The pioneering work in development of femtosecond frequency combs (FFC) was based on mode-locked Ti:Sapphire lasers [1,2]. Subsequently, work on development of similar systems built upon femtosecond fiber lasers was started by a number of groups [3-5]. The motivation was due in part to the direct spectral coverage in the 1 to 2 micron region as well as the now familiar arguments of low cost, portability, established technological infrastructure, footprint, etc., inherent within a fiber laser-based system. Moreover, as an FFC will be a necessary component (the clockwork) in practical implementations of optical atomic clocks, the potential for longer term, continuously phase-locked operation of fiber-laser based FFC (due its all fiber optical containment) offers additional motivation to pursue their development.
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