Stanford physics innovation paves way for computing with pho
Source: Jose Fermoso
Engineers at Stanford University have built a device they say could lead to the eventual development of computers that use photons sent via laser for power, as opposed to sending electrons over circuits.
A computer that could use light to transmit data may be up to 1,000 times faster than the fastest electricity-powered computer and may also provide about 100 times improvement in power efficiency, said doctoral student Alexander Yukio Piggott. He's one of the lead authors of the Stanford paper recently published about the project in the open-access Scientific Reports publication.
Higher amounts of data can transferred through light down a single optical fiber, at about 70 terabits per second. That level of data is "absolutely insane" when compared to a current data transfer-speed record of about 10 gigabits per second, Piggott told me in an interview.
These projected figures are based on a number of assumptions: The transfer-speed levels of current, long-range fiber optic networks and on the use of optimal versions of other parts that go into microchips, such as a light detector, and the quality of the algorithm used in designing the chips.
The device, prototyped at Stanford, transmits laser light at microscopic levels of connectivity between chips and between parts inside chips. Major companies like IBM and other universities like Cornell and U.C. Berkeley are also exploring the technology.
A recent KPMG global survey of business leaders in the semiconductor industry said optoelectronics is one of the top three sectors with the "highest growth opportunity" in 2015. Optoelectronics devices have electrical and optical sensors that transmit, detect and control light between them. Some experts are predicting there will be a light-powered computer in the enterprise market in the next five years.
Optical links small enough to replace microscopic electrical ones are relatively new but optical links have replaced electrical links for decades. Fiber optics, for example, connect individual servers and supercomputers across oceans.
Jelena Vuckovic, professor of electrical engineering at Stanford, and Piggott, one of her Ph.D. students, are the lead authors of the paper describing the finding. The paper also includes work from four other members of Vuckovic's lab.
The key part of the Stanford device, according to photonics expert and UCLA professor Chee Wei Wang, is the software used to make it. Wang says the software has an algorithm that allows scientists to design the exact size of laser light needed to transmit data between microchips. The algorithm reverse-engineers a solution ― or rather, determines the size of the light ― based on the size of the wavelengths of fiber optic networks.
Stanford's algorithm can allow scientists to design small optical components of at least 10 microns across, according to Piggott. Algorithms that are used to design optical devices have only been discovered in the past two to three years.
The software was mostly written by a former Ph.D. student in the group named Jesse Lu, Piggott told me. It took Lu and company 18 months to write, debug and test the system.
Stanford's software also designs the parts that connect optical microchips, including a sequence called the "optical link." This link includes a microscopic chip that looks like a 3-D bar code, a modulator that changes the laser light to imprint data, optical fiber through which the light travels, and a light detector. Data is transferred when light is sent through the gaps within the bar code and splits into two wavelengths to other chips.
The reduction of power consumption through light-powered computers is potentially significant.
The U.S. Environmental Protection Agency in 2007 found data centers use 1.5 percent of all U.S. electricity production. According to Piggott, more than 80 percent of power is consumed by sending data down electrical wires ― not by powering the computers themselves ― so replacing wires with optical links could significantly reduce electricity consumption.
Electrically powered silicon chips may need to be replaced because of stability issues as miniturization continues. Chips smaller than seven nanometers may not be able to maintain a reliable on-and-off state, some experts said. Because the smallest electrical microchips today are 22 nanometers wide, Moore's Law (which states that the number of transistors on an chip will double every two years) may soon force companies to look to new technologies for speed and capacity advantages.
Vuckovic and Piggott both say mass-producing photonic chips will be challenging because of compatibility issues between transistor-based chips and photonic devices. This means large companies with the financial ability to invest in long-term technology, like IBM and Intel, are the most likely to develop and produce photonic chips in the near future.
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