Light Helps the Transistor Laser Switch Faster

Experiment: Light stimulates switching speed in the transistor laser. (Source: L. Brian Stauffer)

Experiment: Light stimulates switching speed in the transistor laser. (Source: L. Brian Stauffer)

Light and electrons interact in a complex dance within fiber optic devices. A new study by University of Illinois engineers found that in the transistor laser, a device for next-­generation high-speed computing, the light and electrons spur one another on to faster switching speeds than any devices available. Milton Feng, the Nick Holonyak Jr. Emeritus Chair in electrical and computer engineering, found the speed-­stimulating effects with graduate students Junyi Qiu and Curtis Wang and Holonyak, the Bardeen Emeritus Chair in electrical and computer engineering and physics.

As big data become bigger and cloud computing becomes more commonplace, the infra­structure for trans­ferring the ever-­increasing amounts of data needs to speed up, Feng said. Traditional techno­logies used for fiber optic cables and high-speed data trans­mission, such as diode lasers, are reaching the upper end of their switching speeds, Feng said.

“You can compute all you want in a data center. However, you need to take that data in and out of the system for the user to use,” Feng said. “You need to transfer the information for it to be useful, and that goes through these fiber optic inter­connects. But there is a fundamental switching limi­tation of the diode laser used. This techno­logy, the transistor laser, is the next-­generation techno­logy, and could be a hundred times faster.”

Diode lasers have two ports: an electrical input and a light output. By contrast, the transistor laser has three ports: an electrical input, and both electrical and light outputs. The three-port design allows the researchers to harness the intricate physics between electrons and light. For example, the fastest way for current to switch in a semi­conductor material is for the electrons to jump between bands in the material in a process called tunne­ling. Light photons help shuttle the electrons across, a process called photon-assisted tunne­ling, making the device much faster.

In the latest study, Feng’s group found that not only does photon-­assisted tunneling occur in the tran­sistor laser, but that it in turn stimulates the photon absorp­tion process within the laser cavity, making the optical switching in the device even faster and allowing for ultra-high-speed signal modulation.

“The collector can absorb the photon from the laser for very quick tunneling, so that becomes a direct-voltage-modulation scheme, much faster than using current modulation,” Feng said. “We also proved that the stimulated photon-assisted tunne­ling process is much faster than regular photon-­assisted tunne­ling. Previous engineers could not find this because they did not have the tran­sistor laser. With just a diode laser, you cannot discover this.

“This is not only proving the scientific point, but it’s very useful for high-speed device modu­lation. We can directly modulate the laser into the femto­second range. That allows a tremendous amount of energy-efficient data transfer,” Feng said. The resear­chers plan to continue to develop the tran­sistor laser and explore its unique physics while also forming industry partner­ships to commer­cialize the techno­logy for energy-­efficient big data transfer. (Source: U Illinois)

Reference: M. Feng et al.: Intra-cavity photon-assisted tunneling collector-base voltage-mediated electron-hole spontaneous-stimulated recombination transistor laser, J. Appl. Phys. 119, 084502 (2016), DOI: 10.1063/1.4942222

Link: High Speed Integrated Circuits Group (M. Feng), Dept. Electrical and Computer Engineering, University of Illinois, Champaign, USA

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