ECE Illinois researchers develop new, higher-speed laser

ECE Illinois researchers have developed a new laser configuration that could potentially achieve higher speeds than a traditional vertical-cavity surface-emitting laser (VCSEL). The composite-resonator vertical-cavity laser (CRVCL), which currently has a modulation bandwidth of 12.5 GHz, has the capability to achieve up to 40 GHz, according to ECE Professor Kent Choquette, a Sony Faculty Scholar, and graduate student, Chen Chen.

According to Chen, the emergence of VCSELs represents a significant advance in optoelectronics and their applications. "CRVCLS are built upon VCSEL structures. Through a higher level of device integration, a VCSEL has evolved from a device with a single optical cavity and two electrical terminals to a CRVCL with two optically-coupled electrically-separately cavities and three electrical terminals (refer to Fig. 1)," he said. "CRVCLS gain additional functionalities and flexibilities over VCSELS, and thereafter they may be used for even wider applications.

Unlike a VCSEL, a CRVCL’s optical properties, such as threshold current, slope efficiency, and maximum light output, can be changed through one cavity while the electrical current into the other cavity is held constant, Chen said. (see Fig. 2)

Choquette said he has been working for more than a decade to discover a way to increase the modulation bandwidth, and is excited by his team’s progress. The team’s post-deadline research paper was one of only 24 papers recognized at the Conference on Lasers and Electro-Optics (CLEO) in May at the Baltimore Convention Center. "To get recognized at CLEO, which is the premiere lasers and applications conference in the world, is a big deal. It’s very competitive," said Choquette.

Choquette, who has been at Illinois nearly eight years and is the interim director of the Micro and Nanotechnology Lab, explained that the team is concentrating on ultimately achieving low-cost, high-performance lasers with more functionality. "If we can make lasers modulate faster, with lower power, there will be higher performance in optical networks," he said. "Cell phones and computers will work better. It directly enables the information network and moves information faster."

Chen has been focusing on CRVCLs for two years, during which he has spent a great deal of time fabricating the structure, said Choquette. Although Chen said he is happy about the recognition he and his colleagues in the Photonic Device Research Group have received, he acknowledged that it is still early in development and there may be some obstacles ahead. "CRVCLs contain very rich device physics, many of which aren’t fully understood," said Chen. "I think one of the greatest challenges is to relate the device characteristics, what I can see, to the physics - what it is really happening," said Chen.

Choquette said he is impressed with all the research students have been doing at Illinois. "We’re doing things here in an academic lab that I was doing in a national lab a few years ago," he said.

Portions of this work are funded by the National Science Foundation.