates a frequency comb whose temporal trace consists in a train of pulse doublets whose positions in time depend on the frequency of the injection laser. When the modulation frequency is slightly detuned from the Talbot condition, nonlinear frequency chirps are predicted and observed in the output pulse train. We demonstrate that these nonlinear chirps are not restricted to sinusoidal shapes, and also that the loop can be stabilized by exploiting the intracavity phase modulation.