Holonyak Lab researchers look to improve VCSEL technology

The technology in the latest iPhone allows users to take 3D photos and unlock their phones with facial recognition using Vertical-Cavity Surface-Emitting Lasers, or VCSELs. Holonyak Lab’s John Dallesasse and several of his students are looking at how they can improve VCSEL technology for applications that include facial recognition and systems for autonomous vehicles.

“VCSELs are a type of device that are seeing broad use in a growing number of applications,” said Dallesasse, professor of electrical and computer engineering. “They are being looked at for use in self-driving cars that utilize LIDAR, and are already extensively used in the fiber optic networks of large data centers.” 

LIDAR operates similar to radar, except instead of radio waves it uses light to measure the relative speed and position of surrounding objects. For LIDAR applications, the shape of the light beam and amount of light that can be generated are important.

“We’re specifically looking at ways of improving the optical beam that comes out of the VCSEL,” said Dallesasse. “When you have a device like a VCSEL, the optical modes can be thought of as the light patterns on the surface. In order for you to utilize patterns, it’s desirable to be able to control those light patterns.”

The improved VCSEL technology could also be used in smartphones, 3D imaging, sensing, gesture recognition, and other similar applications where the quality of the optical beam is important. It’s also possible that this technique may help with multi-level modulation techniques, such as PAM-4, that are increasingly important for data links operating at 100 gigabits per second and higher.

Dallesasse’s group isn’t the only one interested in this fluid technology. II-VI EpiWorks supplied the semiconductor wafers needed to make the VCSELs, and the II-VI Foundation has contributed funding to the effort.

 The II-VI Foundation was formed to support the next generation of engineers, scientists, and mathematicians through an engaging graduate student program. The foundation funds graduate student research, but goes beyond funding by visiting campuses to meet with the students view research presentations. They also host a graduate student research conference each year at one of their facilities. These experiences are incredibly valuable for students like Dallesasse’s Patrick Su, Kevin Pikul, and Fu Chen “Alex” Hsiao. Pikul presented the work for the group at the 2019 meeting – his first presentation at a technical conference.

“It’s a very student-focused program that we’ve had students participate in for three years,” said Dallesasse. “They encourage all of the research updates to be written and given by graduate students. It’s a nice program from the standpoint of helping the graduate students develop presentation and technical writing skills in a low-risk environment.”

The history of this work can be traced back decades. The techniques applied by the current team use a technology developed by students of Nick Holonyak, Jr. in the early 80s. By combining the technology from Holonyak’s group known as impurity induced layer disordering with a technique developed by Dallesasse’s team called dielectric anti-phase filters, the modern team is able to make VCSELs that operate with a simple optical pattern (“single mode”) yet offer reasonably high output powers.

“Illinois as a whole is well known for work on devices like VCSELs,” said Dallesasse. “Oxidation was developed at Illinois. The first person to apply oxidation to the fabrication of VCSELs was an Illinois graduate, and other HMNTL professors are doing outstanding work on VCSELs.  This type of work goes back to EERL – the lab before the HMNTL building existed. There’s a lot of rich VCSEL history at Illinois.”