Graduate students Junyi Wu and Curtis Wang and professor Milton Feng found that light stimulates switching speed in the transistor laser, a device they hope will usher in the next generation of high-speed data transmission. Credit: Photo by 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.
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. 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,”…the transistor laser, is the next-generation technology, and could be a hundred times faster.”
Energy band diagram of a transistor laser with quantum well (QW) photon generation in the base and intra-cavity photon-assisted tunneling (ICPAT), i.e., photon absorption in the collector for excess base hole and electron re-supply.
Diode lasers have 2 ports: an electrical input and a light output. By contrast, the transistor laser has 3 ports: an electrical input, and both electrical and light outputs. The 3-port design allows the researchers to harness the intricate physics between electrons and light. Eg 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. 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.
From transistor laser L-VCE curves (L = coherent light intensity), the photon output reduction (absorption) can be obtained by subtracting the difference between constant output without ICPAT (dashed lines) and the actual observed output (solid lines). The light output without ICPAT is expected to be flat in the high VCB regime.
“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.
https://news.illinois.edu/blog/view/6367/336751
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