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Experimental assessment of intra-node crosstalk in a labelled system based on MZI wavelength converters

Optical label switching (OLS) is a promising technique for switching internet protocol (IP) packets in WDM networks. By using short fixed-length labels, the core nodes of the network can forward/switch packets quickly and efficiently while keeping the payload data entirely in the optical domain. A combined frequency-shift keying/intensity modulation (FSK/IM) scheme is a strong candidate for such an optical data router because of the simple label swapping mechanism and the scalability to higher data rates. In this combined modulation scheme, the payload is intensity-modulated and the label is frequency modulated. When reaching an optical node, the label is separated from the payload and is subsequently processed. A new label will be created and re-inserted together with the payload to form a complete data packet. During the label processing, the payload remains unchanged in the optical domain. When passing a number of optical nodes, one of the main network impairments is the spectral misalignment between the central wavelength of the modulated signal and the wavelength-selective element of the nodes, such as arrayed-waveguide (AWG)-based optical filters. As the various packet bursts are carried on multiple wavelengths, this spectral misalignment will inevitably increase the network’s susceptibility to optical crosstalk. From an intra-node point of view, it may lead to crosstalk effects in the intensity-driven wavelength converter, which is based on a Mach-Zehnder Interferometer (MZI) structure. In this paper, we report on the intra-node crosstalk effects in a pure IM system and an FSK/IM labelled scheme for different values of the wavelength spacing of the interfering channels.