A beam splitter is a high-precision tool used in experimental laboratories.
It is a glass cube made of several lab-grade glass prisms with special optical filtering coatings. This type is also called an x-cube.
A beam splitter’s purpose is to literally split a single beam of light into multiple beams. This may sound simple, but it requires fantastic precision.
They are typically used to separate a single laser beam into multiple beams, but this dichroic version can split a beam of white light into different regions of its spectra.
Try shining a light, such as a cell phone flash light, through one of the faces and see the different colors that make up the white light spill out the other sides. The process also works in reverse, shining the various colors into the sides combines them into a single light.
Beam splitters have been used in many complex physics experiments, such as measuring the speed of light, testing the behavior of photons, and demonstrating quantum entanglement. They are now commonly used in quantum computing development.