Wavelength conversion and in-band crosstalk in WDM optical networks

Abstract

Wavelength-routed all-optical networks have emerged as a popular architectural solution for wide area networks and are being conceived for future broadband communications. Call connection probability in such networks depends on the number of WDM wavelengths employed and on the capability for wavelength conversion at network nodes. Equipping all the network nodes with wavelength conversion capability to reduce the blocking probability is not a cost effective solution due to the high cost of wavelength converters (WC). Hence, networks equipped with converters at only some of the nodes are more practical. However, these nodes should be identified optimally so that network blocking probability is minimized. In this paper, wavelength converters based on four wave mixing (FWM) in semiconductor optical amplifiers (SOAs) is considered. In WDM all-optical networks, in-band crosstalk is regarded as one of the major transmission impairments. In-band crosstalk usually arises when multiple signals at identical or adjacent wavelengths pass through an optical crossconnect node. In-band crosstalk leads to increased receiver BER. This paper considers in-band crosstalk arising in a network which is equipped with wavelength converters. For every dynamically arriving connection request, a route is determined using Dijikstra’s algorithm and a free wavelength is determined using the random wavelength assignment. If no common free wavelength is available, connection is tried using wavelength converters, if available, on the given route. If wavelength assignment does not succeed, the call is blocked. If wavelength assignment succeeds, the BER at the destination node is computed before establishing the lightpath. If the estimated BER exceeds 10−12, the call is blocked. Otherwise, the call is admitted. The results reveal that wavelength converters are not useful in networks that already suffer from crosstalk conditions.