NASA to demonstrate communications via laser beam

ScienceDaily (Sep. 24, 2011) — It currently takes 90 minutes to transmit high-resolution images from Mars, but NASA would like to dramatically reduce that time to just minutes. A new optical communications system that NASA plans to demonstrate in 2016 will lead the way and even allow the streaming of high-definition video from distances beyond the Moon.

This dramatically enhanced transmission speed will be demonstrated by the Laser Communications Relay Demonstration (LCRD), one of three projects selected by NASA's Office of the Chief Technologist (OCT) for a trial run. To be developed by a team led by engineers at the NASA Goddard Space Flight Center in Greenbelt, Md., LCRD is expected to fly as a hosted payload on a commercial communications satellite developed by Space Systems/Loral, of Palo Alto, Calif.

"We want to take NASA's communications capabilities to the next level," said LCRD Principal Investigator Dave Israel, who is leading a multi-organizational team that includes NASA's Jet Propulsion Laboratory, Pasadena, Calif. and Lincoln Laboratory at the Massachusetts Institute of Technology, Cambridge, Mass. Although NASA has developed higher data-rate radio frequency systems, data-compression, and other techniques to boost the amount of data that its current systems can handle, the Agency's capabilities will not keep pace with the projected data needs of advanced instruments and future human exploration, Israel added.

"Just as the home Internet user hit the wall with dial-up, NASA is approaching the limit of what its existing communications network can handle," he said.

The solution is to augment NASA's legacy radio-based network, which includes a fleet of tracking and data relay satellites and a network of ground stations, with optical systems, which could increase data rates by anywhere from 10 to 100 times. "This transition will take several years to complete, but the eventual payback will be very large increases in the amount of data we can transmit, both downlink and uplink, especially to distant destinations in the solar system and beyond," said James Reuther, director of OCT's Crosscutting Technology Demonstrations Division.

First Step

The LCRD is the next step in that direction, Israel said, likening the emerging capability to land-based fiber-optic systems, such as Verizon's FiOS network. "In a sense, we're moving FiOS to space."

To demonstrate the new capability, the Goddard team will encode digital data and transmit the information via laser light from specially equipped ground stations to an experimental payload hosted on the commercial communications satellite.

The payload will include telescopes, lasers, mirrors, detectors, a pointing and tracking system, control electronics, and two different types of modems. One modem is ideal for communicating with deep space missions or tiny, low-power smallsats operating in low-Earth orbit. The other can handle much higher data rates, particularly from Earth-orbiting spacecraft, including the International Space Station. "With the higher-speed modem type, future systems could support data rates of tens of gigabits per second," Israel said.

Once the payload receives the data, it would then relay it back to ground stations now scheduled to operate in Hawaii and Southern California.

The multiple ground stations are important to demonstrating a fully operational system, Israel said. Cloud cover and turbulent atmospheric conditions impede laser communications, requiring a clear line of sight between the transmitter and receiver. If bad weather prevents a signal from being sent or received at one location, the network could hand over the responsibility to one of the other ground stations or store it for later retransmission.

The demonstration is expected to run two to three years.

Follow-On to LADEE Experiment

The project isn't NASA's first foray into laser communications. Goddard engineers are now developing a laser communications payload for NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE), which the Agency plans to launch in 2013 to characterize the Moon's wisp-thin atmosphere and dust environment. The main goal of the LADEE experiment is proving fundamental concepts of laser-based communications and transferring up to 622 megabits per second, which is about five times the current state-of-the-art from lunar distances.

However, the LADEE payload, called the Lunar Laser Communications Demonstration (LLCD), is equipped with only one modem, the lower-speed model best suited for deep space communications. In addition, LADEE is a short-duration mission. LLCD is expected to operate for only 16 days of the LADEE mission, not enough time to demonstrate a fully operational laser-communications network, Israel said.

"What we're trying to do is get ahead of the curve," Israel said. "We want to get to the point where communications is no longer a constraint on scientists who want to gather more data, but are worried about getting their data back from space."

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by NASA/Goddard Space Flight Center.

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NASA to demonstrate communications via laser beam

ScienceDaily (Sep. 24, 2011) — It currently takes 90 minutes to transmit high-resolution images from Mars, but NASA would like to dramatically reduce that time to just minutes. A new optical communications system that NASA plans to demonstrate in 2016 will lead the way and even allow the streaming of high-definition video from distances beyond the Moon.

