Distributed Acoustic Sensing (DAS) is a technology that enables continuous, real-time measurements along the entire length of a fiber optic cable. Unlike traditional sensors that rely on discrete sensors measuring at pre-determined points, distributed sensing utilizes the optical fibre. The optical fiber is the sensing element. These systems allow acoustic signals to be detected over large distances and in harsh environments.
AcoustiSens® Wideband Single-Mode Optical Fiber, the newest addition to the OFS LineaSens® family, is a vibration sensing fiber with optimal performance for DAS systems. Using a waveguide design based on the ITU-T G.657.A1 telecom-grade single-mode standard, AcoustiSens Wideband Optical Fibers significantly increase Rayleigh backscatter while maintaining low attenuation to improve Optical Signal to Noise Ratio (OSNR). Furthermore, the AcoustiSens Wideband Optical Fibers provide bend-insensitivity and expand the operating wavelength band (1536 – 1556 nm) ensuring interoperability with all known DAS interrogators.
AcoustiSens Wideband is intended for use in cables designed as sensing components in Distributed Acoustic Sensing (DAS) systems. Without the need for changes in interrogation equipment or complex optical amplification schemes AcoustiSens Wideband is a drop-in fiber replacement that provides greatly improved sensing performance with OSNR orders of magnitude better than telecom-standard fibers. This translates into significantly improved ASNR in DAS systems. Due to its waveguide design, AcoustiSens fibers are also bend-insensitive and splice compatible with G.657.A1 and G.652.D optical fibers, assuring smooth integration with commonly deployed sensing solutions.
AcoustiSens Optical Fibers are intended for use as components in optical and hybrid cables designed for vibration or acoustic sensing applications including:
- Pipeline monitoring (midstream)
- Rail monitoring
- Perimeter monitoring
- Subsea monitoring
- Highway monitoring
- Smart City applications
To learn more about AcoustiSens watch this video overview or visit the OFS website. Or you may contact us to discuss solutions to your sensing needs.
Seismologists from the California Institute of Technology (Caltech) are using fiber optic network cable to monitor and record aftershocks from the July 4 and 5 Ridgecrest, CA, earthquakes. By using optical fiber, the scientists can gather, track, and analyze data in much greater depth from the thousands of daily aftershocks.
To do this, the scientists send a beam of light down optical fiber in an unused or “dark” fiber optic cable. When the light reaches tiny blemishes in the optical fiber, a small portion of the light is reflected back and recorded. In this way, each fiber imperfection acts as a trackable location along the buried fiber optic cable. When seismic waves move through the ground, the cable expands and contracts slightly. This change affects the travel time of light to and from the locations. By monitoring these changes, seismologists can monitor the motion of seismic waves.
According to Caltech, the miniscule fiber imperfections occur often enough so that every few meters of optical fiber act as an individual seismometer. In fact, monitoring 50 kilometers of fiber optic cable in three different locations is roughly equal to deploying more than 6,000 seismometers in the area.
Caltech launched the project within days of the two large earthquakes and began contacting groups in a search for unused fiber optic cable that would be close enough and long enough to be useful. The scientists finally contacted the California Broadband Cooperative’s Digital 395 project. The goal of the Digital 395 project is to build a new 583-mile fiber optic network that will run north to south, along the eastern Sierra Nevada, passing near Ridgecrest. Digital 395 offered three segments of its fiber cable to which Caltech connected sensing instruments.
Information gathered from the Ridgecrest fiber network will help seismologists learn more about the way that earthquakes move through the earth, and specifically how seismic waves move through the area around Ridgecrest.
Many land and oceanic oil operations use temperature sensing to help improve safety and functionality in harsh environments. Optical fibers used in these conditions are routinely exposed to high temperatures and pressures, along with ionizing radiation and aggressive chemicals in the surroundings.
