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Light helps transistor lasers switch more quickly

Photo: L Brian Stauffer

A study by an engineering team from the University of Illinois has found that light and electrons can work together in transistor lasers to produce faster switching speeds than in any other device.

According to Milton Feng, chair of electrical and computer engineering, the technologies used for fibre optic cables and high speed data transmission, including diode lasers, are reaching the upper end of their switching speeds. “You can compute all you want in a data centre,” he said. “However, you need to transfer the information for it to be useful – and that goes through fibre optic interconnects. But there is a fundamental switching limitation of the diode laser used. The transistor laser is the next generation technology and could be 100 times faster.”

While diode lasers have two ports – an electrical input and a light output – the transistor laser has three ports – an electrical input and electrical and light outputs.

The three port design is said to allow the researchers to harness interaction between electrons and light. The team says the fastest way for current to switch in a semiconductor is by tunnelling and that photons make the device perform faster through photon assisted tunnelling.

Feng’s group has not only found that photon assisted tunnelling occurs in the transistor laser, but that it also stimulates the photon absorption process within the laser cavity. This speeds optical switching and allows for ultra high speed signal modulation.

“The collector can absorb the photon from the laser for very quick tunnelling, so that becomes a direct voltage modulation scheme – much faster than using current modulation,” Feng said. “We also proved that stimulated photon assisted tunnelling is much faster than regular photon assisted tunnelling.

“This is very useful for high speed device modulation. We can modulate the laser directly into the femtosecond range. That allows a tremendous amount of energy efficient data transfer,” Feng concluded.

The researchers plan to continue to develop the transistor laser and explore its physics, whilst looking to commercialise the technology.


Author
Graham Pitcher

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