Summary form only given. For multichannel systems over various types of fiber infrastructures, one option for increasing the throughput is the increase of the individual channel rate, which imposes an increase in the required signal-to-noise ratio (SNR) at the receiver, hence in the output power of in-line amplifiers. The other option is to increase the number of channels, with the total output power of the amplifiers set for an adequate SNR for all channels. However, should several channels not be transmitted, the power per channel rapidly increases, in absence of gain control, as in present commercially available systems. In both scenarios, self-phase modulation (SPM) can become the limiting factor. The experimental setup for the investigation of SPM-induced limitation at 10 Gbit/s is given. Various types of dispersive fibre are experimented with.