Bit error rate reduction by power shaping in WDM networks with EDFAs

Abstract The trend in multi-wavelength optical networks is toward dynamic route and wavelength assignment to support burst-switching or packet switching. Where erbium-doped optical amplifiers (EDFAs) are used for multi-wavelength amplifications, the time interval between traffic blocks can be long enough to induce EDFA optical power transients created by abrupt changes in the average input power to the EDFAs and can adversely affect the performance of the network. To mitigate the effects of EDFA optical power transients on optical networks, a method based on power shaping where heads and tails are joined to the beginning and end of a traffic block is proposed. A head (tail) gradually increases (decreases) the channel power by employing a pseudo-random bit sequence in which the probability of a “1” (“0”) increases from 0 to 0.5. This paper reports experimental results showing that EDFA optical power transients can be significantly reduced with adequate shaping periods. The effects of alternative shaping profiles are examined, and for a linear shaping profile, experiments show that the drop transient deviation is reduced by 0.5 dB while the add transient deviation is reduced by 0.71 dB. We show by lab experiments that the bit error rate induced by wavelength add-drop transients in a chain of EDFAs in an emulated fiber network can be reduced by 25% using power shaping techniques. Power shaping is an economical means of suppressing EDFA optical power transients compared to other physical layer approaches that require the addition of specialized components and can be applied to EDFAs as well as other solid-state and Raman optical amplifiers.