Modern societies are facing rising concerns about global environmental issues, including an alarming rise in pollution of our seas, waterways, land, and air. As we bear witness to widespread industrialization along with mass consumption trends, environmental pollution has become more than a health issue; it poses a threat to entire ecosystems. Addressing these issues first requires us to know the nature of the beast. What is the scale of the problem? Fiber optic sensors could be the ideal tool in the armory needed to provide the real story of what is floating in our seas, leaking across our land, and wafting in the air around us. Fiber optics could help monitor and mitigate some of the serious environmental damage brought on by worldwide industrialization. Courtesy of Pixabay/Stevepb. Today, environmental monitoring services are extensively used in developed regions such as North America and Europe thanks to various stringent environmental monitoring regulations. Unfortunately, the introduction of these guidelines has led some companies to shift manufacturing operations to emerging countries where compliance has been weakly enforced. According to global market research and consulting service provider Global Market Insights Inc., in the last five years, government authorities in many emerging nations have in response further strengthened implementation of their environmental monitoring guidelines, driving a healthy demand for environmental monitoring devices in the Asia-Pacific and Latin America regions. With environmental monitoring on the up, the market for fiber optic sensors is projected to exceed $1 billion in 2022, according to the Photonic Sensor Consortium, with significant growth projected beyond 2022. “Environmental monitoring is important to protect food supply, water quality, structures from corrosion, and to detect potentially airborne contaminants,” said David Krohn, managing partner at Light Wave Venture LLC, based in Hamden, Conn. “Environmental monitoring will greatly expand in the areas of water safety, agriculture, transportation, smart structure protection, and biomedical monitoring.” Prevention better than cure New, stringent government regulations are encouraging organizations to focus on key issues such as sustainability. But apart from the moral obligation to look after the planet, investing in sensing and monitoring devices makes financial sense for many companies; sensors can save organizations substantial money by protecting infrastructure from catastrophic damage and locating specific issues to accelerate repair. Fiber optic sensors in particular offer an efficient way to monitor lengthy structures such as pipelines, which can extend over several hundreds of kilo-meters. “Fiber sensing applications serve to protect the structural integrity of the pipeline, helping to detect issues before a problem occurs,” said Stephanie Burris, product line manager of fiber monitoring products at San Jose, Calif.-based VIAVI Solutions Inc. “Moreover, by locating a leak, illegal tap, or an explosion in real time, this technology helps to minimize environmental damage as well as potential loss of life, products, and plants. The alternative methods of manual inspection or camera monitoring of vast distances of pipeline are expensive and not feasible for remote locations.” Sensor makers seek recognition Despite fiber optics being used for telecommunications for decades and in the sensing worlds for more than 20 years already, many in certain industries still see it as a new technology without a track record. For Etienne Rochat, chief technology officer at Omnisens SA in Morges, Switzerland, acceptance by end users and recognition of its potential to add value may be the biggest challenge for fiber optic sensors in this field. With fiber optics-based systems susceptible to physical damage during installation, a cost-effective solution could lie below our feet in the thousands of kilometers of fibers already available underground for data transmission. Courtesy of Pixabay/PDPics. “Fiber sensing is well adapted to long structures that could not be fully covered or measured using other methods like point sensors — either electrical or optical,” he said. “It can provide temperature, elongation/deformation, and vibration (with different sensing technology and sometimes dedicated cables) over multiple hundreds of kilometers (combining multiple instruments).” ‘Fiber sensing is a disruptive, new technology and there are very few similar alternatives that are cost-effective, technically feasible, and easy to apply.’ — Stephanie Burris, product line manager of fiber monitoring products at VIAVI Solutions Inc. Burris agreed. A continuous fiber allows for many more data points and offers a much more robust alternative to discrete sensors, which are expensive and lose all data when damaged. “Fiber sensing is a disruptive, new technology and there are very few similar alternatives that are cost-effective, technically feasible, and easy to apply,” she said. “Traditional electrical systems, like the thermostat in your home, have been used to sense temperature, but they are not practical over long distances where there is no power.” By applying a passive optical network fiber sensor solution in which no power is needed, monitoring can be maintained even when a natural disaster might take out the power. “All that is needed is a small, battery-powered optical-time domain reflectometer (OTDR) interrogator to take a trace of the fiber acting as the sensor,” Burris said. Without the constraints of an electricity supply, fiber sensors can monitor remote areas and withstand harsh environments that electronics cannot survive and where free-space spectroscopy is not possible. The sensing unit can be connected to the sensing head via a ruggedized optical fiber and separated over great distances; this is not the case for free-space spectroscopy, which requires an unobstructed line of sight. Distributed temperature sensing Fiber optic distributed temperature sensing (DTS) currently enjoys the lion’s share of fiber optic sensing for environmental applications. With origins in the oil and gas industry dating back to the late 1990s, DTS has become more powerful, and, in addition to temperature and strain, it can today monitor vibrations or acoustic response. Thanks to various technological advancements, a single fiber can discriminate between an animal and a human walking within its proximity, and distinguish the vibrations made by a car from those made by an aircraft. Some of the