Passively phase-locked Er:Fiber frequency comb

Modern precision metrology ever more strongly relies on the availability of optical frequency combs. We review our approach to passive stabilization of the carrier envelope phase (CEP) of a pulse train at full repetition rate via difference frequency generation. Using this approach, we demonstrate a inherently offset-free Er:fiber comb directly locked onto an optical reference (⁸⁵Rb) together with a possibility of an actively narrowed sub-500 mHz linewidth. This performance highlights an attractive potential of robust all-fiber comb systems toward applications in ultrahigh-precision metrology.