The nodes in these systems can be separated by more than one kilometer. Since metal wires dissipate electrical signals as heat when transferring data at high speeds, these systems transfer data via fiber-optic cables. Unfortunately, a lot of energy is wasted in the process of converting electrical data into optical data (and back again) as signals are sent from one node to another.

In a study published today in Nature Photonics, researchers at Columbia Engineering demonstrate an energy-efficient method for transferring larger quantities of data over the fiber-optic cables that connect the nodes. This new technology improves on previous attempts to transmit multiple signals simultaneously over the same fiber-optic cables. Instead of using a different laser to generate each wavelength of light, the new chips require only a single laser to generate hundreds of distinct wavelengths of light that can simultaneously transfer independent streams of data.

A simpler, more energy-efficient method for data transfer

The millimeter-scale system employs a technique called wavelength-division multiplexing (WDM) and devices called Kerr frequency combs that take a single color of light at the input and create many new colors of light at the output. The critical Kerr frequency combs developed by Michal Lipson, Higgins Professor of Electrical Engineering and Professor of Applied Physics, and Alexander Gaeta, David M. Rickey Professor of Applied Physics and Materials Science and Professor of Electrical Engineering, allowed the researchers to send clear signals through separate and precise wavelengths of light, with space in between them.

“We recognized that these devices make ideal sources for optical communications, where one can encode independent information channels on each color of light and propagate them over a single optical fiber,” says senior author Keren Bergman, Charles Batchelor Professor of Electrical Engineering at Columbia Engineering, where she also serves as the faculty director of the Columbia Nano Initiative. This breakthrough could allow systems to transfer exponentially more data without using proportionately more energy.

The team miniaturized all of the optical components onto chips roughly a few millimeters on each edge for generating light, encoded them with electrical data, and then converted the optical data back into an electrical signal at the target node. They devised a novel photonic circuit architecture that allows each channel to be individually encoded with data while having minimal interference with neighboring channels. That means the signals sent in each color of light don’t become muddled and difficult for the receiver to interpret and convert back into electronic data.

“In this way, our approach is much more compact and energy-efficient than comparable approaches,” says the study’s lead author Anthony Rizzo, who conducted this work while a PhD student in the Bergman lab and is now a research scientist at the U.S. Air Force Research Laboratory Information Directorate. “It is also cheaper and easier to scale since the silicon nitride comb generation chips can be fabricated in standard CMOS foundries used to fabricate microelectronics chips rather than in expensive dedicated III-V foundries.”

The compact nature of these chips enables them to directly interface with computer electronics chips, greatly reducing the total energy consumption since the electrical data signals only have to propagate over millimeters of distance rather than tens of centimeters.

Bergman noted, “What this work shows is a viable path towards both dramatically reducing the system energy consumption while simultaneously increasing the computing power by orders of magnitude, allowing artificial intelligence applications to continue to grow at an exponential rate with minimal environmental impact.”

Exciting results pave the way to real-world deployment

In experiments, the researchers managed to transmit 16 gigabits per second per wavelength for 32 distinct wavelengths of light for a total single-fiber bandwidth of 512 Gb/s with less than one bit in error out of one trillion transmitted bits of data. These are incredibly high levels of speed and efficiency. The silicon chip transmitting the data measured just 4 mm x 1 mm, while the chip that received the optical signal and converted it into an electrical signal measured just 3 mm x 1 mm — both smaller than a human fingernail.

“While we used 32 wavelength channels in the proof-of-principle demonstration, our architecture can be scaled to accommodate over 100 channels, which is well within the reach of standard Kerr comb designs,” Rizzo adds.

These chips can be fabricated using the same facilities used to make the microelectronics chips found in a standard consumer laptop or cellphone, providing a straightforward path to volume scaling and real-world deployment.

The next step in this research is to integrate the photonics with chip-scale driving and control electronics to further miniaturize the system.

Planets form in a disk around a newborn star. These ‘proto-planetary’ disks only last a few million years, meaning that a forming planetary system only has this amount of time to finish its formation. However, it is still not clear just how rapidly planet formation begins within these disks. Recent ALMA observations have revealed that many proto-planetary disks have substructures such as gaps and rings, indicating that planets are already forming from the disk. “These previous results motivated us to examine even younger disks around protostars to answer the question, at what stage of star formation do planet forms,” says Nagayoshi Ohashi at Academia Sinica Institute of Astronomy and Astrophysics (ASIAA, Taiwan), who led the team.

The team observed disks around 19 protostars located within about 650 light-years from the Earth. This is the first systematic study to investigate the detailed structure of disks around a large sample of protostars with high angular resolution. The observations clearly show that the disks around protostars are different from more-evolved proto-planetary disks. Among the 19 protostars, rings, and gaps, which are signs of planet formation, were observed only in a few disks. Moreover, the ring structures are less distinct than those seen in the proto-planetary disks.

“We did not expect to see such clear differences between disks around protostars and more-evolved disks,” says Ohashi. John Tobin, a Co-PI of the program at the National Radio Astronomical Observatory (USA) adds “Our results suggest that disks around protostars are not fully ready for planet formation. We believe that the actual formation of the planetary system progresses rapidly in the 100,000 years to 1,000,000 years after star formation begins.”

“One quarter of the global population lives in or downstream from mountainous regions,” said Mohammed Ombadi, first author of the paper published today in Nature. “They are going to be directly affected by this risk.”

