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Researchers hope to use networks of unused, dark fiber optic cables to help detect underground sound waves that can warn of an impending earthquake.
Millions of miles of unused, dark fiber optic cables are installed underground. A research team of scientists from the University of California (Berkeley) and Lawrence Berkeley National Lab have been experimenting with a new predictive technique. This method may gather measurements of movement in the Earth’s crust that are superior to those obtained by current seismic detection systems.
Measuring Activity
In seismology, scientists often have only a small number of sensors to use in detecting earthquakes. This is one reason why measuring vibrations through the Earth’s surface is an uneven, “touch-and-go” venture. Also, some seismically-active areas have many sensors on hand, while places distant from shifting tectonic plates may have very few. This variation in equipment can make it tough to measure seismic vibrations in places where, for example, fracking triggers earthquakes. Using the new method, users could turn each fiber optic cable length of a few feet into an individual seismic sensor.
In this new experiment, the research team “borrowed” from other groups who have developed distributed acoustic sensing (DAS) methods. In DAS, laser pulses are used to detect minute vibrations along optical fiber/cable. Researchers insert units called interrogators along the optical fiber/cable. These interrogator units send out and sense short infrared laser pulses. Triggered by seismic activity, tiny strains on the optical fibers cause some of the laser light to be reflected and then bounced back to the sensor. By sending rapid pulses, the scientists can detect changes in the light scattering over time. By knowing the speed of light, they can pinpoint where the activity occurred.
“Real World” Testing
With this latest technique, the researchers essentially tested the DAS method in the real world. They plugged their interrogators into the fiber optic cable line along the Department of Energy’s Dark Fiber Testbed. This 13,000-mile stretch of telecommunications fiber in the western U.S. is used for testing new communications equipment. The researchers targeted a 17-mile cable segment near West Sacramento, California, and recorded data from July 28, 2017, up to January 18, 2018.
The research team successfully recorded information on the speed of sound waves traveling through the Earth. In fact, during September 2017, they detected and measured the massive 8.1 magnitude earthquake in Mexico (the strongest quake to hit Mexico in a century).
Unfortunately, this detection technique isn’t ready to be used beyond research. But keep an eye open for possible use in the future!
In 2013, Edward Snowden, a U.S. National Security Agency contractor, leaked documents showing that intelligence agencies were spying on the data of private citizens. One disturbing fact was that the spies tapped into optical fiber cables to access the huge amount of data moving through these cables.
Snowden’s disclosures pushed researchers to use quantum science to make this type of hacking impossible. Finally, there are reports of progress.
THE QUANTUM KEY DISTRIBUTION APPROACH
A startup called Quantum Xchange will access 500 miles of optical cable along the Eastern U.S. coast. Quantum will use this cable to create the country’s first quantum key distribution (QKD) network.
Quantum Xchange’s “QKD approach” would send an encoded message in bits while transmitting the decoding keys as quantum bits, or qubits. Usually in the form of photons, the qubits travel easily along fiber cables. However, any attempt to spy on a qubit would instantly destroy its fragile quantum state, erase any data and leave the mark of an intrusion.
One possible issue is that “trusted nodes” must be used to send quantum keys over long distances. These nodes act as repeaters to boost signals in a typical data cable. Quantum Xchange plans to have 13 trusted nodes along its entire network. At these node points, keys are first turned into bits. Then, they are changed back to a quantum state to be sent on. In other words, a hacker could theoretically steal these bits as they are momentarily vulnerable.
AN ALTERNATE METHOD: QUANTUM TELEPORTATION
Along with this news, the University of Chicago, the Fermi National Accelerator Laboratory and Argonne National Laboratory will jointly develop a test bed to use quantum teleportation to create secure data transmission.
Quantum teleportation would use entanglement to eliminate the risk of hacking. Entanglement creates a pair of qubits (usually photons) in a single quantum state. A change in one photon instantly affects the linked photon, even if they are far apart. Therefore, in theory, it should be impossible to hack data transmission using entanglement. This is so because tampering with one of the qubits would destroy both quantum states.
However, the entanglement method is still confined to research labs. And there are huge challenges to making this approach work in the real world. According to Dr. David Awschalom of the University of Chicago, creating and maintaining entanglement would be extremely difficult over a long haul fiber optic network.