latest advancements are being carried out at leading research organizations, such as the U.K.’s Engineering and Physical Sciences Research Council (EPSRC)-funded Future Photonics Hub at the University of Southampton. Postdoctoral research fellow Ali Masoudi and professor Gilberto Brambilla highlight some of these improvements. “While optical fibers are usually encased in plastic jackets that insulate the light from the surrounding environment, in recent years special fibers with new coatings have become available that transfer the vibrations and strain across the coating and allow us to measure these natural events more effectively,” Masoudi said. “The availability of cheap gratings, cheap fibers, cheap sources, and cheap detectors means that optical fiber sensors have been deployed in open-air mines to determine slippage, and on volcanoes and hills to determine ground movements, mudslides, and subsidence.” As technology improves and costs come down, new and unexplored fields open up. Fiberized sensors can now explore the oceans, even at their deepest depths of 11 km, to understand what is going on at discrete depths from a single point at the surface. “A fiber under the ice pack (Arctic) would monitor 100 km from a single location,” Masoudi said, “which is extremely difficult or impossible to do from aerial surveys or satellites.” In open spaces, there is strong competition from free-space spectroscopy and remote sensors such as satellites or cameras mounted on planes or drones. It is below ground and underwater that distributed sensing really comes into its own. Large distances can be monitored and sensing can be performed remotely from a location up to 100 km from the sensing position. Fiberized sensors could be deployed for underwater monitoring within the proximity of offshore wind farms or for underground perimeter monitoring of natural reserves. “For this to happen, higher sensitivities to the event to detect (acoustic, pressure, or temperature) are desirable, and indeed a higher resolution,” Brambilla said. “Cheaper [and] faster electronics and broader internet will definitely help on this side.” Overcoming challenges An influx of technological advancements in spectrometry and chromatography makes stiff competition for purely fiber optics-based environmental monitoring devices. High installation costs coupled with the need for specialized test equipment prevents the devices from being used in some industries. What’s more, fiber optics-based systems are highly susceptible to physical damages during installation and construction activities. According to Global Market Insights Inc., such limitations restrict adoption in sectors with high-level infrastructural changes as well as by smaller companies that find it cost prohibitive. But optics makers are working hard to find solutions to these issues. More and more companies are developing fiber optics-based integrated solutions that incorporate competing technologies. For example, Vernier Software & Technology, a software and equipment company based in Beaverton, Ore., introduced a spectrophotometer optical fiber, specifically designed for emission spectrum testing. Fiberized sensors can now explore the oceans, which are as deep as 11 km, to understand what is going on at discrete depths from a single point at the surface. Courtesy of Pixabay/Vladvictoria. Changchun New Industries Optoelectronics Technology Co. Ltd. in Changchun, China, launched a fiber optic spectrometer with the added benefits of modulization and flexibility. Light Wave Venture’s Krohn believes that the future will likely see a combination of fiber optic sensors with wireless systems but that two major challenges remain: high cost and a broader range of applications. One cost-effective answer could be below our feet already. With much of the cost of utilizing fiber optic sensors stemming from its installation, why not take advantage of the thousands of kilometers of fibers already available in the ground or underwater for data transmission? Brambilla believes this to be a viable option, and when combined with another existing technology, further applications could be enabled. A distributed optical fiber acoustic sensing unit capable of measuring vibrations every 0.5 m along multiple kilometers of standard single-mode fiber. The strain sensitivity of this unit was measured to be 10 nε with maximum detectible strain of 1 mε. Courtesy of Ali Masoudi/ University of Southampton, U.K. “Data analysis can be cumbersome, as distributed sensors generate enormous amounts of data,” he said. “AI could be used to analyze data and recognize events that have not previously been identified, such as tsunami fingerprints or earthquake premonition events.” Future of fiber optic sensors While distributed fiber optic sensing has gathered momentum, exciting advancements in other branches of fiber optics, including fiber Bragg gratings, optical frequency domain reflectometry, and distributed acoustic sensing, have thus far been underutilized in environmental studies and are awaiting exploitation. These additional techniques could open up novel applications in hydrology, hydrogeology, geophysics, and other environmental fields in which high-accuracy, high-frequency, and/or high spatial resolution measurements are needed. For these applications, fiber optics sensing has mostly been used in the lab over short distances. But Burris points out that this may be about to change. “Work is ongoing to make it more affordable and practical to bring this to applications in the field to cover vast distances, inclement conditions, and to make it easier for the user through automation to enable simple pass/fail tests or alarms,” she said. VIAVI Solutions has managed to bring down cost and increase application by making improvements in form factor coupled with traditional Rayleigh optical-time domain reflectometry. “We also have a patented process to decorrelate the temperature and strain measurements taken at the same time on one fiber,” Burris added. “This means that the cost of measurement can be reduced as compared to requiring two fibers and then correlation of timing of events.” The technological advancements in the fiber optics landscape are providing numerous added advantages, such as portability and tolerance to extreme temperatures and corrosive conditions. These developments are expected to increase the usage of fiber optics. However, sensor makers will have to continue to encourage those who are unfamiliar with the technology to give fiber optics its due credit.