English: This animation depicts the basic principles of gravitational waves detection using an interferometer. Light from the laser is split into the two arms and recombined after bouncing of the mirrors. The phase difference creates constructive or destructive interference, determining how much light reaches the photodiode. When gravitational waves (emitted here by a binary black hole) reach the interferometer, the mirrors move, modulating the phase and thus the light reaching the photodiode, allowing to reconstruct the signal. The amplitude of the mirrors displacements is vastly exaggerated for the animation purpose, as is the phase change. The optical components were taken from the ComponentLibrary vector graphics library designed by Alexander Franzen (http://www.gwoptics.org/ComponentLibrary). The waveform was generated with the SEOBNRv4 model, using the PyCBC software ; the masses for the black holes are both 80 solar masses.