Function and Principle Diagram of a Beam Splitter

A beam splitter is an optical device that divides an incoming light beam into transmitted and reflected beams, typically constructed as a cube, plate, or pellicle with specialized coatings.Cube Beam SplittersCube beam splitters are made by cementing two right-angle prisms together at their hypotenuse faces using optical adhesives such as polyester, epoxy, or urethane-based resins . The hypotenuse of one prism is coated with a partially reflective material, which can be a thin metallic layer like aluminum or a dielectric multilayer stack. This coating determines the split ratio of reflected versus transmitted light. The cube design provides mechanical stability, protects the coating, and minimizes lateral displacement of the output beams .Plate Beam SplittersPlate beam splitters consist of a thin, flat glass or plastic substrate with a partially reflective coating applied to one surface . The second surface often has an anti-reflection coating to reduce unwanted reflections. Plate splitters are typically used at a 45° angle of incidence, which deflects one beam by 90° relative to the other. They are lighter, more compact, and cost-effective compared to cube splitters, but the transmitted beam may experience a slight lateral shift .Pellicle Beam SplittersPellicle beam splitters use an ultra-thin membrane of optical film stretched over a frame . The membrane is only a few micrometers thick, which eliminates ghosting and lateral beam displacement. Pellicles are delicate and mainly used in low-power or high-precision applications, such as interferometry or photography.Polarizing Beam SplittersPolarizing beam splitters, such as the Wollaston prism, are made from birefringent materials that split light into two beams with orthogonal polarization states . These are used when polarization separation is required, for example in optical isolation or interferometric setups.Coatings and MaterialsThe partially reflective coating is critical for controlling the split ratio. It can be a metallic film (e.g., aluminum) or a dielectric multilayer stack, engineered to achieve specific reflection/transmission ratios, such as 50/50 or 70/30 . The choice of substrate, coating, and geometry depends on the wavelength, polarization, and power of the light source, as well as the mechanical and optical requirements of the system. In summary, the structure of a beam splitter involves a combination of optical substrates, coatings, adhesives, and geometric configurations designed to split or combine light efficiently while minimizing optical distortions and maintaining mechanical stability .