Need for speed: Choquette explores coupled device theory to improve laser modulation

10/14/2022 3:35:17 PM Lauren Laws

If you're reading this right now, that's probably because of the internet. Many of us use it every day for both work and pleasure. Transmitting all of that data requires the internet infrastructure which includes optical fibers, lasers, and detectors. As the internet has grown over the years, so too has the demand for more bandwidth, which means creating lasers that can modulate even faster than before. Unfortunately, there are always limitations. 

Kent Choquette
Kent Choquette

"We just can't directly modulate any faster."  

It's a familiar problem for ECE and HMNTL Professor Kent Choquette. He's spent more than twenty years working on semiconductor lasers including a particular type of laser diode, the vertical cavity surface emitting laser (VCSELs). Recently he and Photon Sciences Inc., received a grant from the U.S. Navy to continue working on a solution. His idea? Use two lasers as a coupled device instead of modulating a single laser.  

The goal is to design the laser to operate at 100 gigabits per second. Present day commercial devices can be directly modulated up to 30 gigabits per second. While the concept pursued is theoretical, Choquette and his partners demonstrated in phase one of their program that 70 gigabits is possible.  

"One of the payoffs is that if we can improve the performance of these arrays, we can also get increased power all integrated into a single device. Basically, chip scale technology," said Choquette. 

Current VCSEL technology already uses multiple lasers at a time from arrays for sensing but the lasers operate independent of each other. By coupling two together and tailoring their condition, Choquette hopes to reach the 100 gigabit threshold.   

"This is something new that's never been applied because we've never needed to do this before," he said. 

Funding for this came through the Small Business Initiative Research (SBIR) program. In this instance, the navy went to Photon Sciences Inc. to develop a high speed vicsel for their next generation fighter plane. However, this research could have broader applications. 

"The welding that is done in airplane and automobile manufacture are done with fiber laser welding that are being driven by semiconductor pump lasers. These hybrid systems that they're using are inefficient," said Choquette. Thus the ideas used to increase the modulation bandwidth could also lead to improved high brightness laser arrays. 

While 100 gigabit data modulation is the goal, Choquette explained the journey of discovery with his graduate students is just as important. Working on challenging problems he said provides his students a chance to explore and learn.  

"I tell my students we design widgets, we fabricate widgets, we test widgets, and then we rinse and repeat," Choquette explained. "We try to learn from every iteration, and that's why this work has evolved over the years."