Frequency transfer of optical standards through a fiber network using 1550-nm mode-locked sources

High-stability transfer of harmonics of the pulse repetition frequency of a mode-locked fiber laser through a fiber network is demonstrated. The passive transfer instability is < 3 × 10^-14 for a 1-s averaging time, comparable with the optical-carrier frequency transfer of a narrow-linewidth CW laser. With active cancellation of the fiber-transmission noise, the transfer instability of this radiofrequency signal is below 7 × 11^-15 τ^-12/ for an averaging time τ ≥ 1 s, limited by the noise floor of the frequency-counting system. The noise cancellation reduces the rms timing jitter, integrated over a bandwidth from 1 Hz to 100 kHz, to a record low of 70 (20) fs for a 6.9 (4.5) km-round-trip installed (laboratory-based) fiber network.