Study of temperature sensor fiber with high germanium doped core

In the present work, the use of a single mode fiber (SMF) with high Germanium doped core as temperature sensor is studied. The fiber core consists of a 1.1 μm highly germanium doped step index waveguide surrounded by a pedestal of 3.5 μm diameter. The outer diameter of the fiber is 125 μm. A short stub of ~2 mm is used in the fabrication of the interferometer. The highly germanium doped fiber is spliced between two standard SMF. In one of the splices both fibers are ideally aligned, in the other splice a small misalignment between the fibers is done. An annealing process is made for 5 hours at 850°C which results in a good operation stability up to 700°C. A wavelength shift as a function of temperature of 76 pm/°C is reported. To demonstrate the interferometer efficiency, a fiber Bragg grating is written in the highly germanium doped core and tested for temperature response. A temperature sensitivity of 13pm/°C was demonstrated. The interferometer fabrication requires only a few and easy steps. Due to the standard splices made between the fibers, the device is robust. We believe that the sensor may be used under harsh environmental conditions, since it shows a high sensitivity and a small size in combination with great robustness.