Novel Bragg grating fibers for strain and temperature separated sensor systems

Fiber Bragg gratings (FBGs) are commonly used as sensing elements in optical fiber sensors, as filters in optical communications systems as well as laser cavities in all fiber lasers. In the case of fiber-optic sensors the FBGs can be used directly to measure strain and temperature simultaneously with very high accuracy. One drawback of using any commercial standard FBG sensors is the superimposition of the strain and temperature generated Bragg wavelength change, resulting in the need of additional sensors to realize temperature compensation. To overcome this disadvantage a method of separating strain and temperature by the use of enhanced birefringent Bragg grating fibers was developed. The fabrication of the specific draw tower gratings (DTG) is based on the combination of several innovative manufacturing methods. To these belong the preform preparation by stack-and-draw technique as well as the fiber drawing process including the generation of the DTGs by laser inscription and will be shown in detail. Furthermore we will discuss the temperature and strain properties of these special FBGs and present successfully separated several diversified temperature and strain progressions.