Fiber Bragg Gratings

A Fiber Bragg Grating (FBG) can, in its simplest context be seen as complex signal processing within the core of an optical fiber or as an optical filter where a part of the incident light is either being transmitted or reflected. Since the grating is written in the actual core of the fiber it interacts with the light being transmitted.

A grating is generated by exposing the core, typically no more than 5 μm in diameter (i.e. a tenth of the diameter of a normal human body‐hair), of a specially prepared optical fiber to a fringe pattern of ultraviolet light. The ultraviolet light will locally induce changes in the refractive index of the core. A change in refractive index will be seen as a tiny mirror by the light trying to pass through the grating, and a small portion will be reflected.

By generating many of these local mirrors in sequence at well defined distances, an optically resonant cavity is produced. By tuning the distance and amplitude between the mirror elements, the filter characteristics (e.g. the wavelengths and amount of reflected light) can also be tuned. The result is a so called chirped FBG.

Proximion’s versatile and proprietary grating writing technology utilizes a two‐beam interferometer to create the fringe pattern of ultraviolet light used for inducing the change of refractive index. A highly accurate motion controller can sequentially add up these fringe patterns with sub nanometer precision over long distances.