Given these extremes, companies are increasingly using silica-based optical fibers for both acoustic and distributed temperature sensing. These fibers offer advanced properties including superior thermal stability and mechanical robustness. They are also able to transmit optical power with minimal added attenuation or signal loss.
While researchers have thoroughly studied the mechanical strength of optical fibers under ambient conditions, they have rarely examined fibers after exposure to elevated temperatures and/or liquids. In fact, to the best of our knowledge, there is no systematic data documenting the mechanical strength of optical fibers placed under high temperatures and pressures such as those experienced in temperature sensing.
That’s why when Andrei Stolov of OFS decided to perform an experimental study, he was operating in somewhat “unknown territory.” Before beginning the experiment, Stolov realized that a number of factors would influence whether optical fibers could survive the harsh conditions found in oil operations. These aspects include the type of fiber coating, environment, temperature, pressure and usage time.
When optical fibers are used at elevated temperatures or in aggressive environments, the most frequent indications of failure are added attenuation or loss of mechanical strength. In Stolov’s study, he used strength degradation as his criteria for failure.
In his experiment, Stolov submerged a range of optical fibers with various coatings into four high-temperature/high-pressure fluids, namely (1) distilled water; (2) sea water; (3) isopropyl alcohol (IPA); and (4) paraffin oil. Undersea and downhole applications primarily drove his choice of fluids. In these situations, fibers can be exposed to these or similar environments.
To learn more about the study and the results, please go HERE.
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.
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!
A new, air-filled optical fiber bundle could dramatically improve medical endoscopes. This technology could also help create endoscopes that produce images using infrared wavelengths. If so, this breakthrough would allow diagnostic procedures that aren’t currently possible.
In the Optical Society (OSA) journal Optics Letters, University of Bath (U.K.) researchers showed that these new fiber optic bundles (called air-clad imaging fibers) deliver resolution equal to the best commercial imaging fibers. And the bundles do this at twice the wavelength range of these fibers. Because of this, these air-clad imaging fibers could help create new, smaller endoscopes with even better resolutions.
HOW ENDOSCOPES WORK
Used in minor surgery and imaging, endoscopes use bundles of optical fibers to obtain images from inside the body. Light that falls on one end of the fiber bundle travels through each fiber to the far end. This process sends a picture as thousands of spots, much like pixels in a digital picture.
TESTING THE BUNDLES
Instead of using cores and claddings of two types of glass, the new bundles use an array of glass cores covered by hollow glass capillaries filled with air. These air-filled capillaries act as the fiber cladding.
To test the imaging fibers, the research team created an air-clad fiber bundle. This bundle matched the resolution of a leading commercial fiber (with the same spacing between cores). The team then stacked multiple, smaller honeycomb structures to place more than 11,000 cores into the fiber.
The researchers used the air-clad fiber bundle and the commercial fiber to image a standard test target image. And the result? The air-clad fiber performed well beyond the wavelength range that a visible camera could detect. And when the researchers switched to an infrared camera, the fiber created a clear image at twice the wavelength that the commercial fiber reached.
REAL-WORLD USE OF FIBER BUNDLES
Along with medical diagnosis and care, the new optical fiber bundles could be used for industrial applications. These uses include monitoring the contents of hazardous machines and viewing the inside of oil and mineral drills. These types of fibers are becoming more and more popular for a variety of purposes.
OFS Laboratories, one of the world’s leading optical fiber research labs, and the research arm of OFS, has performed major work in this area. The development of Microstructure Optical Fibers (MOFs) is one result of this work. The MOFs created by OFS Labs are a new class of optical fibers that are substantially different from conventional optical fibers.
> Learn More our Optical Medical Solutions
Companies use optical fiber as a sensor to detect changes in temperature and pressure. This technique is often used to monitor structures including bridges and gas pipelines.
Now researchers at Ecole Polytechnique Fédérale De Lausanne (EPFL) have discovered a new method where optical fibers can identify when they are in contact with a liquid or a solid. The researchers accomplished this by generating a sound wave with help from a light beam inside the optical fiber.
