Study On Sensing And Demodulation Technology Of Tilted Fiber Bragg Grating

Fiber grating is a passive optical component with a grating formed by periodical refractive index modulation grating of fiber core using fiber photosensitivity. At present, fiber grating has been widely used in temperature, stress, pressure and other parameters sensor measurement. Tilted fiber Bragg grating(TFBG), a new fiber grating whose grating has a certain angle perpendicular to the fiber axis, not only has all the features and benefits of fiber Bragg grating, but has the external environment refractive index sensitive characteristics of long-period fiber grating (LPG), which can be used for multi-parameter measurement, so TFBG can solve cross sensitive problem effectively.We firstly described the basic concept and classification of fiber grating, emphatically expounded the research progress of TFBG sensor and demodulation technology, on this basis, we made comparison and selection to demodulation scheme. Then we described the coupled model of TFBG and investigated its temperature, stress and refractive index sensing characteristics by theoretically and experimentally.With comprehensive analysis based on the research of the performance characteristics of various existing demodulation methods, we selected the combination of volume phase diffraction grating and InGaAs materials PIN diode detector array as the hardware part of demodulation scheme, and selected the Bayspec spectrum demodulation module (FBGA) base on above scheme and the host computer software as software part of demodulation scheme, and build a demodulation system. According to the TFBG sensing characteristics, we prepared the host computer software contains three detection parameters of temperature, stress and refractive index to realize the data measurement、processing and results display function of temperature、stress and refractive index based on tilted fiber Bragg grating sensors. According to the cladding modes characteristics of TFBG, a new refractive index demodulation algorithm of calculating the wavelength between cladding modes and ghost mode was proposed. The method can rapidly and accurately detect SRI whose value ranges from1.40to1.45. Temperature, stress and refractive index sensing measurement experiments showed that the cladding mode of TFBG was sensitive to refractive index but immune to temperature and stress, using the characteristic of tilted fiber Bragg grating, we can realize two-parameters measurement of temperature-refractive index or stress-refractive index.