In-Fiber Mach–Zehnder Interferometers for Sensing

In-fiber Mach–Zehnder interferometers (MZIs)In-fiber Mach-Zehnder Interferometers are based on the interference between two light beams transmitted in the functional optical fiber. They have the advantages of compact structure, high sensitivitySensitivity, resistance to electromagnetic interference and most importantly, the flexibility to construct with different kinds of fibers and materials. Several methods, including the splicing method, the femtosecond laser inscribing method, the microtapering method and the macrobending method can be utilized to fabricate the in-fiber MZIs. The various advantages as well as different manufacturing methods allow the in-fiber MZIs to flourish in the sensing application areas. They are applied for the measurement of temperature, strain, curvature, refractive index (RI) as well as other measurands such as humidity, magnetic field and the concentration of gas and metal ions. In this chapter, the basic principle and sensing mechanism of the MZIs for the measurement of these measurands are presented and discussed. In addition, recent progress of in-fiber MZIs for these sensing applications is reviewed. Specifically, the means to enhance the sensitivities are summarized and discussed. The chapter starts with the fundamental principle and fabrication methods of in-fiber MZIs. Then, the sensing mechanisms and experimental studies of the in-fiber MZIs proposed for different measurands are reviewed. Finally, a summary of the whole chapter and a prospect for the development of the in-fiber MZI sensors are given in the conclusion part.