A beam splitter divides incident light into reflected and transmitted beams at a specified R/T ratio. For a lossless beam splitter, R + T = 1. It is a crucial part of many optical experimental and measurement systems, such as interferometers, also finding widespread application in fibre optic telecommunications. See the Comprehensive Guide for worked examples, SVG diagrams, and full references. Beamsplitters are often classified according to their construction: cube or plate. A beamsplitter is a common optical component that partially transmits and partially reflects an incident light beam, usually in unequal proportions.