Semiconductor lasers could become more flexible and reliable thanks to a new design that breaks away from the repeating patterns traditionally used to control light.
Researchers at the University of Illinois have developed a new type of photonic-crystal surface-emitting laser, or PCSEL, using a partially nonrepeating structure.
The approach could eventually help engineers build advanced lasers that are easier to tune for different applications.
PCSELs have attracted growing interest over the past two decades because they can produce high-quality laser beams and may be useful in areas such as aerospace and defense.
These lasers usually contain photonic crystals—carefully designed microscopic structures that control how light moves through a material.
Traditionally, the patterns in these photonic crystals repeat regularly across the device. While this arrangement works well, it also creates limitations. The performance of the laser can depend strongly on the exact geometry of the repeating pattern, making it difficult to produce devices with a wide range of designs and properties.
A team led by electrical and computer engineering professor Kent Choquette wanted to find a more flexible approach. Graduate student Erin Raftery explored whether a laser could operate using a structure that was not completely periodic.
Inspired by research on nonrepeating patterns, Raftery combined this idea with a buried dielectric platform previously developed by the Illinois team.
Instead of simply etching tiny holes vertically through layers of semiconductor material, the researchers patterned a layer of silicon dioxide and then covered it with semiconductor material grown on top. This buried the patterned layer inside the device.
The result was a quasi-periodic photonic-crystal surface-emitting laser, or QPCSEL. Importantly, the device successfully produced laser light at room temperature, showing that the unusual structure could work under practical conditions.
“We’ve demonstrated that we can have a nonperiodic pattern and more flexibility to tune it,” Raftery said. She explained that the design provides another way to control variations in the material’s refractive index, which determines how light travels through the laser.
One major advantage is manufacturing flexibility. With conventional approaches, researchers may be limited to producing one type of structure at a time. The buried dielectric method could allow different patterns to be created on the same semiconductor substrate.
“Right now, you can only grow one kind of structure at a time, whereas we can mix and match on the same substrate,” Choquette said. This flexibility could ultimately lead to lasers that are more reliable and perform better.
The researchers have so far demonstrated that the underlying physics works. Their next goal is to turn the concept into a more practical device by developing an electrically powered laser diode.
If successful, the technology could open new possibilities for highly tunable semiconductor lasers designed for a wider variety of commercial and technological applications.
