Fiber-optic time and frequency transfer based on RF carrier phase and pseudorandom noise code

A system based on self-made modems and off-the-shelf fiber-optic devices aiming at achieving precise fiber-optic time and frequency transfer based on radio frequency (RF) carrier phase tracking and pseudorandom noise code correlation is demonstrated. The RF carrier phase and the pseudorandom noise code are both used through the fiber-optic link in the two-way mode. The two-way transfer asymmetry caused by the different optical wavelengths for both directions, which is the case in DWDM system, is avoided by the Code Division Multiple Access (CDMA) system here. The first result of the common clock experiment shows that the measurement noise characterized as modified Allan deviation of 6.5×10^-11 τ^-3/2 (1s to 1000s) and 2×10^-15τ⁰ (1000s to 10000s) with carrier phase and 2.5 × 10^-11τ^-1 (1s to 10000s) with code.