This dramatically enhanced transmission speed will be demonstrated by the Laser Communications Relay Demonstration (LCRD), one of three projects selected by NASA's Office of the Chief Technologist (OCT) for a trial run. To be developed by a team led by engineers at the NASA Goddard Space Flight Center in Greenbelt, Md., LCRD is expected to fly as a hosted payload on a commercial communications satellite developed by Space Systems/Loral, of Palo Alto, Calif.

"We want to take NASA's communications capabilities to the next level," said LCRD Principal Investigator Dave Israel, who is leading a multi-organizational team that includes NASA's Jet Propulsion Laboratory, Pasadena, Calif. and Lincoln Laboratory at the Massachusetts Institute of Technology, Cambridge, Mass. Although NASA has developed higher data-rate radio frequency systems, data-compression, and other techniques to boost the amount of data that its current systems can handle, the Agency's capabilities will not keep pace with the projected data needs of advanced instruments and future human exploration, Israel added.

"Just as the home Internet user hit the wall with dial-up, NASA is approaching the limit of what its existing communications network can handle," he said.

The solution is to augment NASA's legacy radio-based network, which includes a fleet of tracking and data relay satellites and a network of ground stations, with optical systems, which could increase data rates by anywhere from 10 to 100 times. "This transition will take several years to complete, but the eventual payback will be very large increases in the amount of data we can transmit, both downlink and uplink, especially to distant destinations in the solar system and beyond," said James Reuther, director of OCT's Crosscutting Technology Demonstrations Division.

First Step

The LCRD is the next step in that direction, Israel said, likening the emerging capability to land-based fiber-optic systems, such as Verizon's FiOS network. "In a sense, we're moving FiOS to space."

To demonstrate the new capability, the Goddard team will encode digital data and transmit the information via laser light from specially equipped ground stations to an experimental payload hosted on the commercial communications satellite.

The payload will include telescopes, lasers, mirrors, detectors, a pointing and tracking system, control electronics, and two different types of modems. One modem is ideal for communicating with deep space missions or tiny, low-power smallsats operating in low-Earth orbit. The other can handle much higher data rates, particularly from Earth-orbiting spacecraft, including the International Space Station. "With the higher-speed modem type, future systems could support data rates of tens of gigabits per second," Israel said.

Once the payload receives the data, it would then relay it back to ground stations now scheduled to operate in Hawaii and Southern California.

The multiple ground stations are important to demonstrating a fully operational system, Israel said. Cloud cover and turbulent atmospheric conditions impede laser communications, requiring a clear line of sight between the transmitter and receiver. If bad weather prevents a signal from being sent or received at one location, the network could hand over the responsibility to one of the other ground stations or store it for later retransmission.

The demonstration is expected to run two to three years.

Follow-On to LADEE Experiment

The project isn't NASA's first foray into laser communications. Goddard engineers are now developing a laser communications payload for NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE), which the Agency plans to launch in 2013 to characterize the Moon's wisp-thin atmosphere and dust environment. The main goal of the LADEE experiment is proving fundamental concepts of laser-based communications and transferring up to 622 megabits per second, which is about five times the current state-of-the-art from lunar distances.

However, the LADEE payload, called the Lunar Laser Communications Demonstration (LLCD), is equipped with only one modem, the lower-speed model best suited for deep space communications. In addition, LADEE is a short-duration mission. LLCD is expected to operate for only 16 days of the LADEE mission, not enough time to demonstrate a fully operational laser-communications network, Israel said.

"What we're trying to do is get ahead of the curve," Israel said. "We want to get to the point where communications is no longer a constraint on scientists who want to gather more data, but are worried about getting their data back from space."

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by NASA/Goddard Space Flight Center.

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Quantum cryptography: Perfect eavesdropper illustrates overlooked loophole in secure communications technology

ScienceDaily (June 14, 2011) — Quantum key distribution (QKD) is an advanced tool for secure computer-based interactions, providing confidential communication between two remote parties by enabling them to construct a shared secret key during the course of their conversation.

QKD is perfectly secure in principle, but researchers have long been aware that loopholes may arise when QKD is put into practice. Now, for the first time, a team of researchers at the Centre for Quantum Technologies (CQT) at the National University of Singapore, the Norwegian University of Science and Technology (NTNU) and the University Graduate Center (UNIK) in Norway have created and operated a "perfect eavesdropper" for QKD that exploits just such a loophole in a typical QKD setup. As reported in the most recent issue of Nature Communications, this eavesdropper enabled researchers to obtain an entire shared secret key without alerting either of the legitimate parties that there had been a security breach. The results highlight the importance of identifying imperfections in the implementation of QKD as a first step towards fixing them.

