Optical device mimics both black and white holes

In the realm of general relativity, black holes are well-known for their ability to trap light and matter by bending spacetime, creating a point of no return. While black holes have fascinated scientists and the public alike, another concept, the white hole, has remained more theoretical. A white hole is thought to be the reverse of a black hole, expelling light and matter rather than absorbing them. Now, a team of researchers has designed a novel optical device with intriguing similarities with both these elusive cosmic phenomena.

The device, reported in Advanced Photonics, functions as an optical black hole or optical white hole, and rests on a principle known as “coherent perfect absorption” of light waves. Dependent on polarization, this optical device can either absorb or reject light almost entirely, analogous to the behavior of a gravitational black or white hole in space.

The device works by forming a standing wave from incident light waves, where interactions with an ultrathin absorber lead to perfect absorption or transmission, based on the polarization of the light. In simple terms, it behaves like a cosmic object that either swallows or repels light.

Senior corresponding author Nina Vaidya, professor at the University of Southampton (UK), remarks, “Celestial phenomena, especially black holes, have fascinated the imagination and exploratory intrigue of humans for generations. Analogs are ways of accessing physics, especially for faraway objects like black holes, as the mathematical frameworks and aspects of physical principles repeat themselves in surprising ways in several systems—celestial phenomena to nano- and pico-scale devices.

“We introduce the concept of optical black and white holes that deterministically absorb almost all light of one polarization while rejecting light of the orthogonal polarization. It relies on our experimental demonstration of broadband coherent perfect absorption in compact devices, enabled by spatial coherence and interference, while polarization sensitivity is acquired from the geometrical phase of the interfering beams.”

The team’s proof-of-concept experiments demonstrate that this optical device manipulates electromagnetic waves in a way that mirrors the behavior of gravitational black and white holes. Simulations illustrate the absence of reflection from the device for the black hole analog and the formation of a standing wave due to interference of incident and reflected light for the white hole.

The results illuminate fascinating insights and possibilities of manipulating light–matter interactions and may enable wide-ranging practical applications.

Vaidya notes, “Our optical device can be employed as an analog to study and explore the physics of these faraway celestial phenomena; or indeed to provide a practical framework for several potential applications of tailoring of electromagnetic waves and enhanced light–matter interactions, such as detection, energy conversion, multispectral camouflage, stealth technologies, and more.”