Fiber M-Z Interferometer Based On Asymmetric Modulation

In recent years, with the rapid development of economy and society, food, environment, engineering detection has becoming more and more important in the social development processing, the development of new type of sensor has became a popular research in academia and engineering. To be a part of the new type sensors, the optical fiber sensors for their compact, anti-electromagnetic interference, high sensitivity, fast response, easy to reuse and remote sensing and many other advantages, has been applied in many fields. The fiber Mach-Zehnder interferometer?MZI? is the main form of application, the principle of MZI is the use of required parameters to change the phase between the sensing signal arm and the reference arm, and then use the demodulation technique to obtain the required sensing parameters of the actual information. Optical fiber, for the light transmission media, sometimes can integrate two paths in a single optical fiber, which makes optical fiber MZI to become more compact and cheap.In this paper, for the respect of asymmetry refractive index modulation, we have proposed and fabricated two new type fiber MZI, with introducing spatial non symmetry, MZI has the ability of sensing space vector bending and torsion, and the characteristics of MZI spectral were analyzed and validated in experiment and theory. We have optimized their structure, improve the sensing performance of MZI.1. For the first time to our knowledge, a bending vector sensor based on an SLPFG interferometer has been experimentally demonstrated. The sensitivity of the sensor reaches 8.53nm/ m^-1at the curvature range of-2.0 m^-1 to 0 m^-1, and 2.82nm/ m^-1 at the curvature range of 0m^-1 to 2.0 m^-1. Compared with other published structures, the proposed structure possesses several advantages such as simple structure, compactness, easily fabricated, and it overcomes the shortcoming that the conventional LPFG is insensitive to bending for the curvature range of-0.5 m^-10.5 m^-1.2. The SLPFG interference model is established. The interference spectrum of common long period fiber grating?LPFG? is compared with the interference spectra of different tilt angle SLPFG. The refractive index modulation depth of LPFG and SLPFG is calculated, and the interference mechanism of 4 degree SLPFG is analyzed. The reason of the non-symmetric sensitivity of SLPFG bending sensitivity is explained in theory.3. For the first time to our knowledge, a torsion sensor with directional discrimination based on a twist taper in polarization-maintaining fiber has been experimentally demonstrated. The torsion sensitivity for the twist rate from 0 rad/m to 8 rad/m reaches 1.071 nm/rad·m^-1, and for the twist rate from 0 rad/m to-8 rad/m reaches 2.392 nm/rad·m^-1, respectively.4. We have established the interference model for the twist taper on polarization maintaining fiber, and analyzed the different torsion responses of the different interference peaks, the torsional responses has been theoretical calculated, which is good consistent with the experimental.