SMS Fiber Sensor Utilizing a Few-Mode Fiber Exhibits Critical Wavelength Behavior

We experimentally demonstrate the existence of a critical wavelength in the 1.4-1.6-μm optical communication window for the single-mode-multimode-single-mode (SMS) fiber sensor utilizing a few-mode fiber (FMF). Peaks near the critical wavelength exhibit higher sensitivity to temperature or strain. A theoretical analysis of this SMS structure shows that the critical wavelength behavior is mainly governed by the fiber refractive index (RI) profile with no significant effect from material dispersion. There is only one critical wavelength in the range where the LP₀₂ mode of the FMF is supported. Small alterations of the fiber RI profile can tune the critical wavelength.