Bragg Grating Embedded in Mach-Zehnder Interferometer for Refractive Index and Temperature Sensing

Fiber Bragg grating (FBG) embedded in a microfiber Mach–Zehnder interferometer (MZI) is presented for sensing multiparameters, such as temperature and refractive index. The MZI is constructed by splicing a short length of 40- $\mu \text{m}$ -diameter microfiber between standard single mode fibers. A millimeter long FBG is then written in the microfiber using direct point-by-point ultrafast laser inscription method. The microfiber MZI shows moderate sensitivity to ambient refractive index and temperature changes. In contrast, the microfiber FBG is insensitive to ambient refractive index change while it exhibits typical sensitivity to temperature variation. These distinct characteristics of the FBG and MZI sensors enable the simultaneous measurement of refractive index and temperature, and temperature compensation in ambient refractive index measurement.