Improvements to two optical modulators are seen as a major step toward a major goal in silicon photonics: enabling microprocessors to use light instead of electrical signals to communicate with transistors on a chip.
Fig 1:A silicon wafer containing the photonic-electronic microchips.
The pair of optical modulators was made at the University of Colorado at Boulder, MIT and Micron Technology Inc., and the team said that the work could allow for the trajectory of exponential improvement in microprocessors that began nearly half a century ago — known as Moore's Law — to continue well into the future, allowing for increasingly faster electronics, from supercomputers to laptops to smartphones.
The research team, led by CU-Boulder researcher Milos Popovic, an assistant professor of electrical, computer and energy engineering, developed a new light-based technique for microprocessors. He and his colleagues created two different optical modulators — structures that detect electrical signals and translate them into optical waves — that can be fabricated using standard industrial processes for microprocessors.
In 1965, Intel co-founder Gordon Moore predicted that the size of transistors used in microprocessors could be shrunk by half about every two years for the same production cost, allowing twice as many to be placed on the same-sized silicon chip. The net effect would be a doubling of computing speed every couple of years, and his projection held true for more than 40 years.
Fig 1: A silicon wafer containing the photonic-electronic microchips designed by the research team, which includes scientists from CU-Boulder, MIT, Micron and UC Berkeley. Introducing photonics into electronic microprocessors could extend Moore's Law well into the future.
While transistors continue to get smaller, halving their size no longer leads to a doubling of computing speed. The limiting factor is the power needed to keep the microprocessors running. The vast amount of electricity required to flip on and off tiny, densely packed transistors causes excessive heat buildup.
"The transistors will keep shrinking, and they'll be able to continue giving you more and more computing performance," Popovic said. "But in order to be able to actually take advantage of that, you need to enable energy-efficient communication links."
Another limitation with microelectronics is that positioning electrical wires carrying data too closely can result in crosstalk between the wires.
In the past half-dozen years, microprocessor manufacturers such as Intel have continued increasing computing speed by packing more than one microprocessor into a single chip, creating multiple "cores." But that technique is limited by the amount of communication that becomes necessary between the microprocessors, requiring hefty electricity consumption.
Using lightwaves instead of electrical wires could eliminate these limitations and extend Moore's Law into the future, Popovic said.
To make optical communication an economically viable option for microprocessors, the photonic technology must be fabricated in the same foundries that are used to create the microprocessors. Photonics must be integrated side-by-side with the electronics to get buy-in from the microprocessor industry, Popovic said.
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