Study outlines a new way to control light using black phosphorus

Caltech professor Harry Atwater and a team of co-authors published a new paper describing a new method of controlling light using an extremely thin material. In the research, the scientists used three layers of phosphorus atoms creating material capable of polarizing light that is tunable, precise, and thin. One of the best examples of a common item we are all familiar with that relies on polarized light to create readable characters is the screen of a calculator.The researchers note that black phosphorus is similar in some aspects to graphite or graphene. Both graphite and graphene are forms of carbon that form in layers only a single atom thick that is perfectly flat. Black phosphorus is different, creating ribbed layers (seen in the image above) and having an appearance that is very similar to corduroy. One critical aspect of blank phosphorus is that the material has significantly anisotropic optical properties. Anisotropic means the material is angle-dependent.

Being anisotropic is a critical feature of the material because, unlike graphene, where light is absorbed and reflected the same no matter which angle it is polarized at, black phosphorus aligns the polarization of light along its corrugations. That property allows black phosphorus to respond differently to light when it's aligned perpendicular to the material's corrugations.

When polarized light orients across the corrugations of black phosphorus, it has interactions with material that are completely different than when the light is oriented along with the corrugations. Anyone who's ever rubbed their hands along corduroy material is familiar with the difference in feel when rubbing a finger across the material's ribs or with the ribs.

What makes black phosphorus special is that it's also a semiconductor. The semiconductor capability allows structures to be constructed using black phosphorus to control light polarization when an electrical signal is applied. Combining the properties of the material for polarized light reflection and semiconducting capability, researchers were able to create small elements able to convert the polarization of light into a different reflected polarization state when the semiconductor is on or off. The discovery has the potential to revolutionize telecommunications, according to Atwood. It could also lead to new technology replacing Wi-Fi based on light, known as Li-Fi.