Research On Fiber Sensor Based On The Spherical-shape Structure Of SMF

Compared with the traditional electric sensor, optical fiber sensor has many unique advantages, especially working in the harsh conditions. Optical fiber sensor has become hot spot of research in the field of sensor. In this thesis, a fiber sensor based on spherical-shape single-mode fiber is designed which is fabricated by a commercial fusion splicer, and is capable of measuring a variety of parameters. The new fabricated spherical-shape structure can induce the variation of light transmission in fiber. Therefore, the transmission spectral is easily affected by external environment change. The appearance of spherical-shape single-mode fiber provides new ideas for the fabrication of fiber sensor, and also has great application value in the tunable fiber lasers.The main content of this thesis includes:1. The research background of optical fiber sensor and several common interferometric sensors are firstly introduced, and the research status and sensing properties of several mode field mutations structures(such as core-offset structure, tapers, mode mismatch, etc.) have been explained.2. A new fabrication of spherical-shape single-mode fiber is proposed, and the principle of it is analyzed. Due to novel, simple, and low cost, the fabricated spherical-shape structure has potential application value.3. A cascade two spherical-shapes optical fiber sensing structure is proposed, and the principle of it is analyzed. When different lengths between two cascade spherical-shape structures are chosen, the transmission spectral is compared and can be used to analyze sensing characteristics when measuring temperature, strain, micro displacement and liquid level.4. By cascading a fiber Bragg grating with two spherical-shape structures can realize temperature and liquid level double parameters measured simultaneously.5. A reflective sensor structure based on a spherical-shape single-mode fiber cascaded with a fiber Bragg grating is proposed. Sensor can observe the core mode and cladding mode of fiber Bragg grating reflection peak. When external environment, such as temperature, micro displacement, and refractive index changes, the variation of reflection spectrum is researched from two aspects: wavelength shift and intensity change.