In a first for the field, researchers from The Grainger College of Engineering at the University of Illinois Urbana-Champaign have reported a photopumped lasing from a buried dielectric photonic-crystal surface-emitting laser emitting at room temperature and an eye-safe wavelength. Their findings, published in IEEE Photonics Journal, improve upon current laser design and open new avenues for defense applications.
For decades, the lab of Kent Choquette, professor of electrical and computer engineering, have explored VCSELs, a type of surface-emitting laser used in common technology like smartphones, laser printers, barcode scanners, and even vehicles. But in early 2020, the Choquette lab became interested in groundbreaking research from a Japanese group that introduced a new type of laser called photonic-crystal surface-emitting lasers, or PCSELs.
PCSELs are a newer field of semiconductor lasers that use a photonic crystal layer to produce a laser beam with highly desirable characteristics such as high brightness and narrow, round spot sizes. This type of laser is useful for defense applications such as LiDAR, a remote sensing technology used in battlefield mapping, navigation, and target tracking. With funding from the Air Force Research Laboratory, Choquette's group wanted to examine this new technology and make their own advancements in the growing field.
"We believe PCSELs will be extremely important in the future," said Erin Raftery, a graduate student in electrical and computer engineering and the lead author of the paper. "They just haven't reached industrial maturity yet, and we wanted to contribute to that."
PCSELs are typically fabricated using air holes, which become embedded inside the device after semiconductor material regrows around the perimeter. However, atoms of the semiconductor tend to rearrange themselves and fill in these holes, compromising the integrity and uniformity of the photonic crystal structure. To combat this problem, the Illinois Grainger engineers swapped the air holes for a solid dielectric material to prevent the photonic crystal from deforming during regrowth. By embedding silicon dioxide inside the semiconductor regrowth as part of the photonic crystal layer, researchers were able to show the first proof of concept design of a PCSEL with buried dielectric features.
"The first time we tried to regrow the dielectric, we didn't know if it was even possible," Raftery said. "Ideally, for semiconductor growth, you want to maintain that very pure crystal structure all the way up from the base layer, which is difficult to achieve with an amorphous material like silicon dioxide. But we were actually able to grow laterally around the dielectric material and coalesce on top."
Members of the field anticipate that in the next 20 years, these new and improved lasers will be used in autonomous vehicles, laser cutting, welding, and free space communication. In the meantime, Illinois engineers will improve on their current design, recreating the same device with electrical contacts allowing the laser to be plugged into a current source for power.
"The combined expertise of Erin and members of the Minjoo Larry Lee group, as well as the facilities and expertise at the Air Force Research Laboratory on Wright-Patterson Air Force Base were necessary to accomplish this result," Choquette said. "We look forward to diode PCSEL operation."
Kent Choquette is an Illinois Grainger Engineering professor of electrical & computer engineering and is affiliated with the Holonyak Micro & Nanotechnology Laboratory. Choquette holds the Abel Bliss Professorship in Engineering.
Minjoo Larry Lee is an Illinois Grainger Engineering professor of electrical & computer engineering and is the director of the Holonyak Micro & Nanotechnology Laboratory. Lee is an Intel Alumni Endowed Faculty Scholar.