A Sensor That Doesn’t Disrupt the Light
Four factors affect the light carried by a glass optical fiber: intensity, phase, polarization and wavelength. These factors can change when something stretches the fiber or the temperature varies. These changes let the fiber act as a sensor by detecting cracks in structures or temperature changes. However, until now, users could not know what was actually happening around the fiber without letting light escape, which interrupts the light path.
The method from EPFL uses a sound wave generated inside the fiber. This hyper-frequency wave regularly bounces off of the fiber’s walls. This echo varies at different locations depending on the type of material that the wave contacts. The echoes leave an imprint on the light that users can read when the beam exits the fiber. While users can study this imprint to detect and map out the fiber’s surroundings, it is so faint that it barely disturbs the light within the fiber. In fact, users could employ this technique to sense what is occurring around a fiber and send light-based information at the same time.
In experiments, the researchers submerged their fibers in water and then in alcohol, and left them out in the open air. Each time, their system correctly identified the change in the fibers’ surroundings. The group expects their technique to have many potential applications by detecting water leakage, as well as the density and salinity of fluids that touch the fiber.
Spatial and Temporal Detection
This method discerns changes in the surroundings with a time-based method. Each wave impulse is created with a slight time jag. Then, when the beam arrives, the delay is reflected. The researchers can see what any disturbances were and determine their location. The group can currently locate disturbances to within 10 meters, but have the technical means and expect to increase accuracy down to one meter.
To read and learn more, go HERE.
With the growing need to accurately monitor processes in harsh environments, optical fibers are becoming an essential element within monitoring systems, both as the communications line and as the sensing element. Optical fiber sensors have been widely adopted and used in pipeline monitoring, perimeter monitoring, heat detection and structural monitoring systems, all of which operate within the typical 45 °C to 85 °C temperature range of a standard optical fiber.
However, as industries push their sensing requirements into environments such as those found in oil wells (for downhole measurement) and nuclear reactors, there is a need for optical fibers that can tolerate these extremely high temperatures and challenging environments.
Specifically developed for harsh temperature sensing and communications environments, the new PYROCOAT K Optical Fiber is up to the challenge. This mechanically-strong fiber features an improved coating that provides excellent thermal stability, enabling wider operating temperatures than other commercially available polymer-coated fibers. In fact, the PYROCOAT K Optical Fiber provides reliable performance even when subjected to extreme, long-term, high temperature exposure. (more…)
An international research group has developed a world-first fiber optic technology which may help detect a wide range of gases with unprecedented sensitivity. Published in the journal Optica, the discovery involves the creation of a fiber optic device which consists of an invisible infrared laser coupled to an ultra-broadband supercontinuum generator – two elements that researchers have never managed to combine into a single optical system before. Led by Macquarie University scientists in Australia, the group believes that potential applications for this technology range from breath analysis to air-quality monitoring.
According to lead researcher Dr. Darren Hudson of Macquaraie University, “This new supercontinuum technology is capable of being used to detect an array of gases, including methane, carbon dioxide and nitrous oxide – gases that can be harmful to humans in high levels and have implications in climate change.”
Over the past decade, researchers around the globe have worked to create high-brightness sources of infrared light – an invisible form of light that sits just beyond visible red light in the spectrum. While this work has revolutionized how we detect and measure a staggering range of molecules, the current technology still requires large laser systems, optical laboratory conditions and an expert operator. (more…)
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.
If so, don’t fret. This session on “Optical Fibers for Automation Controls and Industrial Networking” is still available for viewing.
Specifically designed for integrators, this webinar discusses the challenge of transforming Industrial Automation configurations, using Industrial Ethernet, to achieve a factory floor that features a more intelligent, efficient and sophisticated network.
This session will also enhance your ability to support customers in making the most environmentally appropriate fiber optic investments.
To access and view this webinar, go HERE.