Side-polished Fiber Bragg Grating And Its Sensing Properties To Study

Recently, the optic fiber grating has gotten extensive applications in the fiber optic communications and sensors. It has become an important device in these two fields. Because the optic fiber grating is compact, simple in fabrication, it has been used in the sensing of the stress, temperature and other physical quantities. The optic fiber grating sensors can be operated in wavelength-coding manner and it is sensitive to the wavelength. In addition, the optic fiber grating sensors have advantages of linear response, easy to integrate, and low input loss. But by the characteristics of the optic fiber grating, the optic fiber grating is not sensitive to the external refractive index and cannot be directly used as gas or liquids sensors without the intermediate material like hydrogel. In this thesis, based on the technique of optic fiber grating sensor and side-polishing method, the D-shaped fiber Bragg grating concentration sensor is studied and the experimental results are analyzed.By side-polished, the cladding layer of one side of fiber Bragg grating can be reduced to several micrometers. The radiation field can transmit the cladding layer to external medium. When the external refractive index changes, the effective refractive index of fiber changes and the center wavelength of D-shaped fiber Bragg grating shifts accordingly. Compared with D-shaped fiber, the D-shaped fiber Bragg grating index sensor is more precise and reliable because the sensed information is encoded into wavelength, which is an absolute parameter, the output does not depend on the light levels, loss in the connecting fibers and couplers, or source power.In this thesis, we make D-shaped fiber Bragg grating by side-polishing technique. Then, we use the D-shaped fiber Bragg grating to carry on the concentration sensing experimental of NaCl solution and glycol solution and the experimental results are analyzed.