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This Chip Could Replace a Thousand Lasers

Frequency combs are key to optical chips that could cut Internet power consumption

2 min read
Illustration of a square shape with a yellow ring on top and red lines in a pattern rising from the circle in small, then large sections.

This is an illustration of a microring resonator with an integrated heater element, which is key to generating the frequency comb. The red graph represents the light pulse circulating inside the microring resonator.

Nature Photonics

A record-breaking optical chip can transmit 1.8 petabits—1.8 million gigabits—per second, roughly twice as much traffic as transmitted per second over the entire world's Internet, a new study finds.

Previous research transmitted up to 10.66 petabits per second over fiber optics. However, these experiments relied on bulky electronics. A compact microchip-based strategy could enable mass production and result in smaller footprints, lower costs, and lower energy consumption. Until now, the fastest single optical microchip supported data rates of 661 terabits—661,000 gigabits—per second.

The new chip uses the light from a single infrared laser to create a rainbow spectrum of many colors. All the resulting frequencies of light are a fixed specific frequency distance from one another, a bit like the teeth of the comb, which is why the device is called a frequency comb. Each frequency can be isolated and have such properties as its amplitude modulated to carry data. The frequencies can then be collected together and transmitted simultaneously over fiber optics.

“Several groups worldwide have shown that frequency combs can be used for data transmission instead of using individual lasers,” says study senior author Leif Katsuo Oxenløwe, an optical communications researcher at the Technical University of Denmark.

The new microchip emits light roughly 1,530 to 1,610 nanometers in wavelength. These fall into the C and L bands of telecommunications frequencies, two of five wavelength bands where optical fibers experience minimal signal loss.

In experiments, the scientists achieved 1.84 petabits per second over a 7.9-kilometer-long optical fiber using 223 wavelength channels. “This is the first time it is investigated just how much data a single frequency comb can carry,” Oxenløwe says.

Using conventional equipment, this data rate would require about 1,000 lasers, the researchers say. The new microchip could therefore help significantly reduce Internet power consumption. “You could save a thousand lasers out of your energy budget,” Oxenløwe says.

In addition, a computational model the scientists developed to examine the potential of frequency combs suggests that a single chip could achieve a data rate of up to 100 petabits per second if given a cable with thousands of fibers. “You can already today buy cables with thousands of fibers in them to transport large quantities of data around in data centers, so scaling to such numbers is actually realistic,” Oxenløwe says.

The researchers say they accomplish this staggering data rate by dividing one frequency comb into many copies and optically amplifying their signals. “The power and potential of frequency combs is thus far greater than I think most comb enthusiasts even dared to dream of,” Oxenløwe says.

Future research can integrate components such as the laser, data modulators, and amplifiers onto the optical chip, Oxenløwe says.

The scientists detailed their findings 20 October in the journal Nature Photonics.

The Conversation (0)

Metamaterials Could Solve One of 6G’s Big Problems

There’s plenty of bandwidth available if we use reconfigurable intelligent surfaces

12 min read
An illustration depicting cellphone users at street level in a city, with wireless signals reaching them via reflecting surfaces.

Ground level in a typical urban canyon, shielded by tall buildings, will be inaccessible to some 6G frequencies. Deft placement of reconfigurable intelligent surfaces [yellow] will enable the signals to pervade these areas.

Chris Philpot

For all the tumultuous revolution in wireless technology over the past several decades, there have been a couple of constants. One is the overcrowding of radio bands, and the other is the move to escape that congestion by exploiting higher and higher frequencies. And today, as engineers roll out 5G and plan for 6G wireless, they find themselves at a crossroads: After years of designing superefficient transmitters and receivers, and of compensating for the signal losses at the end points of a radio channel, they’re beginning to realize that they are approaching the practical limits of transmitter and receiver efficiency. From now on, to get high performance as we go to higher frequencies, we will need to engineer the wireless channel itself. But how can we possibly engineer and control a wireless environment, which is determined by a host of factors, many of them random and therefore unpredictable?

Perhaps the most promising solution, right now, is to use reconfigurable intelligent surfaces. These are planar structures typically ranging in size from about 100 square centimeters to about 5 square meters or more, depending on the frequency and other factors. These surfaces use advanced substances called metamaterials to reflect and refract electromagnetic waves. Thin two-dimensional metamaterials, known as metasurfaces, can be designed to sense the local electromagnetic environment and tune the wave’s key properties, such as its amplitude, phase, and polarization, as the wave is reflected or refracted by the surface. So as the waves fall on such a surface, it can alter the incident waves’ direction so as to strengthen the channel. In fact, these metasurfaces can be programmed to make these changes dynamically, reconfiguring the signal in real time in response to changes in the wireless channel. Think of reconfigurable intelligent surfaces as the next evolution of the repeater concept.

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