A team of engineers at UC Berkeley and Lawrence Berkeley National Laboratory has solved a fundamental problem that has frustrated nanophotonics researchers for nearly two decades: how to deliver electricity to a nanoscale laser without degrading the very optical properties that make the device work.
The breakthrough, published Monday in Nature Nanotechnology, introduces a design called "orthogonal optoelectronics" that separates the electrical and optical functions of the device, allowing each to be optimized independently.
The Core Challenge
Nanophotonic lasers use structures smaller than the wavelength of light to trap and control photons. These devices require strong "index contrast" — a sharp difference in refractive index between the light-guiding structure and its surroundings — to tightly confine light. But powering such a device electrically typically requires adding conductive materials that reduce that contrast and degrade performance, creating an inherent conflict between "good optics" and "good electrical injection."
"This was a conflict we were trying to solve," said Emma Martin (Ph.D. '25 EECS), co-lead author of the study. "We wanted to create a structure that could be electrically powered without disturbing the optical cavity that makes the device work."
The Solution: Nano-Posts at the 'Sweet Spots'
The team's solution is elegantly simple. They support the device on an array of microscopic posts, or nanopillars, positioned precisely at the locations where the light's electromagnetic field naturally drops to zero. At these points, the posts conduct electricity while remaining effectively invisible to the light.
"Using this design, we achieved electrically powered lasing at room temperature at the wavelengths used in fiber-optic communications," said Md Ishfak Tahmid, co-lead author and Ph.D. student. "It's the first time current has been delivered uniformly across hundreds of these tiny cells while preserving the optical properties of the underlying photonic structure."
Unexpected Discovery
The researchers made an unexpected finding: their main limitation was not optical design but fabrication uniformity. The optical mode proved robust even with variations in nanopost size, but tiny inconsistencies strongly affected how uniformly current was injected across the device.
"This identifies a new design regime for electrically injected nanophotonic devices," said principal investigator Boubacar Kanté, professor of electrical engineering and computer sciences at UC Berkeley. "Future devices will require close co-design of optics, electronics, heat flow and nanofabrication."
Applications and Impact
The breakthrough could enable a new generation of compact, energy-efficient photonic technologies across multiple domains:
- Optical communications and fiber-optic networks - AI data centers, where energy-efficient photonic interconnects could replace power-hungry electrical links - LiDAR for autonomous vehicles - On-chip photonic systems for sensing and imaging - Quantum photonics and quantum computing
The research was supported by the Office of Naval Research, the NSF Quantum Leap Challenge Institutes program, the Bakar Prize and the Berkeley Emerging Technology Research Center.
