In the 21st century high power were adopted as an industrial material processing tool, and were expanding into other markets including the medical and scientific markets. One key enhancement enabling penetration into the scientific market was improvement in high finesse fiber amplifiers, which became able to deliver single frequency linewidths (<5 kHz) together with excellent beam quality and stable linearly polarized output. An optical amplifier typically consumes 25 W/fiber (bidirec-tional) and is placed every 80 km. Abstract Both bandwidth demand and energy consumption of ICT and communication networks is increasing and optical networks are regarded to provide high bandwidth solutions while enabling more energy efficiency. Typically, inputs and outputs are laser beams (very rarely other types of light beams), either propagating as Gaussian beams in free space or in a fiber. This amplification process requires energy, and that energy is drawn from a power source, typically the mains electricity supply.
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