AN OPTICAL fibre 75 kilometres long has been transformed into the world’s longest laser, a feat its inventors hope will improve long-distance transmissions.
Because optical fibres lose 5 per cent of their power for every kilometre, the signal must be amplified. Now Juan Diego Ania-Castañón and his team at Aston University in Birmingham, UK, have dispensed with amplifiers by making the entire fibre behave like a laser. Lasers inject light at each end which continually excites some of the fibre’s atoms to a higher energy, so they emit photons of a longer wavelength.
These are reflected by mirrors at…
