Anapole Lasers Generate Ultrafast Pulses for Managing Nanoscale Optics

Anapole lasers made from semiconductors shaped into energy-storing nanodisks could be useful as an energy source for nanoscale optics in silicon-compatible platforms.

According to researchers from King Abdullah University of Science & Technology (KAUST), the lasers could be made small enough to fit onto computer circuit boards while retaining the ability to shape and control laser pulses for manipulating things such as data switches, biomedical implants and solar cells. In the anapole state, the laser does not emit energy in any direction and traps light inside the nanodisk.

The complex flashing patterns of fireflies (left) led KAUST researchers to develop anapole lasers that use interactions between energy-storing nanodisks (center) to generate high-speed pulses of light on microchips (right). Courtesy of ref 1. Gongora et al.

“The challenge of reducing an optical source down to the nanoscale is that it starts to emit energy strongly in all directions. This makes it almost impossible to control.” said Andrea Fratalocchi, an associate professor at KAUST.

The researchers developed a nanoscale laser based on a tightly confined anapole mode. By harnessing the non-radiating nature of the anapole state, they were able to engineer nanolasers based on InGaAs nanodisks as on-chip sources with unique optical properties.

Leveraging the near-field character of anapole modes, the team demonstrated a spontaneously polarized nanolaser able to couple light into waveguide channels four orders of magnitude greater in intensity than classical nanolasers. In addition the team was able to generate ultrafast (100 femtosecond) pulses via spontaneous mode locking of several anapoles.

Based on simulations on the quantum electrodynamics of photons, researchers showed that the light–matter interaction in a nanolaser emitting at the anapole frequency could give rise to a surprisingly stable steady state, where light energy was strongly collected within the anapole and evanescently transmitted in a subwavelength area outside the nanostructure.

Such an “anapole nanolaser” could be used for a range applications, from efficient energy coupling to ultrafast pulse generation without the need of external design elements.

Fratalocchi said that the nanolasers would appear invisible to an observer until perturbed by a nearby object. Consequently, arranging the cylindrical light sources into a loop could produce a chain reaction of light emissions, tunable down to as small as femtosecond (fs) pulse times.

“You can think of this laser as an energy tank — once the laser is on, it stores light and doesn’t let it go until you want to collect it,” he said.

Anapole nanolasers could offer a useful platform for monolithically integrated, silicon photonics sources for advanced and efficient nanoscale circuitry. The team’s models suggest that integrating different loops of anapole nanolasers could produce oscillating, dynamic patterns useful for reproducing brain-like activities, such as machine learning and memory retrieval, at low cost.

“It's really like a population of fireflies, where the individuals synchronize their emissions into beautiful patterns,” Fratalocchi said. “When we place the nanolasers close together, we can get similar control over the pulses.”

The research was published in Nature Communications (doi:10.1038/ncomms15535).