Accurate time/frequency transfer method using bidirectional WDM transmission

An accurate time transfer method is proposed using bidirectional wavelength division multiplexing (WDM) signal transmission along a single optical fiber. This method will be used in digital telecommunication networks to yield a time synchronization accuracy of better than 1 ns for long transmission lines over several tens of kilometers. The method can accurately measure the difference in delay between two wavelength signals caused by the chromatic dispersion in the fiber for conventional simple bidirectional dual-wavelength frequency transfer methods. We describe the characteristics of this difference in delay and show that the accuracy of the delay measurement can be obtained below 0.1 ns by transmitting 156-Mb/s time reference signals of 1.31 and 1.55 /spl mu/m along a 50-km fiber using the proposed method. Subnanosecond delay measurement using the simple bidirectional dual-wavelength transmission along a 100-km fiber with a wavelength spacing of 1 nm in the 1.55-/spl mu/m range is also shown.