Two curvature sensors based on no-core–seven-core fiber interference

Using the no-core fiber (NCF)–seven-core fiber (SCF) interference structure, two curvature sensors of Michelson interference type and Mach–Zehnder interference (MZI) type are proposed, respectively. The curvature sensor based on Michelson interference shows wavelength-modulation characteristics, the sensitivity is about −22.76 nm/m−1 with a linearity of 0.9823, the temperature sensitivity is only 0.054 nm/°C, and the effect of temperature on curvature can be negligible. The MZI sensor based on an enlarged taper-embedded cascaded structure is an intensity-modulated sensor. The sensitivities are −63.6271 dB m/m−1 and 93.3293 dBm/m−1 for the forward and reverse curvature, respectively, and the linearities are 0.9987 and 0.9930, respectively. But the strain sensitivity (8.357 × 10−4 dBm/με) of the MZI sensor is so tiny, which can avoid the strain cross effect. The two sensors can be used in the detection of the curvature at different (temperature/strain) conditions.