The effects of geometric design on the performance of abrupt-tapered fiber Mach-Zehnder interferometers

We investigate the influence of taper geometry in Er/Yb co-doped fiber (EYDF) strain sensors using tunable abrupt-tapered Mach-Zehnder interferometers (AT-MZI). It was found that the sensitivity of the strain sensor can be enhanced by reducing both the waist diameters of, and the span between the two abrupt tapers. For strains under 0.2% in AT-MZIs with a consistent span of 10 mm, the strain-induced interference wavelength shift increases from 0.5 nm to 8.4 nm as the average waist diameter of the two abrupt tapers decreases from 62.58 μm to 24.58 μm. Those AT-MZIs with a greater span between the abrupt tapers or a greater difference between the two taper waist diameters display a decreased sensitivity. It is also shown that the span between tapers in inversely proportional to the free spectrum range and the extionction ratio.