Scientists already expect climate change to increase the volume of water falling during extreme events (which typically take place over a few hours to a day), but this study is the first time researchers have looked at whether that extreme precipitation comes as rain or snow. They found that the fraction of water falling as snow decreased in mountainous regions, falling instead as rain — making mountains particularly susceptible to extreme rain hazards. They even put a number to it: For every 1 degree Celsius increase in the global temperature, researchers expect an average of 15% more rain at high elevations.

“This increase in rainfall extremes is not only something that is going to happen from now until the end of the 21^st century — we’re already seeing it,” Ombadi said. “That same rate was also evident in the data from 1950 to 2019. Rainfall extremes in mountains have already been increasing, and will continue to change with that 15% rate.”

While all the mountain ranges in the Northern Hemisphere are seeing the shift from snow to rain, those at greatest risk of extreme rainfall events are the North American Pacific mountain ranges (the Cascades, Sierra Nevada, and coastal ranges from Canada to Southern California), the Himalayas, and high-latitude regions. Researchers are still working to understand why those areas are at higher risk than other mountain ranges such as the Rockies or the Alps.

“We think that North American Pacific mountain ranges are more susceptible to the risk of rainfall extremes than other mountain ranges because a significant portion of snowfall in this region typically occurs at temperatures just below zero degrees Celsius,” Ombadi said. “The slightest change in air temperature will shift this snowfall to rainfall. This is unlike other mountain ranges where snowfall may occur at very low temperatures below zero degrees.”

Ombadi hopes that fellow climate scientists will incorporate the distinction between snowfall and rainfall to improve global climate models, and that civil engineers and planners will use the data to better prepare for intense rain events.

“We need to factor these results into how we design and build the infrastructure in these mountainous regions, so that they can withstand the negative consequences of increases in rainfall extremes,” Ombadi said.

Meanwhile, countries continue efforts to meet targets established by the Paris Agreement that would limit global warming to less than 2 degrees Celsius above pre-industrial levels.

“Our findings revealed a linear relationship between the level of warming and the increase in extreme rainfall: For instance, 1 degree of warming causes 15% more rain, while 3 degrees leads to a 45% increase in rainfall,” Ombadi said. “There are many technologies in progress that could help us reduce greenhouse gas emissions and how much the planet warms. To me, this study shows the need to invest in those clean solutions, and also start preparing for the consequences of warming now.”

This work was funded by the DOE Office of Science Biological and Environmental Research program.

To expand their X-ray spectroscopy observations to liquids, the researchers had to design an apparatus capable of producing a liquid jet with a diameter of less than one micrometre in a vacuum. This was essential because if the jet were any wider, it would absorb some of the X-rays used to measure it.

Molecular pioneer in biochemistry

Using the new method, the researchers were able to gain insights into the processes that led to the emergence of life on Earth. Many scientists assume that urea played a pivotal role here. It is one of the simplest molecules containing both carbon and nitrogen. What’s more, it’s highly likely that urea was present even when the Earth was very young, something that was also suggested by a famous experiment done in the 1950s: American scientist Stanley Miller concocted a mixture of those gases believed to have made up the planet’s primordial atmosphere and exposed it to the conditions of a thunderstorm. This produced a series of molecules, one of which was urea.

According to current theories, the urea could have become enriched in warm puddles — commonly called primordial soup — on the then lifeless Earth. As the water in this soup evaporated, the concentration of urea increased. Through exposure to ionising radiation such as cosmic rays, it’s possible that this concentrated urea produced malonic acid over multiple synthesis steps. In turn, this may have created the building blocks of RNA and DNA.

Why this exact reaction tool place

Using their new method, the researchers from ETH Zurich and the University of Geneva investigated the first step in this long series of chemical reactions to find out how a concentrated urea solution behaves when exposed to ionising radiation.

It’s important to know that the urea molecules in a concentrated urea solution group themselves into pairs, or what are known as dimers. As the researchers have now been able to show, ionising radiation causes a hydrogen atom within each of these dimers to move from one urea molecule to the other. This turns one urea molecule into a protonated urea molecule, and the other into a urea radical. The latter is highly chemically reactive — so reactive, in fact, that it’s very likely to react with other molecules, thereby also forming malonic acid.

The researchers also managed to show that this transfer of a hydrogen atom happens extremely quickly, taking only around 150 femtoseconds, or 150 quadrillionths of a second. “That’s so fast that this reaction preempts all other reactions that might theoretically also take place,” Wörner says. “This explains why concentrated urea solutions produce urea radicals rather than hosting other reactions that would produce other molecules.”

Reactions in liquids are highly relevant

In the future, Wörner and his colleagues want to examine the next steps that lead to the formation of malonic acid. They hope this will help them to understand the origins of life on Earth.

As for their new method, it can also generally be used to examine the precise sequence of chemical reactions in liquids. “A whole host of important chemical reactions take place in liquids — not just all biochemical processes in the human body, but also a great many chemical syntheses relevant to industry,” Wörner says. “This is why it’s so important that we have now expanded the scope of X-ray spectroscopy at high temporal resolution to include reactions in liquids.”

The researchers from ETH Zurich and the University of Geneva were assisted in this work by colleagues from Deutsches Elektronen-Synchrotron DESY in Hamburg, who performed calculations required to interpret measurement data.