Offset-free optical frequency comb self-referencing with an f -2f interferometer

We demonstrate a self-referencing locking method for an optical frequency comb that leads to an offset-free frequency comb. It works with a standard f−2f interferometer and phase-locks the carrier–envelope offset frequency to the repetition frequency. This technique uses neither an acousto-optic modulator nor difference frequency generation. No synthesizer signals are needed aside from a reference signal to stabilize the repetition rate. We test the performance by comparing it with an independent comb system; it does not result in any performance degradation when compared with the conventional phase-locking method. The offset-free comb realized by this technique may become a powerful and universal tool for use in frequency-comb-related research.