Cryptography has traditionally relied on mathematical conjectures and thus may always be prone to being "cracked" by a clever mathematician who can figure out how to efficiently solve a mathematical puzzle, aided by the continual development of ever-faster computers. Quantum cryptography, however, relies on the laws of physics and should be infinitely more difficult to crack than traditional approaches. While there has been much discussion of the technological vulnerabilities in quantum cryptography that might jeopardize this promise, there have been no successful full field-implemented hacks of QKD security -- until now.

"Quantum key distribution has matured into a true competitor to classical key distribution. This attack highlights where we need to pay attention to ensure the security of this technology," says Christian Kurtsiefer, a professor at the Centre for Quantum Technologies at the National University of Singapore.

In the setup that was tested, researchers at the three institutions demonstrated their eavesdropping attack in realistic conditions over a 290-m fibre link between a transmitter called "Alice" and a receiver called "Bob." Alice transmits light to Bob one photon at a time, and the two build up their secret key by measuring properties of the photons. During multiple QKD sessions over a few hours, the perfect eavesdropper "Eve" obtained the same "secret" key as Bob, while the usual parameters monitored in the QKD exchange were not disturbed -- meaning that Eve remained undetected.

The researchers were able to circumvent the quantum principles that in theory provide QKD its strong security by making the photon detectors in Bob behave in a classical way. The detectors were blinded, essentially overriding the system's ability to detect a breach of security. Furthermore, this technological imperfection in QKD security was breached using off-the-shelf components.

"This confirms that non-idealities in the physical implementations of QKD can be fully and practically exploitable, and must be given increased scrutiny if quantum cryptography is to become highly secure," says Vadim Makarov, a postdoctoral researcher at the University Graduate Center in Kjeller, Norway. "We can not simply delegate the burden of keeping a secret to the laws of quantum physics; we need to carefully investigate the specific devices involved," says Kurtsiefer.

The open publication of how the "perfect eavesdropper" was built has already enabled this particular loophole in QKD to be closed. "I am sure there are other problems that might show that a theoretical security analysis is not necessarily exactly the same as a real-world situation," says Ilja Gerhardt, currently a visiting scholar at the University of British Columbia in Vancouver, Canada. "But this is the usual game in cryptography -- a secure communications system is created and others try to break into it. In the end this makes the different approaches better."

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Centre for Quantum Technologies at the National University of Singapore.

Journal Reference:

Ilja Gerhardt, Qin Liu, Antía Lamas-Linares, Johannes Skaar, Christian Kurtsiefer, Vadim Makarov. Full-field implementation of a perfect eavesdropper on a quantum cryptography system. Nature Communications, 2011; 2: 349 DOI: 10.1038/ncomms1348

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Quantum cryptography: Perfect eavesdropper illustrates overlooked loophole in secure communications technology

ScienceDaily (June 14, 2011) — Quantum key distribution (QKD) is an advanced tool for secure computer-based interactions, providing confidential communication between two remote parties by enabling them to construct a shared secret key during the course of their conversation.

QKD is perfectly secure in principle, but researchers have long been aware that loopholes may arise when QKD is put into practice. Now, for the first time, a team of researchers at the Centre for Quantum Technologies (CQT) at the National University of Singapore, the Norwegian University of Science and Technology (NTNU) and the University Graduate Center (UNIK) in Norway have created and operated a "perfect eavesdropper" for QKD that exploits just such a loophole in a typical QKD setup. As reported in the most recent issue of Nature Communications, this eavesdropper enabled researchers to obtain an entire shared secret key without alerting either of the legitimate parties that there had been a security breach. The results highlight the importance of identifying imperfections in the implementation of QKD as a first step towards fixing them.

Cryptography has traditionally relied on mathematical conjectures and thus may always be prone to being "cracked" by a clever mathematician who can figure out how to efficiently solve a mathematical puzzle, aided by the continual development of ever-faster computers. Quantum cryptography, however, relies on the laws of physics and should be infinitely more difficult to crack than traditional approaches. While there has been much discussion of the technological vulnerabilities in quantum cryptography that might jeopardize this promise, there have been no successful full field-implemented hacks of QKD security -- until now.

