A system comprises signal paths. The source computer measures the network’s available bandwidth, forms a sequence of output packets from a sequence of data packets, and transmits the output packets over the network to the destination computer, where the transmission rate is ramped up to the measured bandwidth. Power of the input light signal is measured and the power of first and second backward pump lights proceeding in the opposite direction to the input light signal is controlled based on the measured power. In addition, a data storage device stores the first image and the second image, and an image processor, coupled to the data storage device, compares the first image with the second image.