Nav: Home

Fiber sensors may leave the jacket on

January 28, 2019

Optical fibers enable the internet, and they are practically everywhere: underground and beneath the oceans. Fibers can do more than just carry information: they are also fantastic sensors. Hair-thin optical fibers support measurements over hundreds of km, may be embedded in almost any structure, operate in hazardous environments and withstand electro-magnetic interference.

Recently a major breakthrough in optical fiber sensors facilitated the mapping of liquids outside the boundary of the glass fiber, even though guided light in the fiber never reaches there directly. Such seemingly paradoxical measurements are based on the physical principle of opto-mechanics. The propagation of light, in and of itself, is sufficient to induce ultrasonic waves in the optical fiber. These ultrasound waves, in turn, can probe the surroundings of the fiber, similar to ultrasonic imaging that is common in medical diagnostics. The analysis of liquids outside km of fiber was reported independently by researchers from Bar-Ilan University, Israel and EPFL, Switzerland.

The results obtained to date all suffered, however, from one major drawback: the protective polymer coating of the thin glass fiber had to be removed first. Without such protective coating, or "jacket" as it is often referred to, bare fibers of 125 micro-meters diameter do not stand much chance. One cannot consider the application of kilometers-long, unprotected optical fibers outside the research laboratory. Unfortunately, the standard coating of fibers is made with an inner layer of acrylic polymer that is extremely compliant. The layer completely absorbs ultrasonic waves coming out of the optical fiber, and keeps them from reaching any media under test. The presence of coating represents one more barrier that the sensor concept must overcome.

The solution to this challenge comes in the form of a different, suitable coating. Commercially-available fibers can also be protected by a jacket made of polyimide. The specific material was originally proposed for protecting the fiber at high temperatures. However, recent studies at Bar-Ilan and EPFL have demonstrated that the polyimide coating also provides transmission of ultrasound. The consequences are significant: researchers at Bar-Ilan University report in a new article published in the journal Applied Physics Letters- Photonics that they are now able to perform opto-mechanical sensing and analysis of media that lie outside protected fibers, which can be deployed in proper scenarios.

"Polyimide coating lets us enjoy the best of both worlds," says Prof. Avi Zadok from the Faculty of Engineering, Bar-Ilan University. "It gives the fiber a degree of protection, alongside mechanical connectivity with the outside world." Zadok and research students Hilel Hagai Diamandi, Yosef London and Gil Bashan performed a thorough analysis of light-sound interactions in coated fibers. The joint structure supports a host of elastic modes, which exhibit complex coupling dynamics. "Our analysis shows that the opto-mechanical behavior is much more complex than that of a bare fiber," says Zadok. "The results strongly depend on sub-micron tolerances in the thickness and geometry of the coating layer. A proper form of calibration is mandatory."

Despite this added difficulty, the mapping of liquids outside coated fibers has been demonstrated experimentally. The group achieved sensing over 1.6 km of polyimide-coated fiber, which was immersed in water for most of its length. A 200 meter-long section, however, was kept in ethanol instead. The measurements distinguish between the two liquids, and properly locate the section placed in ethanol. The results represent a major milestone for this up and coming sensor concept. "One possible application," says Prof. Zadok, "is the monitoring of irrigation. The presence of water modifies the properties of the coating. Our measurements protocol is able to identify such changes." Ongoing work is dedicated to improving the range, resolution and precision of the measurements.
The research was funded by grants from the European Research Council (ERC), the Israel Ministry of Science and Technology, and an Azrieli Fellowship.

Bar-Ilan University

Related Optical Fiber Articles:

For gut microbes, not all types of fiber are created equal
Certain human gut microbes with links to health thrive when fed specific types of ingredients in dietary fibers, according to a new study from Washington University School of Medicine in St.
Entanglement sent over 50 km of optical fiber
For the first time, a team led by Innsbruck physicist Ben Lanyon has sent a light particle entangled with matter over 50 km of optical fiber.
Fiber-based artificial muscles get new and powerful twists
Three papers in this issue demonstrate new fiber-based designs within the world of artificial muscles, showing how these twisted and coiled designs can be controlled via heat, electricity and chemistry.
Fiber-optic probe can see molecular bonds
Engineers at UC Riverside have developed the world's first portable, inexpensive, optical nanoscopy tool that integrates a glass optical fiber with a silver nanowire condenser.
Why you should care about better fiber optics
With a new method, the gallium antimonide is initially distributed throughout the silicon.
More Optical Fiber News and Optical Fiber Current Events

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Rethinking Anger
Anger is universal and complex: it can be quiet, festering, justified, vengeful, and destructive. This hour, TED speakers explore the many sides of anger, why we need it, and who's allowed to feel it. Guests include psychologists Ryan Martin and Russell Kolts, writer Soraya Chemaly, former talk radio host Lisa Fritsch, and business professor Dan Moshavi.
Now Playing: Science for the People

#537 Science Journalism, Hold the Hype
Everyone's seen a piece of science getting over-exaggerated in the media. Most people would be quick to blame journalists and big media for getting in wrong. In many cases, you'd be right. But there's other sources of hype in science journalism. and one of them can be found in the humble, and little-known press release. We're talking with Chris Chambers about doing science about science journalism, and where the hype creeps in. Related links: The association between exaggeration in health related science news and academic press releases: retrospective observational study Claims of causality in health news: a randomised trial This...