Engineers at the University of Illinois Urbana-Champaign have achieved room-temperature lasing from a novel photonic-crystal surface-emitting laser, funded by a $1.5 million grant from the Air Force Research Laboratory. The team, led by Kent Choquette and Minjoo Larry Lee, replaced traditional air-hole photonic crystals with a buried dielectric layer of silicon dioxide, overcoming a key fabrication challenge and demonstrating a viable pathway towards more robust and efficient laser designs. This advance, detailed in the IEEE Photonics Journal, positions the technology for potential integration into applications such as autonomous vehicles and defence systems within the next twenty years.
Advancing Photonic-Crystal Surface-Emitting Laser Technology
Researchers at the University of Illinois Urbana-Champaign have demonstrated advancements in the fabrication of photonic crystal lasers, specifically addressing challenges related to maintaining structural integrity during the manufacturing process. The team, funded by the Air Force Research Laboratory, focused on improving the design of photonic crystal surface-emitting lasers (PCSELs), a relatively nascent field within semiconductor laser technology.
A primary obstacle in PCSEL development lies in the tendency for air holes – traditionally used to define the photonic crystal structure – to become filled with semiconductor material during regrowth, thereby compromising the uniformity of the crystal lattice. To mitigate this issue, the Illinois team substituted air holes with a solid dielectric material – silicon dioxide – preventing deformation during subsequent growth stages. This approach yielded a proof-of-concept design incorporating buried dielectric features within the semiconductor layer.
The successful integration of the amorphous silicon dioxide into the crystalline semiconductor structure was not assured, given the potential for disrupting the crystal’s uniformity. However, the team achieved lateral growth around the dielectric, successfully coalescing semiconductor material on top of the embedded features. This represents a significant step towards realising more robust and reliable photonic crystal lasers.
Potential applications for these improved devices extend to several sectors, including autonomous vehicles, laser cutting and welding, and free-space optical communication. The researchers anticipate that these technologies will mature over the next two decades. Current efforts are directed towards creating electrically-pumped devices, enabling operation via a current source rather than optical pumping.
Overcoming Fabrication Challenges with Dielectric Integration
The choice of silicon dioxide as a dielectric material presented a specific fabrication challenge. Unlike the crystalline semiconductor layers, silicon dioxide is amorphous – lacking a long-range ordered structure. Maintaining the integrity of the photonic crystal structure required careful control during regrowth to prevent the amorphous dielectric from disrupting the surrounding crystalline lattice. The team successfully navigated this issue by achieving lateral growth of the semiconductor material around the embedded dielectric features, allowing for complete coalescence of the crystal structure above the buried layer.
This approach to dielectric integration represents a departure from traditional PCSEL fabrication techniques. By eliminating air holes – a common source of structural instability – and replacing them with a solid dielectric, the Illinois Grainger engineers have demonstrated a pathway towards more robust and reproducible photonic crystal lasers. The successful implementation of this technique is anticipated to contribute to the broader development of PCSEL technology, paving the way for applications requiring high-performance laser sources.
Future Applications and Collaborative Development
Beyond the demonstrated proof-of-concept, ongoing research at Illinois Grainger Engineering focuses on transitioning the current optically-pumped device towards electrical operation. Achieving diode-pumped operation – powering the laser with an electrical current rather than light – is crucial for practical implementation in many target applications, including automotive and defense systems. This transition necessitates the development of suitable electrical contacts and optimisation of the semiconductor layers to facilitate efficient current injection and light emission.
The collaborative nature of this research is noteworthy, extending beyond the University of Illinois Urbana-Champaign to include the Air Force Research Laboratory. This partnership provides access to essential facilities and funding, while also ensuring alignment with strategic defense priorities. The team acknowledges the contributions of both Erin Raftery and the Minjoo Larry Lee group, highlighting the interdisciplinary expertise required to address the complex challenges inherent in advanced laser development. Further collaborative efforts are anticipated as the technology matures and moves closer to commercialisation.
The potential applications of these advancements in photonic crystal lasers extend beyond the previously mentioned sectors. The high brightness and narrow beam divergence characteristic of PCSELs make them particularly well-suited for LiDAR systems, offering improved resolution and range for applications such as battlefield mapping and autonomous navigation. Furthermore, the compact size and potential for high-volume manufacturing could enable integration into a wider range of devices, including advanced sensing systems and high-speed data communication networks. The development of robust and reliable photonic crystal lasers is therefore expected to have a significant impact on a diverse range of technologies in the coming decades.
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