In the realm of general relativity, black holes are well-known for their ability to trap light and matter by bending spacetime to create a point of no return. This is in contrast to the more theoretical white hole, which is thought to be the exact opposite — expelling light and matter rather than absorbing them. Now, a team of researchers has designed an optical device with similarities with both of these elusive cosmic phenomena. The device 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. It 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. This means that it behaves similarly to a cosmic object that either swallows or repels light. The device is based on a double prism design separated by a thin film that acts as a dark light absorbing plane. Courtesy of Nina Vaidya/University of Southhampton “Analogs are ways of accessing physics, especially for far away objects like the black holes, as the mathematical frameworks and aspects of the physical principles repeat themselves in surprising ways in several systems—celestial phenomena to nano- and pico-scale devices,” said senior corresponding author and University of Southampton professor Nina Vaidaya. 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. “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," continued Vaidaya. “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 researchers believe that their device may lead to better understanding the physics of black and white holes, and may be used in more practical applications where electromagnetic waves and light matter interactions might need to be tailored, such as multispectral camouflage, detection, and energy conversion, among others. The research was published in Advanced Photonics (www.doi.org/10.1117/1.AP.7.2.025001).