Illinois prototype laser uses non-repeating pattern at 1.5 micrometers

At the University of Illinois Urbana-Champaign (UIUC), a semiconductor laser has produced a single-mode beam at room temperature even though the pattern guiding its light does not repeat. The proof-of-concept device emitted at 1.5 micrometers and was powered by an external light source—a method called photopumping—rather than electrical injection.

Photonic-crystal surface-emitting lasers, or PCSELs, use a carefully designed pattern to control how light moves through a semiconductor. The structure spreads light interaction across a large area and directs some of it through the surface, producing a narrow, controlled beam in a single optical mode. Conventional PCSELs generally rely on repeating patterns, however, which limits how freely engineers can vary the geometry.

That limitation is also a manufacturing problem. Changing the shape or spacing of tiny features can make fabrication difficult, and semiconductor regrowth can distort the geometry that was designed. The UIUC team’s buried-dielectric approach instead patterns a silicon dioxide layer before covering it with epitaxial semiconductor, helping preserve the features inside the device.

The new laser uses tiny silicon dioxide features with a lower refractive index, surrounded by semiconductor with a higher one. Their positions vary in a controlled quasi-periodic pattern rather than repeating at fixed intervals. Erin Raftery, a study author and UIUC PhD candidate, said the design offers more flexibility for tuning refractive-index variation; engineering professor Kent Choquette said different structures could eventually be mixed and matched on the same substrate.

Concretely, the near-term benefit is design flexibility, not a finished product: engineers could have more freedom to optimize lasers for sensing, communications, aerospace, defense and silicon-photonics lidar. The device remains a proof of concept, and its photopumped operation means it is not yet a practical diode laser. The reported performance also does not establish an advantage over conventional PCSELs on every measure. The team’s next goal is an electrically injected device.