Optical singularities could be used for a wide range of applications, from super-resolution imaging to optical trapping

When we think of singularities we tend to think of massive black holes in galaxies far away or the far future with AI on the run, but singularities are all around us. Singularities are just a place where certain parameters are undefined. The North and South Poles, for example, are what are called coordinate singularities because they do not have a defined longitude.

Optical singularities usually occur when the phase of light with a specific wavelength or color is undefined. These regions appear completely dark. Today, some optical singularities, including optical vortices, are being explored for use in optical communications and particle manipulation, but scientists are only beginning to understand the potential of these systems. The question remains: can we harness darkness as we harness light to create powerful new technologies?

Now, researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have developed a new way to control and shape optical singularities. The technique can be used to design singularities of many shapes, far beyond simple curved or straight lines. To demonstrate their technique, the researchers created a heart-shaped singularity sheet.

“Conventional holography techniques are good at shaping light, but have difficulty shaping darkness,” said Federico Capasso, Robert L. Wallace professor of applied physics and Vinton Hayes principal investigator in electrical engineering at SEAS and author main article. “We have demonstrated on-demand singularity engineering, which opens up a vast array of possibilities in a wide variety of fields, from super-resolution microscopy techniques to new atomic and particle traps. “

The research is published in Nature Communication.

Capasso and his team used flat metasurfaces with precisely shaped nanopillars to shape the singularities.

“The metasurface tilts the wavefront of light very precisely across a surface so that the interference pattern of the transmitted light produces large regions of darkness,” said Daniel Lim, graduate student at SEAS and first author of the article. “This approach allows us to accurately design dark regions with remarkably high contrast. “

Artificial singularities could be used to trap atoms in dark regions. These singularities could also improve very high resolution imagery. While light can only be focused on regions of around half a wavelength (the diffraction limit), darkness has no diffraction limit, which means it can be localized at any size. This allows darkness to interact with particles on length scales much smaller than the wavelengths of light. This could be used to provide information not only on the size and shape of the particles, but also on their orientation.

Artificial singularities could extend beyond light waves to other types of waves.

“You can also create dead zones in radio waves or silent zones in sound waves,” Lim said. “This research indicates the possibility of designing complex topologies in wave physics beyond optics, from electron beams to acoustics,” Lim said.

The Harvard Office of Technology Development has protected the intellectual property relating to this project and is exploring commercialization possibilities.