In this paper, a numerical investigation on the limits of the optical frequency shift keying (FSK) label coding technique is presented, as well as an optimization of the critical parameters involved into it. The principle of the technique concerns a typical FSK modulated label, combined with an intensity modulated (IM) payload on the same optical carrier, via four-wave mixing (FWM) in a semiconductor optical amplifier (SOA). Simulations have been carried out for an intensity modulated nonreturn to zero (NRZ) 10-Gbs payload combined with a 625-Mbs FSK modulated header. The influence of the key parameters of the method such as the extinction ratio (ER) of the signal, the dynamic range of the FWM module and the FSK tone spacing have been investigated in combination with the system limitations,related to the propagating distance and the number of intermediate label swapping nodes. A 2R regeneration stage responsible for the label removal and reinsertion,and for the payload wavelength conversion and regeneration, has been adopted,based on a single Mach-Zender interferometer (MZI)-SOA stage. The FSK encoded label transmitter includes a compensation scheme for the removal of the residual amplitude intensity effect that FSK label causes on the IM modulated payload. A detailed numerical model has been implemented for the description of the FWM, due to its decisive role in the proposed architecture. It was found that it is possible to have successful (Q factor higher than 6 for both payload and header) transmission over five, 50-km spaced hops and assuming 10-Gbs payload with 625-Mbs header.
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