OVERVIEW OF FBG manufacturing technologies

There are actually three established methods available to manufacture a Fiber Bragg Grating. engionic Femto Gratings uses the femtosecond point-by-point writing technology, which is in all relevant aspects superior to the other technologies. The laser is focused into the core of the fiber and induces local refractive index changes in a point-by-point writing process. The process is highly nonlinear and therefore basically independent of the fiber material, which means that doping the fiber is not required. This technology makes it possible to write Fiber Bragg Gratings in almost any type of optically transparent material and through a variety of fiber coatings such as acrylate, polyimide or carbon. The gratings are type II gratings that withstand temperatures of up to 1,000°C and as the process is applied through the coating of the fiber, no stripping and recoating is required, resulting in superior tensile strength.

Draw Tower Gratings are produced by using a process that combines the drawing of the optical fiber with the writing of the grating. During the production process, the fiber crosses the optical axis of a laser and an interferometer or Phase mask that creates a periodical UV-light interference pattern in order to write the grating. Using a pulse selector and taking into account the draw speed, Fiber Bragg Gratings can positioned with a certain minimum spacing in the fiber. The coating is applied after the inscription. Another method is the strip and recoat technology, where the coating has to be removed, to allow the inscription of the Fiber Bragg Grating with an UV-Laser and a Phase mask. The coating is also applied after the inscription.