DTG^® - Draw Tower Grating Principle

Draw Tower Gratings (DTG^®) are produced with a process that combines the drawing of the optical fibre with the writing of the grating.

The figure shows the set-up of this production process. The input of the process is a photo-sensitive pre-form. By heating the pre-form, the pulling and formation of the fibre will be initiated. Further down in the production process, the fibre crosses the optical axis of an excimer laser and the interferometer 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, FBGs can be written on well-determined places in the fibre. When the grating has been written the fibre is coated by entering a liquid coating reservoir, followed by an UV-curing of the coating. Finally the location of the FBG is marked automatically and the fibre is reeled on a drum.

This process of simultaneously drawing the fibre and writing the grating results in high strength grating chains. This is caused by the fact that the coating is applied after the grating has already been written and so the commonly used stripping and recoating process as with standard FBG production is not needed anymore. The fresh and clean glass surface is therefore maintained during the fibre drawing pocess.