Generation of correlated dual frequency combs in fiber lasers for high-precision metrology

Intracavity Phase Interferometry (IPI) has evolved into a powerful technique for high-precision metrology. In this method a parameter to be measured imparts a phase shift onto a pulse circulating in the laser cavity. The phase shift becomes a frequency shift applied to the corresponding frequency comb, which is measured by interfering the shifted comb with a reference comb created in the same laser cavity. Although fiber lasers are ideal for implementation of IPI, there are several challenges to achieve a deadband-free fiber IPI sensor. The huge amount of phase coupling between crossing pulses eliminates the small signal response. A successful observation of a beat signal was achieved in a polarization maintaining mode-locked fiber laser operating with orthogonally polarized pulses.