Channel pre-emphasis equalization for a 40×40Gbit/s WDM system

The optical channel pre-emphasis equalization for a 40×40Gbit/s WDM transmission system is experimentally researched in this paper. In our experimental system, three EDFAs are concatenated as booster amplifier. The output spectrum imbalance is 5.0dB, 12.2dB and 7.6dB respectively with input transmitter signal power of 4.5dBm, 0.0dBm and -5.0dBm to EDFA1. For EDFA2 the output spectrum imbalance is 2.3dB, 4.4dB and 7.7dB respectively when input power is 4.5dBm, 0.0dBm and -6.7dBm, and the imbalance is 3.6dB, 5.6dB and 8.6dB for EDFA3 with the same set of input power. The power imbalance of the output spectrum after three spans of 270km changes with the different input power to each EDFA in the system. With the input power to three EDFAs is 5.7dBm, 7.4dBm and 8.0dBm respectively, the output signal spectrum imbalance is about 9.8dB. But with the appropriate input power of 5.2dBm, 3.4dBm and 3.3dBm to three EDFAs respectively, the spectrum imbalance is reduced to 4.3dB. When the input power to three EDFAs are 4.5dBm, 2.2dBm and -3.7dBm, the power imbalance is 9.4dB. The results indicate that, an appropriate choice of input power to three EDFAs, the output signal spectrum after propagation 270km can be equalized to the most extent. With this pre-emphasis equalization, the merit of benefit can be around 5.5dB. Although the equalizer is still necessary, but the requirement for the equalizer is greatly released. The OSNR degradation for the pre-emphasis equalization case is also examined, and about 1.0dB additional degradation is sacrificed. To take into the transmitter signal spectrum imbalance into account, the imbalance of the gain spectrum among 40 channels almost matches that of output signal power spectrum, but the difference is also evident at some channels. Finally, RA pump power is also optimized, and another 1.3dB improvement of channel balance can be achieved.