Advantages Draw Tower Gratings (DTG^®)

Within the field of Fibre 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. The mechanical strength of the DTG^®s is tested by applying increasing tensile stress to the fibre until the fibre breaks. We have used a commercial material testing machine and applied the testing method of IEC 793-1 for fatigue test with three different elongation speeds of 3, 30, 300 mm/min and with 15 samples per speed. The breaking force is recorded and plotted in a diagram of relative breaking probability (Weibull plots). The mechanical strength of this fibre with an ORMOCER^®1(organic modified ceramic) coating with single pulse gratings of type one, is nearly the same as the mechanical strength of standard telecom fibres. Figure 1 below shows Weibull plots of the fibre tests.

Figure 1: Relative breaking probability of Draw Tower Gratings and standard telecom fibre.

Spliceless Arrays

The Draw Tower Grating technology allows to produce spliceless grating chains with a high number of sensor elements. The spatial distance between the gratings can vary from about 10 mm up to several meters or more. The spectral gap between two succeeding gratings is usually between 1 nm and several nm.

Type I grating arrays with more than 100 DTGs and varying wavelengths were achieved at 830 nm and 1550 nm using new developed photosensitive fibres. For the single pulse type I gratings at 1550 nm a reflectivity from 10% up to 40% was realized. At 830 nm we can reach about 10% reflectivity.

Figure 2: Two examples of optical bragg grating array reflection spectra, with 30, respectively 101 different wavelengths. Top: @ 820 nm with geometrical distances between the gratings of 10 mm and a wavelength gap of 1 nm. Bottom: @ 1550 nm with geometrical distances between the gratings of 8 cm and a wavelength gap of 0,5 nm.

Figure 3: Measured optical spectrum of a grating array with more than 30 % reflectivity of each grating (Single pulse type I gratings at 1550 nm with more than 30% reflectivity up to 40% reflectivity.)

Direct fixation

The coating that is applied on the DTGs is an Organic Modified Ceramic (ORMOCER^®1).This coating shows excellent adhesion properties to the fibre 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.

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 material composition, the DTG^® fiber has extremely low bending losses what allows to operate the fibers in configurations with low bending radii without having significant attenuation effects.

High repeatability

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.