Researchers from VTT have developed a wood-based optical fiber. The fiber, made from cellulose, is suited for sensors that benefit from biodegradability. In the future, optical cellulose fiber may allow detecting changes in the moisture level of buildings. The core of the fiber is surrounded by a cellulose acetate cladding material with a lower index of refraction, which allows light to travel through the fiber. The materials used in cellulose fibers are able to react with the substances being measured and absorb them, something that is difficult for glass or plastic fibers. “We have tested the suitability of the fiber for measuring moisture levels,” said research scientist Ari Hokkanen of VTT. “Using a length of fiber of a few centimeters, we have already succeeded to increase the attenuation of light transmitted in the fiber many orders of magnitudes.” Cellulose effectively absorbs and releases water, which can be measured by the change in the attenuation of light transmitted in the fiber. Cellulose is also easy to modify in terms of the index of refraction. VTT developed an optical fiber made of cellulose. Optical fiber made of cellulose is best suited for sensors that benefit from the biodegradability of the material. Courtesy of VTT. Cellulose-based fiber opens up new opportunities for sensor applications, but will not compete with glass-based optical fibers in telecommunications applications. “The [research and development] is still in its initial phases so we do not yet know all the applications the new optical fiber could lend itself to,” said senior scientist Hannes Orelma of VTT. The development of the optical fiber began in VTT’s iBex program. The research continues in the FinnCERES flagship program in collaboration with VTT and Aalto University. The research was published in Cellulose Journal (www.doi.org/10.1007/s10570-019-02882-3).