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We report a novel Mach–Zehnder interferometer based on interference of selective high-order core modes in few mode fibers (FMFs). The proposed interferometer is composed of a section of FMF sandwiched between single-mode fibers with small lateral core-offsets. The theoretical and experimental results indicate that the interference patterns are coupled between core modes LP21 and LP02. Because LP21 and LP02 both reside in the fiber core, few of the guided light can propagate outside the fiber through the evanescent wave, which makes the sensor insensitive to surrounding refractive index (RI). The experimental results show that the proposed structure has a high strain sensing sensitivity of 3.35 pm/ $\mu \varepsilon $ within the range of 0–1000 $\mu \varepsilon $ at the wavelength of 1513 nm. RI insensitivity makes the device convenient for strain measurement in humid environment. [ABSTRACT FROM PUBLISHER]

We propose an S-tapered fiber Mach-Zehnder interferometer based on all-solid photonic bandgap fibers. Theoretical and experimental results reveal that the interference pattern originates from the coupling between core modes LP01 and LP11, LP01 cladding supermode. The proposed structure exhibits quite sensitive to temperature and nearly insensitive to surrounding refractive index (RI). Moreover, the temperature-strain cross sensitivity is only 0.0092 °C/ $\mu \varepsilon $ . The strain/surrounding RI responses show little impact on the temperature sensing precision. Such a structure is easy to fabricate and can be a promising temperature sensor, eliminating the RI/strain-induced cross sensitivity. [ABSTRACT FROM PUBLISHER]

A novel, compact, and simple in-line Mach–Zehnder interferometer (MZI) formed by cascading two hump-shaped tapers in a segment of single-mode fiber is proposed and fabricated. This optical fiber device has recognizable features for different bend directions while high sensitivities for ambient temperature and axial force. In the range of 0–1.2 \textm^-1 , the sensitivities of the sensor with the length of 13.4 mm are 10.224 and −4.973 nm/ \textm^-1 for opposite bending directions 0° and 180°, respectively. The responses for temperature and force of the MZI are also investigated in experiment. The results show that the shift of the dip wavelength is linearly proportional to the change of temperature or force. The sensitivities of temperature and force are 0.049 nm/°C in the range of 20 °C–80 °C and −3.643 nm/N in the range of 0–0.98 N. [ABSTRACT FROM PUBLISHER]

A novel optical fiber grating vector bending sensor head is proposed. The asymmetric characteristics are embedded in the sensor head by tilting the grating planes at increasing angles, as moving away from the center grid of the structure. A high-frequency-CO2-laser is used to fabricate the sensor head. Due to the characteristics of the asymmetric structure, the bending sensitivity for the curvature range from −2 to 0 \textm^\mathrm -1 reaches 8.53 nm/ \textm^\mathrm -1 , and for the curvature range from 0 to 2 \textm^\mathrm -1 reaches 2.82 nm/ \textm^\mathrm -1 , respectively. [ABSTRACT FROM PUBLISHER]

A novel long period fiber grating (LPFG) is inscribed in few mode fibers by CO2-laser-irradiation method. The experiment results and theoretical calculation demonstrate that the LPFGs are originated from the strong coupling between the fundamental core mode LP01 and the high-order core mode LP11. The resonant wavelength is found to shift toward the lower wavelength with temperature or force increasing, which is quite different from LPFGs fabricated in common single mode fibers. The gratings are quite sensitive to strain and slightly insensitive to temperature. Such structures are easy to be fabricate and can be promising candidates as strain sensors. [ABSTRACT FROM PUBLISHER]