Utilising a loop structure to allow a microfiber coupler with larger taper diameters to be used for sensing

This paper examines a technique that utilizes a Sagnac loop with a microfiber coupler (MFC) as a coupler which allows the MFC to operate effectively as a sensor but with larger than normal tapered fiber diameters. The proposed structure is found to be suitable for temperature and refractive index (RI) sensing. It is shown that a variation in the surrounding of the MFC RI results in a shift of the output spectrum, while a temperature variation leads to changes in the intensity of the interference dips. A decrease in the waist diameter of the MFC results in an increase in the sensitivity to temperature. For MFC structures based on a 5.6 μm and a 3 μm fiber waist diameter, the minimum transmission power level of a selected spectral dip decreases by 1.7 dB and 5.03 dB respectively, as the temperature changes from 18 °C to 44 °C. A change in the surrounding RI from 1.334 to 1.395 results in the spectral redshift of 8 nm using a 5.6 μm fiber waist diameter. By functionalizing the surface of the MFC with various materials, the structure could potentially be used for sensing of other parameters.