Within the field of Fiber Bragg Grating sensing, Draw Tower Gratings have some unique properties what makes them the preferred product for many FBG applications. These are:
Extremely high mechanical strength
Draw Tower Gratings show extremely high mechanical strength compared to conventional produced gratings as is shown in Figure 1. The mechanical strength of DTG®s and standard recoated FBGs is tested by applying increasing tensile stress to the samples until the fiber breaks. The test has been performed using a commercial material testing machine according to IEC 793-1 and consists of a fatigue test with three different elongation speeds of 3, 30, 300 mm/min. 15 samples per speed were tested. The breaking force is recorded and plotted in a diagram of relative breaking probability (Weibull plots).
As can be observed from Figure 1, the mechanical strength of the DTGs® 's is nearly five times higher compared to classical recoated FBGs.
Figure 1: Relative breaking probability of Draw Tower Gratings and standard telecom fiber.
The Draw Tower Grating technology allows to produce spliceless grating chains with a high number of sensor elements. Figure 2 shows the spectrum of an array of 80 DTGs on a single fiber, all with a varying wavelength.
Figure 1: Spectrum of a DTG array containing 80 different wavelengths.
The coating that is applied on the DTGs is an Organic Modified Ceramic (ORMOCER®1). This coating shows excellent adhesion properties to the fiber glass, which makes DTG®s directly applicable for fixation on structures without coating removal. This does not only facilitates the installation process, but also increases the reliability.
Uniform coating coverage
The coating is applied after the writing of the DTG. No stripping and recoating process is therefore needed anymore. DTGs have therefore the unique property that the coating is uniform over the full lenght of the fiber, even on the position of the DTGs itself.
High operating temperature range
The coating of the DTG®s is the factor that limits the temperature operating range. DTG®s are coated with ORMOCER®1 material and therefore temperatures between -180 and +200°C can be applied.
Low bending loss
Due to the used glass composition, the standard DTG® fiber has extremely low bending losses what allows to operate the fibers in configurations with low bending radii without having significant attenuation effects.
DTG®s are fabricated using an automated production process. This process allows to control the production parameters very accurately and assures high repeatability and quality.
Relatively low cost
Due to the fact that the DTG®s are produced using a full automatic production process, they can be produced at a rather low cost, especially for medium and high volume orders.
1ORMOCER® : Trademarkt of Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.