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. If we neglect the three-dimensional character of the electromagnetic fields and focus on one-dimensional propagation only, we can regard a beam splitter simply as a dielectric plate, possibly consisting of several y consisting of several layers ropagation along. 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.