Dr. Awschalom is leading the project involving the university and the national labs. The goal is to have the test bed use a “plug-and-play” approach that will let the researchers experiment and evaluate different techniques for entangling and transmitting qubits.
The U.S. Department of Energy will provide several million dollars to fund the test bed. This test bed will use a 30-mile stretch of installed optical cable between the labs. Members of the Chicago Quantum Exchange will operate the test bed and project. This Exchange consists of 70 scientists and engineers from the three organizations.
Engineers at the California Institute of Technology have created the world’s smallest fiber optic gyroscopeto aid in navigational sensing. Five hundred times smaller than a regular gyroscope, this new gyro can fit on a grain of rice. This research breakthrough could lead to more accurate fiber optic gyros compared to mechanical units.
WHAT OPTICAL GYROS DO
Advanced fiber optic navigation technology is critical for aircraft, missiles, unmanned aerial vehicles and ground vehicles. These machines and other platforms depend on fiber optic gyroscopes to operate safely.
HOW THEY DO THEY WORK?
A fiber optic gyroscope detects changes in position or direction using the Sagnac effect. In this way, an optical gyro functions similarly to a mechanical gyro. However, the optical gyro operates by using light passing through a coil of optical fiber.
Inside a typical optical gyroscope, a spooled-up optical fiber carries pulses of laser light. Some pulses move clockwise and others go counterclockwise. The gyro measures rotation by detecting tiny changes in how these pulses arrive at a sensor. Researchers have tried to create smaller optical gyros. However, as the size of the gyro shrinks, the signals from its sensor have grown weaker until they are drowned out by “noise” from scattered light.
WHAT THE TEAM DID
The Cal Tech research team designed a low-noise, photonic gyroscope. They etched light-guiding channels onto a two-square-millimeter silicon chip. These channels guide the light in each direction around a separate circle. This layout keeps scattered light from confusing the device’s sensors. The new design also reverses the light’s direction from time to time. This change helps to cancel out much of the related “noise.”
Optical gyroscopes that use the Sagnac effect to measure rotation could eventually be miniaturized onto nano-photonic platforms. However, thermal fluctuations, component drift and fabrication mismatch often limit the signal-to-noise ratio of these gyros. Because a microscale unit would have a weaker signal, researchers have not yet created an integrated nano-photonic fiber optic gyroscope.
Interested in fiber optic sensing? If so, you’ll want to check out the “Tales From the Front Line of Fiber Optic Sensing” webinar presented by OptaSense and sponsored by the Fiber Optic Sensing Association (FOSA).
Whether it’s detecting pipeline leaks, damage to railroads or intrusion at critical facilities, fiber optic sensing plays an increasingly important role in protecting and keeping key infrastructure assets operating globally.
The webinar features fiber optic sensing installations across a wide range of industry verticals, applications and locations, including system action videos with the challenges and successes of actual deployments.
To download and view this webinar, go here.
To subscribe to the FOSA e-newsletter, go here.
To support the exponential growth of global data traffic, 100 Gb/s submarine transmission systems are being installed in transoceanic links. These systems offer capacity up to ~10 Tb/s on a single core fiber using a C-band Erbium doped fiber amplifier (EDFA).
However, there are distinct challenges involved in developing and deploying high-capacity transoceanic distance transmissions systems. One issue is the need to improve optical signal-to-noise ratio (OSNR) within the entire C- and L-bands. Another limitation lies in delivering electrical power to the offshore equipment supplying EDFA pumps. In addition, long haul undersea submarine systems are typically much longer than terrestrial systems and have unique requirements for fiber optic cables and repeaters used in harsh subsea environments.
In a new white paper presented at SubOptic 2016, OFS and OFS Labs researchers discuss key fiber and amplifier technologies that help users to achieve high capacity and long reach for submarine transmission systems. These technologies include ultra-large-effective area, low loss optical fibers and their impact on performance, along with key amplification techniques for both repeatered and repeaterless submarine systems.
Researchers hope to use networks of unused, dark fiber optic cables to help detect underground sound waves that can warn of an impending earthquake.
Engineers at the California Institute of Technology have created the world’s smallest 
