A Robust Frequency Stabilized of Er:Fiber Frequency Comb with Relative Frequency Instability of E-18

Highly stable and long-term frequency-controlled femtosecond optical frequency comb is demonstrated in this paper. We stabilized carrier envelope offset frequency onto a RF reference and obtained the in-loop frequency instability is about $4.3\times 10^{-18}{@} 1\mathrm{s}$ . We stabilized repetition rate onto an ultrastable laser. The relative frequency instability is $5.3\times 10^{-18}{@}1\mathrm{s}$ .