Fantastic fibre-optics—sponge’s super spicules
Optical fibres are very fine fibres of glass about 120 microns in diameter (an average human hair is 50–70 microns thick). They comprise a core plus a cladding made from a different type of glass, so if light is shone into one end of the fibre, the cladding reflects light back into the fibre and prevents it from escaping (called total internal reflection). Therefore they act as wave guides which can transmit light along the length of the fibre.1
They have revolutionized the telecommunications industry, because they can conduct signals of voice or computer data in the form of light pulses for 50 km (30 miles) without a repeater to boost signals. While copper wires conduct the same information, but in the form of electrical impulses, optical fibres have many advantages. They are much lighter, require less power, can carry far more channels of information, are immune to electromagnetic interference and are harder to hack into without detection.1
The deep-sea sponge Euplectella, or the Venus flower basket, grows attractive glassy fibres, called spicules. Now, researchers led by Joanna Aizenberg of Bell Laboratories in New Jersey have shown that these are superb optical fibres.2
The sponge’s fibres are 5–15 cm (2–6 inches) long, and 40–70 microns in diameter, about the thickness of human hair, so are finer than man-made fibres. They have an elaborate structure: a core of pure silica glass 2 microns in diameter surrounding an ultra-thin organic filament, and a finely layered shell.
The shell works as optical cladding just like in man-made fibres, making them excellent wave guides. They conduct light very well because they have small amounts of sodium ions. The sponge can add these ions in a controlled way using organic molecules at ordinary temperatures. But artificial optic fibres are made at temperatures high enough to partially melt glass; adding controlled amounts of sodium ions is a real challenge because it makes the fibres lose their glassiness.2
The sponge’s fibres are far more flexible than man-made ones—you can even tie a knot with them without them breaking. Man-made fibres break, because once a small crack starts, it spreads easily through a brittle material like glass. This is a major cause of outages in commercial optical fibres, and requires costly repairs.3 But the boundaries between the fine layers of the shell of the sponge fibres stop the crack from spreading.2
Geri Richmond of the University of Oregon said, ‘It’s such a wonderful example of how exquisite nature is as a designer and builder of complex systems.’4 Dr Aizenberg herself said, ‘We’re in the stone age compared to nature.’4 But crediting nature instead of nature’s Creator is the folly of Romans 1:25.
- Fibre Optic Technology: Introduction, Bell College of Technology, UK, <floti.bell.ac.uk/MathsPhysics/introduction.htm>, 19 November 2003.
- Sundar, V.C., Yablon, A.D., Grazul, J.L., Ilan, M. and Aizenberg, J., Fibre-optical properties of a glass sponge, Nature 424(6951):899–900, 21 August 2003.
- Grad, P., Inspirational sponge, Engineers Australia 75(11):30, November 2003.
- Cited in: McCall, W., Sponge has natural glass fiber optics, San Francisco Chronicle, p. A2, 8 August 2003.