A beamsplitter is an optical device designed to divide a beam of light into two separate paths—one transmitted and one reflected. This is usually done by applying a thin-film coating on a glass substrate and angling the element relative to the incoming light. It is a crucial part of many optical experimental and measurement systems, such as interferometers, also finding widespread application in fibre optic telecommunications. a laser beam) into two (or sometimes more) beams, which may or may not have the same optical power (radiant flux).