Temperature Sensor Based on Highly Germanium-doped Fiber with Rounded Tip

A compact temperature sensor with highly germanium-doped fiber (Ge-fiber) is experimentally demonstrated. It is based on an in-line Michelson interferometer, which is constructed by splicing a 1mm-long, 75 mol.% GeO2-doped fiber to a single mode fiber (SMF) and fusing the tip into rounded shape. Since the differential refractive index of the Ge-fiber is much higher than that of normal fibers, length of the proposed sensor probe has been greatly reduced. The rounded surface provides as a concave mirror to enhance the reflection, thus leads to a high extinction ratio to the interference fringes. By monitoring wavelength shift of the reflection spectrum, temperature measurement was realized with a high sensitivity of 89.5 pm/degrees C, which is much higher than normal fiber based MI sensors owing to higher thermo-optic coefficient of the Ge-fiber. The advantages of the sensor are its compact size, facile fabrication and high sensitivity, which make it a potential candidate in point measurement of temperature.