Draw Tower Gratings (DTG®s) are produced using a process that combines the drawing of the optical fiber with the writing of the grating.
The figure below shows the set-up of this production process. The input of the process is a glass pre-form. After heating the pre-form, the pulling and formation of the fiber will be initiated.
Further in the production process, the fiber crosses the optical axis of a laser and the interferometer that create a periodical UV-light interference pattern in order to write the grating. Using a pulse selector and taking into account the draw speed, FBGs can be accurately positioned in the fiber.
When the grating has been written the fiber is coated by entering a coating reservoir, followed by a-curing step of the coating.
Finally the location of the FBG is marked automatically and the fiber is reeled onto a drum.
This process of simultaneously drawing the fiber, writing the grating and coating the fiber directly after the grating inscription, results in high strength grating chains.
As such the commonly used stripping and recoating process of standard FBGs is not necessary and the pristine fiber strength is maintained during the DTG® manufacturing process.