Transmission Experiment of 80-Gbit/s-Based WDM Signals Using an OPGW in the Field and In-service Chromatic Dispersion Monitering through Envelope Modulated WDM Signals

A field experiment on transmission 80-Gbit/s-based wavelength division multiplexing (WDM) signals is successfully carried out. In case of high speed transmission in the field, chromatic dispersion (CD) alteration caused by temperature change of the fiber becomes a serious problem. In order to keep fine transmission quality, it is necessary to control the dispersion of the transmission line in a suitable range by tuning dispersion compensators. For the sake of the adaptive control of the CD, an in-service dispersion monitoring technique for WDM transmission is proposed. The basic configuration of the method is shown in Fig. 1. The difference of the propagation delay between two channels caused by the CD of the transmission line is detected using signals superimposed on the envelope of the WDM pulses. Dispersion alteration of the transmission line is estimated from the measured delay in real-time. Fig. 2 is a schematic structure of the transmission experiments, where the proposed technique is involved. In the transmitter section, 40-Gbit/s RZ signals are multiplexed into 80-Gbit/s signals with a RZ format and the WDM signal having eight wavelengths is generated. Then a sinusoidal signal is superimposed on the envelope of the WDM pulses using another LN modulator. At the receiver end, delay difference between channels is measured by a phase comparator. After