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Li-Fi-like System Would Bring 100-Gbps Speeds Straight to Your Computer

System sends light signals from the optical fiber fiber through the air to your computer

3 min read
Li-Fi-like System Would Bring 100-Gbps Speeds Straight to Your Computer
Photo: University of Oxford

The light that zips data across the Internet’s backbone used to stop a long way from the data’s final destination. Now it goes all the way to your home. Why not go the last step and take the light all the way to the computer or TV, projecting it through the air over the last few meters and only converting it to an electronic signal at the end? Oxford University is doing just that with a system that takes light from the fiber, amplifies it, and beams it across a room to deliver data at more than 100 gigabits per second.

Such indoor optical wireless probably wouldn’t replace Wi-Fi, says Ariel Gomez, a Ph.D. student in photonics at Oxford University who describes the system inIEEE Photonics Technology Letters. But with a potential for data rates of 3 terabits per second and up, it could certainly find its uses. Wi-Fi, by contrast, tops out at about 7 Gb/s. And with light, there’s no worry about sticking to a limited set of radio frequencies. “If you’re in the optical window, you have virtually unlimited bandwidth and unlicensed spectrum,” Gomez says.

With a 60° field of view, the team was able to transmit with an aggregate bandwidth of 224 gigabits per second.

To accomplish this, they’d install a base station on the ceiling of a room, which would project the light toward the computer and also receive data heading out from the computer to the Internet.

The trick, of course, is getting the light beam exactly where it needs to go. An optical fiber makes for a target that’s only 8 or 9 micrometers in diameter, after all. The team, which also included researchers from University College, London, accomplished this using so-called holographic beam steering at both the transmitter and receiver ends. These use an array of liquid crystals to create a programmable diffraction grating that reflects the light in the desired direction. The device is similar to that used in projectors, says Dominic O’Brien, a photonics engineer at Oxford who directed the work.

It’s important to use transceivers with a wide field of view to make the alignment task easier, particularly because the device relies on wavelength division multiplexing, which splits the signal into slightly different colors of light. Like a prism, the diffraction grating of the beam steerer bends each wavelength a different amount. With a 60° field of view, the team was able to transmit six different wavelengths, each at 37.4 Gb/s, for an aggregate bandwidth of 224 Gb/s. With a 36° field of view, they managed only three channels, for 112 Gb/s.

The system requires a direct line of sight, and for now the receiver must be in a fixed position. The next step, O’Brien says, is to develop a tracking and location system so that a user could place a laptop at a random spot on a table and have the system find it and create a link.

Brien is a member of the Ultra-Parallel Visible Light Communications project, with colleagues at the Universities of Edinburgh, Strathclyde, St. Andrews, and Cambridge. One of their goals is to develop LiFi, which uses the light that’s also illuminating a room as a way to send data signals. He says LiFi usually refers to schemes based on visible wavelengths of light, whereas this system relies on infrared light at 1550 nm, which is used in telecommunications.

All these technologies—Wi-Fi, LiFi, optical wireless—may wind up being part of how people link devices to the Internet. “The world of communications is a world where everybody always wants more bandwidth,” O’Brien says.

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3 Ways 3D Chip Tech Is Upending Computing

AMD, Graphcore, and Intel show why the industry’s leading edge is going vertical

8 min read
Vertical
A stack of 3 images.  One of a chip, another is a group of chips and a single grey chip.
Intel; Graphcore; AMD
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A crop of high-performance processors is showing that the new direction for continuing Moore’s Law is all about up. Each generation of processor needs to perform better than the last, and, at its most basic, that means integrating more logic onto the silicon. But there are two problems: One is that our ability to shrink transistors and the logic and memory blocks they make up is slowing down. The other is that chips have reached their size limits. Photolithography tools can pattern only an area of about 850 square millimeters, which is about the size of a top-of-the-line Nvidia GPU.

For a few years now, developers of systems-on-chips have begun to break up their ever-larger designs into smaller chiplets and link them together inside the same package to effectively increase the silicon area, among other advantages. In CPUs, these links have mostly been so-called 2.5D, where the chiplets are set beside each other and connected using short, dense interconnects. Momentum for this type of integration will likely only grow now that most of the major manufacturers have agreed on a 2.5D chiplet-to-chiplet communications standard.

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