A Michelson Interferometer is a device that combines light that has traveled in two perpendicular directions, aiming to detect small speed or distance changes by measuring the combined light's Interference. Albert Michelson developed this type of device to measure differences in the speed of light according to direction and famously found there were none.
Much larger devices of the same general design are used to attempt to detect Gravitational Waves.
Gravitational Wave (GW)
Imaging Fourier Transform Spectroscopy (IFTS)