Single-Mode–Multimode–Single-Mode Optical Fiber Sensing Structure With Quasi-Two-Mode Fibers

This paper reviews some aspects of optical fiber sensors based on a single-mode (SM)-multimode (MM)-SM structure and reports on the realization of temperature sensors in which the MM section is made by a quasi-two mode fiber. Two different realizations are compared that rely on: 1) a bend-insensitive fiber operated in the second optical communication window and 2) an SM fiber at 2 μm operated in the third optical communication window. The performances of the sensors are compared with those of similar structures that exploit largely MM sections.