Analysis of evolution of over-modulated supervisory data in a cascade of All-Optical Wavelength Converters.

摘要

For the management of wavelength-division multiplexed (WDM) networks, it is important to identify each channel [1]. A way to do so consists in adding to each channel a low-depth modulation around a sub-carrier frequency [2]. Each time a channel goes through a wavelength-translating crossconnect, the information carried by the over-modulation must be removed and replaced by a new one. If all-optical wavelength converters (AOWC) are used, it has been shown that the non linear transfer function of these devices (in our case based on Mach-Zehnder interferometers and semiconductor optical amplifiers (SOA) [3]) could naturally erase the over-modulation [4]. It has also been proposed to use an active erasing scheme [5] to reach the same objective. However, no previous study has considered the behavior of AOWCs when cascaded. It is the objective of this paper to propose a more accurate understanding of this issue and we show, by experiment and simulation, that in fact the over-modulation, although it seems to be removed very efficiently after one wavelength converter will partially re-appear after a cascade of AOWCs due to mixing with the high bit-rate information, thereby confirming the need for active erasure.