We recently reported on a new fiber Bragg grating etched into the flat surface of a D-fiber and its potential use as a high temperature sensor. Since then we have investigated more in depth many of the characteristics that are unique due to the surface relief nature of the grating. In this paper we show that a surface relief fiber Bragg grating exhibits some significant advantages when compared to standard fiber Bragg gratings including: high temperature operation, polarization selectivity, and the ability for multi axis strain sensing. We also show the uniqueness of these gratings for bend sensing with two degrees of freedom.
We present a new type of fiber Bragg grating (FBG) in which we etch the grating into the flat surface of a D-shaped optical fiber. Instead of being written in the core of the fiber, as are standard FBGs, these surface relief fiber Bragg gratings (SR-FBGs) are placed in the cladding above the core. These gratings are a viable alternative to standard FBGs for sensing applications. In this work we describe the fabrication process for etching Bragg gratings into the surface of D-fibers and demonstrate their performance as temperature sensors. We show that SR-FBGs resist much higher temperatures than standard FBGs by demonstrating their operation up to 1100 degrees Celsius.
This paper presents a technique for enhancing the temperature sensitivity of fiber sensors. The method is based on the peculiar shape and doping characteristics of a reduced cladding index fiber. A portion of the core of the fiber is removed and replaced with a material having a larger change in index with temperature than the core material it replaces. A perturbation of the sensing material results in a change in the polarization of the light at the output of the fiber. This change is detected as a change in intensity through the use of polarizers. A temperature sensitive device is presented as an example of this type of sensing device. Initial experimental results indicate that replacing the core with polymer enhances the temperature sensitivity by at least a factor of 4. The new technique is promising as a means for incorporating a variety of sensing materials into the path of a beam traveling in an optical fiber.