"Quantum key distribution has matured into a true competitor to classical key distribution. This attack highlights where we need to pay attention to ensure the security of this technology," says Christian Kurtsiefer, a professor at the Centre for Quantum Technologies at the National University of Singapore.

In the setup that was tested, researchers at the three institutions demonstrated their eavesdropping attack in realistic conditions over a 290-m fibre link between a transmitter called "Alice" and a receiver called "Bob." Alice transmits light to Bob one photon at a time, and the two build up their secret key by measuring properties of the photons. During multiple QKD sessions over a few hours, the perfect eavesdropper "Eve" obtained the same "secret" key as Bob, while the usual parameters monitored in the QKD exchange were not disturbed -- meaning that Eve remained undetected.

The researchers were able to circumvent the quantum principles that in theory provide QKD its strong security by making the photon detectors in Bob behave in a classical way. The detectors were blinded, essentially overriding the system's ability to detect a breach of security. Furthermore, this technological imperfection in QKD security was breached using off-the-shelf components.

"This confirms that non-idealities in the physical implementations of QKD can be fully and practically exploitable, and must be given increased scrutiny if quantum cryptography is to become highly secure," says Vadim Makarov, a postdoctoral researcher at the University Graduate Center in Kjeller, Norway. "We can not simply delegate the burden of keeping a secret to the laws of quantum physics; we need to carefully investigate the specific devices involved," says Kurtsiefer.

The open publication of how the "perfect eavesdropper" was built has already enabled this particular loophole in QKD to be closed. "I am sure there are other problems that might show that a theoretical security analysis is not necessarily exactly the same as a real-world situation," says Ilja Gerhardt, currently a visiting scholar at the University of British Columbia in Vancouver, Canada. "But this is the usual game in cryptography -- a secure communications system is created and others try to break into it. In the end this makes the different approaches better."

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Centre for Quantum Technologies at the National University of Singapore.

Journal Reference:

Ilja Gerhardt, Qin Liu, Antía Lamas-Linares, Johannes Skaar, Christian Kurtsiefer, Vadim Makarov. Full-field implementation of a perfect eavesdropper on a quantum cryptography system. Nature Communications, 2011; 2: 349 DOI: 10.1038/ncomms1348

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Toward optical computing in handheld electronics: Graphene optical modulators could lead to ultrafast communications

ScienceDaily (May 9, 2011) — Scientists at the University of California, Berkeley, have demonstrated a new technology for graphene that could break the current speed limits in digital communications.

The team of researchers, led by UC Berkeley engineering professor Xiang Zhang, built a tiny optical device that uses graphene, a one-atom-thick layer of crystallized carbon, to switch light on and off. This switching ability is the fundamental characteristic of a network modulator, which controls the speed at which data packets are transmitted. The faster the data pulses are sent out, the greater the volume of information that can be sent. Graphene-based modulators could soon allow consumers to stream full-length, high-definition, 3-D movies onto a smartphone in a matter of seconds, the researchers said.

"This is the world's smallest optical modulator, and the modulator in data communications is the heart of speed control," said Zhang, who directs a National Science Foundation (NSF) Nanoscale Science and Engineering Center at UC Berkeley. "Graphene enables us to make modulators that are incredibly compact and that potentially perform at speeds up to ten times faster than current technology allows. This new technology will significantly enhance our capabilities in ultrafast optical communication and computing."

In this latest work, described in the May 8 advanced online publication of the journal Nature, researchers were able to tune the graphene electrically to absorb light in wavelengths used in data communication. This advance adds yet another advantage to graphene, which has gained a reputation as a wonder material since 2004 when it was first extracted from graphite, the same element in pencil lead. That achievement earned University of Manchester scientists Andre Geim and Konstantin Novoselov the Nobel Prize in Physics last year.

Zhang worked with fellow faculty member Feng Wang, an assistant professor of physics and head of the Ultrafast Nano-Optics Group at UC Berkeley. Both Zhang and Wang are faculty scientists at Lawrence Berkeley National Laboratory's Materials Science Division.

"The impact of this technology will be far-reaching," said Wang. "In addition to high-speed operations, graphene-based modulators could lead to unconventional applications due to graphene's flexibility and ease in integration with different kinds of materials. Graphene can also be used to modulate new frequency ranges, such as mid-infrared light, that are widely used in molecular sensing."

Graphene is the thinnest, strongest crystalline material yet known. It can be stretched like rubber, and it has the added benefit of being an excellent conductor of heat and electricity. This last quality of graphene makes it a particularly attractive material for electronics.

