Science

Liquid-filled optical fiber designed for more robust data transmission

Liquid-filled optical fiber de...
The glycerol-filled fiber withstands bending, and can be stretched by up to 10 percent without breaking
The glycerol-filled fiber withstands bending, and can be stretched by up to 10 percent without breaking
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The glycerol-filled fiber withstands bending, and can be stretched by up to 10 percent without breaking
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The glycerol-filled fiber withstands bending, and can be stretched by up to 10 percent without breaking
The fiber may have other applications besides data transmission
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The fiber may have other applications besides data transmission

Although optical fibers are highly effective at data transmission, they're also relatively brittle. An experimental new type of optical fiber addresses that limitation, by incorporating a core made of liquid glycerol.

Ordinarily, optical fibers are made of either solid glass or a solid transparent plastic. The former is able to carry light pulses over a longer distance, but will break fairly easily if bent or stretched. The latter – which is useful over shorter distances, such as within buildings – stands up better to bending, but stretching it will still cause it to break.

Seeking an alternative, researchers at Switzerland's Empa institute have developed an optical fiber consisting of a continuous liquid glycerol core contained within a transparent fluoropolymer sheath.

"The two components of the fiber must pass through our spinneret together under high pressure and at 200 to 300 degrees Celsius [392 to 572 ºF]," says the lead scientist, Dr. Rudolf Hufenus. "So we need a liquid with a suitable refractive index for functionality and with the lowest possible vapor pressure to produce the fiber."

The resulting fiber's ability to transmit data in the form of light pulses is approximately equal to that of solid plastic optical fibers, but it has much higher tensile strength – in other words, it's significantly better at withstanding stretching.

The fiber may have other applications besides data transmission
The fiber may have other applications besides data transmission

As an added bonus, if the fiber is being stretched, its color will change. This is due to the fact that the same amount of glycerol will still be present within the fiber, but because the liquid is being spread out over a longer distance, red dye particles within it will be farther apart from one another. As a result, the color of the light that's emitted through the sheath will subtly change. That color-change could be measured using an optical sensor, letting users know that the fiber – and thus a device incorporating it – is lengthening or being subjected to a tensile load.

All of that being said, won't the glycerol just leak out when the fiber is cut to the desired length? "Under normal conditions, the liquid core is kept inside the fiber due to capillary forces; however, when a pressure is applied on the fiber, the liquid can be pressed out of the fiber tip," Hufenus tells us. "This can be prevented by sealing the fiber end with a hot blade."

Ultimately, it is hoped that the fiber will find use not only in less fragile data transmission, but also for force transmission in micromotors or microhydraulic systems.

Source: Empa

2 comments
2 comments
Kpar
As a retired fiber optic splicer, I am curious as to how these liquid filled fibers are spliced together. We always used fusion splicers- wouldn't the heat cause a vaporization problem? Bubbles were an occasional problem, even with solid glass fibers.
Bob Flint
From a mechanical standpoint, it's technically a tube, yes the thinner walls maybe more fragile but that's where the liquid fill comes in to prevent tubular collapse during bending and manipulation. Sort of like using sand when bending metal pipes. The liquid inside is the actual transport medium, therefore when pulled the side walls shrink inwards, and the fluid cross section is reduced in volume equal to the force of pulling, but still allows transmission?