Despite the ubiquity of VCSELs, found in everything from computer mice to face-scanning hardware in smartphones, these devices remain an active field of research, with many in the field exploring new applications. The laboratory of Kent Choquette at the University of Illinois Urbana-Champaign has developed a design in which light from multiple VCSELs combines to form a single coherent pattern called a “supermode.” The result of this combination is a controllable pattern that is brighter than what is possible with an array of independent devices, adding to the capabilities of the already versatile devices. A 940-nm dual-cavity photonic crystal VCSEL array with weakly anti-guided cavities supporting coherent supermode emission. Courtesy of the University of Illinois Urbana-Champaign. “VCSELs are more challenging to work with than other kinds of lasers because they naturally tend to emit light in many special patterns, or ‘modes,’ so the central problem has been figuring out how to get the light to stay in the mode you want,” said Choquette, a professor in the university’s Grainger College of Engineering. “The design we explore in this study is noteworthy because it shows how to extend mode control across more than one VCSEL and use an array of them in tandem to get a single desired mode. "With this level of cooperation across arrays of VCSELs, we’re confident that new uses for these devices will emerge.” Typically, VCSELs are individually controlled with electrical signals, which makes coordinating a coherent beam across laser cavities challenging. In the current work, the researchers designed a photonic crystal that connects adjacent VCSELs, enabling them to operate together. This approach allows control of both cavities to produce one of two predefined collective patterns, or supermodes. Dan Pflug, an Illinois Grainger Engineering graduate student in Choquette’s laboratory, and the lead author of the study, investigated the details of the design. Pflug looked at the use of a special “anti-guided” crystal to achieve the optical coupling. The Illinois team then turned the design over to the company Dallas Quantum Devices, where a working device was fabricated in a foundry-level process, demonstrating that the design can be practically realized. This research was published in IEEE Xplore (www.doi.org/10.1109/JPHOT.2025.3566986).
