Simultaneous twist angle and direction sensing using abrupt-tapered fiber Mach-Zehnder interferometers

We demonstrate wavelength-tunable abrupt-tapered Mach-Zehnder interferometers (AT -MZI) with the extinction ratios of above 32 dB by introducing two points of abruptly tapering in a short length (<; 1.4 cm) of highly Er/Yb co-doped fiber (EYDF). The EYDF is immersed in a micro flame where the bilateral edges of flame can provide a higher heating temperature than that of the inner portion part. Thus the abrupt tapers can be made when the two heated points are suddenly pulled away in the opposite directions. The abrupt tapers can help the excitations of cladding modes deriving from the core mode and the interference occurs when the phase difference between core and cladding modes are satisfied after a certain propagation length. By forward twisting the leading fiber of the AT-MZI, the resonance wavelengths move toward the shorter wavelengths for more than 6.4 nm (from 1621.6 to 1628 nm). The wavelength between 1343.6 nm and 1345.6 nm, we found that the opposite twist directions in few twist angles can have wavelength shifts.