Four-wave mixing A weak optical signal (red) from a spacecraft transmitter can be amplified noise-free when it encounters two pump waves (blue and green) in a receiver on Earth. (Courtesy: Chalmers University of Technology/Rasmus Larsson) A new and practical approach to the low-noise amplification of weakened optical signals has been unveiled by researchers in Sweden. Drawing from the principles of four-wave mixing, Rasmus Larsson and colleagues at Chalmers University of Technology believe their...