The behavior of the beam splitter is core to the presence and reduction of noise due to vacuum fluctuations in LIGO, which injects a squeezed vacuum state into the empty input port of the beamsplitter to reduce coupling of quantum noise into the interferometer. A beam splitter or beamsplitter is an optical device that splits a beam of light into a transmitted and a reflected beam. It is a crucial part of many optical experimental and measurement systems, such as interferometers, also finding widespread application in fibre optic telecommunications. This allows for the creation of multiple light paths, which is essential in many optical setups.