As a result of a scientific accident whilst researching the nonlinear effect of intense laser light in optical fibers, a scientist call Kenneth Hill at the Communication Research Center accidently created an in-fiber reflection grating from localized photo-induced refractive index changes. This led to the development of photosensitive fibers and the birth of the fiber Bragg industry. Hill's discovery rapidly paved the way for the development of wavelength-selective reflectors based on Bragg's law, which became the fundamental principle behind the design of fiber Bragg gratings - the primary application of photosensitive fibers.
The demand for FBGs increased rapidly during the growth of the telecommunications industry, and new applications that arose during this time were a strong driver for research and development into FBGs. However the manufacturing capacity of these early devices limited the growth of the industry, and this led to the development of more powerful lasers, higher quality phase masks and optical fibers with greater photosensitivity so that fast FBG inscription speeds could be achieved.
As well as high photosensitivity, fibers used in these applications need to withstand the bend losses which occur when tight bends are formed with the fiber during their deployment, losses resulting from the mode field no longer guiding tightly within the center of the core. Fibercore's highly photosensitive range of specialty singlemode fibers meet both these requirements - increased Germania for enhanced photosensitivity and high NA for low bend-loss - the SM1500(4.2/xxx) fibers are especially suitable for these applications. Fibercore's PS range of intrinisically photosensitive fiber offers a high Germania content with a lower NA and does not require hydrogen loading to encourage absorption into the core.
To find out more, visit Nature Photonics (Nature Photonics/Vol 5/August 2011) and read Dr Andy Gillooly's article on 'Growing Gratings'. Andy is the Senior Sales Engineer at Fibercore Ltd and has a PhD in Fiber Bragg Gratings as well as an industrial background in FBGs and lasers.