IntroductionSMSfiber structure is extensively investigated by the scholars allover the world. The output spectrum of the SMS is modulated tocarry the information of the change of the multimode fiber (MMF).Thus, when the MMF is affected by the variation of certain param-eters, such as the temperature, strain and refractive, the length,curvature or distribution of the silica fiber refractive index (RI), allmay change to shift the transmission spectrum. And then the mea-surand could be obtained via the one to one relationship betweenthe spectral shift and measurand variation.For example, utilizing the modal interference to measure tem-perature is based on the thermo-optic effect and the thermalexpansion effect which change the length, diameter and refractiveindex of the MMF. And then the output spectrum will shift [1,2].As measuring strain, the stress is applied on the longitudinal ortransverse to bend the sensing fiber and the fiber is twisted anddeformed. Due to the mechanical principle and the photoelasticeffect, the output spectrum shifted [3–5]. And the curvature mea-surement is similar to the strain measurement except for applyingthe stress transversely on the middle of the sensing fiber [6,7].