"Graphene is compatible with silicon technology and is very cheap to make," said Ming Liu, post-doctoral researcher in Zhang's lab and co-lead author of the study. "Researchers in Korea last year have already produced 30-inch sheets of it. Moreover, very little graphene is required for use as a modulator. The graphite in a pencil can provide enough graphene to fabricate 1 billion optical modulators."

It is the behavior of photons and electrons in graphene that first caught the attention of the UC Berkeley researchers.

The researchers found that the energy of the electrons, referred to as its Fermi level, can be easily altered depending upon the voltage applied to the material. The graphene's Fermi level in turn determines if the light is absorbed or not.

When a sufficient negative voltage is applied, electrons are drawn out of the graphene and are no longer available to absorb photons. The light is "switched on" because the graphene becomes totally transparent as the photons pass through.

Graphene is also transparent at certain positive voltages because, in that situation, the electrons become packed so tightly that they cannot absorb the photons.

The researchers found a sweet spot in the middle where there is just enough voltage applied so the electrons can prevent the photons from passing, effectively switching the light "off."

"If graphene were a hallway, and electrons were people, you could say that, when the hall is empty, there's no one around to stop the photons," said Xiaobo Yin, co-lead author of the Nature paper and a research scientist in Zhang's lab. "In the other extreme, when the hall is too crowded, people can't move and are ineffective in blocking the photons. It's in between these two scenarios that the electrons are allowed to interact with and absorb the photons, and the graphene becomes opaque."

In their experiment, the researchers layered graphene on top of a silicon waveguide to fabricate optical modulators. The researchers were able to achieve a modulation speed of 1 gigahertz, but they noted that the speed could theoretically reach as high as 500 gigahertz for a single modulator.

While components based upon optics have many advantages over those that use electricity, including the ability to carry denser packets of data more quickly, attempts to create optical interconnects that fit neatly onto a computer chip have been hampered by the relatively large amount of space required in photonics.

Light waves are less agile in tight spaces than their electrical counterparts, the researchers noted, so photon-based applications have been primarily confined to large-scale devices, such as fiber optic lines.

"Electrons can easily make an L-shaped turn because the wavelengths in which they operate are small," said Zhang. "Light wavelengths are generally bigger, so they need more space to maneuver. It's like turning a long, stretch limo instead of a motorcycle around a corner. That's why optics require bulky mirrors to control their movements. Scaling down the optical device also makes it faster because the single atomic layer of graphene can significantly reduce the capacitance -- the ability to hold an electric charge -- which often hinders device speed."

Graphene-based modulators could overcome the space barrier of optical devices, the researchers said. They successfully shrunk a graphene-based optical modulator down to a relatively tiny 25 square microns, a size roughly 400 times smaller than a human hair. The footprint of a typical commercial modulator can be as large as a few square millimeters.

Even at such a small size, graphene packs a punch in bandwidth capability. Graphene can absorb a broad spectrum of light, ranging over thousands of nanometers from ultraviolet to infrared wavelengths. This allows graphene to carry more data than current state-of-the-art modulators, which operate at a bandwidth of up to 10 nanometers, the researchers said.

"Graphene-based modulators not only offer an increase in modulation speed, they can enable greater amounts of data packed into each pulse," said Zhang. "Instead of broadband, we will have 'extremeband.' What we see here and going forward with graphene-based modulators are tremendous improvements, not only in consumer electronics, but in any field that is now limited by data transmission speeds, including bioinformatics and weather forecasting. We hope to see industrial applications of this new device in the next few years."

Other UC Berkeley co-authors of this paper are graduate student Erick Ulin-Avila and post-doctoral researcher Thomas Zentgraf in Zhang's lab; and visiting scholar Baisong Geng and graduate student Long Ju in Wang's lab.

This work was supported through the Center for Scalable and Integrated Nano-Manufacturing (SINAM), an NSF Nanoscale Science and Engineering Center. Funding from the Department of Energy's Basic Energy Science program at Lawrence Berkeley National Laboratory also helped support this research.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of California - Berkeley. The original article was written by Sarah Yang, Media Relations.

Journal Reference:

Ming Liu, Xiaobo Yin, Erick Ulin-Avila, Baisong Geng, Thomas Zentgraf, Long Ju, Feng Wang, Xiang Zhang. A graphene-based broadband optical modulator. Nature, 2011; DOI: 10.1038/nature10067

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here