Packaging of surface relief fiber Bragg gratings for harsh high temperature environments

The Surface Relief Fiber Bragg Grating (SR-FBG) is a viable alternative to the thermocouple for high temperature measurements in industry. To fabricate the SR-FBG we etch a grating into the flat surface of an elliptical-core D-fiber. At high temperature (1000 °C) the optical fiber becomes brittle. To overcome brittleness we thread the fiber through a preheated 0.020 inch diameter stainless steel tube. We insert the small tube into a larger one with a diameter of 0.125 inches. The smaller tube rests on ceramic inserts to prevent contact with the large tube. The end of the D-fiber is fitted with a standard fiber optic connecter. With this packaging scheme we conduct a series of test at high temperature. The sensor is robust with no power loss or Bragg wavelength shift, even after heating for 24 consecutive hours.