UIUC Researchers Break Rigid Patterns in New Quasi-Periodic Semiconductor Laser
A new laser design replaces traditional repeating structures with non-periodic patterns to increase design flexibility and fabrication reliability.
Researchers at the University of Illinois Urbana-Champaign (UIUC) have developed a semiconductor laser that maintains precise light control without relying on traditional repeating patterns. This proof-of-concept device demonstrates that quasi-periodic structures can achieve stable lasing, potentially removing a major bottleneck in the fabrication of high-performance optical systems.
Published in the journal Applied Physics Letters, the study details a quasi-periodic photonic-crystal surface-emitting laser (QPCSEL) that successfully produced single-mode lasing at room temperature. The device operates at an emission wavelength of 1.5 micrometers. To ensure the structural integrity of the non-repeating pattern, the team utilized a "buried-dielectric" platform, where silicon dioxide features are patterned and subsequently covered with epitaxial semiconductor to preserve the geometry during the fabrication process. While the current prototype is photopumped—meaning it is powered by an external light source—the team has successfully demonstrated the underlying physics required for a practical device.
The Shift from Rigid Periodicity
Conventional photonic-crystal surface-emitting lasers (PCSELs) rely on strictly repeating, rigid geometries to control the movement of light. While effective, these periodic structures are notoriously difficult to manufacture and are highly susceptible to distortion during the semiconductor regrowth phase. The UIUC team sought to overcome these limitations by drawing inspiration from topologically protected patterns, testing whether a quasi-periodic design could provide the same level of control with greater flexibility.
"We’ve demonstrated that we can have a non-periodic pattern and more flexibility to tune it," said Erin Raftery, a PhD candidate at UIUC. "It’s a different way of engineering the refractive index variation to get the properties we want from our lasers."
Implications for Optical Engineering
This shift in design allows engineers to mix and match different photonic-crystal patterns on a single substrate, a feat that was previously impossible with standard growth methods. According to UIUC engineering professor Kent Choquette, the ability to combine multiple structures on one substrate could lead to the development of more reliable and better-performing lasers.
By removing the requirement for rigid periodicity, the QPCSEL approach simplifies the fabrication process and opens the door for highly customizable optical properties. This flexibility is critical for the next generation of compact optical systems, including silicon-photonics lidar, where precision and reliability are paramount.
The Path to Practical Application
Despite the successful proof-of-concept, the transition from a laboratory prototype to a commercial component requires further development. The primary hurdle remaining is the shift from photopumping to electrical injection, which would allow the laser to be powered by a standard electrical current rather than an external light source.
As the team works toward a practical, electrically driven device, the research establishes a new framework for semiconductor design. "We’ve demonstrated the physics," Professor Choquette noted. "Now we need to demonstrate a practical device."