Finnish researchers have made an optical fiber made entirely of cellulose, much cheaper and more environmentally friendly than conventional glass and plastic fiber. If its optical performance remains limited over long distances, it offers additional advantages for many other applications.
The optical submarine cables now cover more than 1.2 million kilometers between continents, according to the website TeleGeography. And that’s without counting the optical fiber that connects each of our homes to provide us with an ultra-fast connection to Internet or television services. Fiber optics also finds many outlets in the medical field ( endoscopes, phototherapy, dental), in lighting, transport or the military.
These millions of cables are generally made up of a “core” of glass and plastic , and which have excellent optical properties, then they are covered with a sheath with a lower refractive index in order to guide the light to the inside. Unfortunately, these materials are often expensive and non-renewable.
The wood that drives light
Researchers at the National Center of Technical Research of Finland – VTT (acronym for Valtion Teknillinen Tutkimuskeskus ) turned to a material more environmentally friendly, biodegradable and cheap: the wood . They have developed an optical fiber made of 100% cellulose . Wood is however not particularly known as a good light conductor. In recent years, however, we have managed to make the wood transparent, eliminating its lignin and mixing it with a transparent polymer.
Finnish researchers have focused on cellulose extracted from wood. They first dissolved it in a solvent, then immersed it in water, which made the cellulose coagulate. They recovered a perfectly transparent optical fiber, with a high refractive index, which was then dried, then covered with cellulose acetate, at the lowest refractive index.
This eco-friendly fiber, which has good thermal and mechanical resistance, transmits light in a spectrum ranging from 500 to 1,400 nm, which corresponds to the wavelengths used for telecommunications. However, it is far from achieving the performance of the conventional optical fiber. Its attenuation factor, which measures the loss of the signal during transmission, is around 6.3 dB/cm, where the best fibers with a silica core reach 0.1 dB/km.