Research On Demodulation System Of Optical Fiber Current Sensor Based On Slow Light

Fiber Bragg Grating (FBG) sensor is a new type of fiber-optic sensors, which has developed rapidly in recent years. Because of its advantages such as anti-disturbance of electromagnetism and easy attaching to the measured external parameters, many sensing characteristics and structures of FBG have been extensively researched and applied. Based on the thorough study of the fiber Bragg grating sensor and slow-light technology, slow-light technology was proposed to be applied to fiber Bragg grating sensing system, which can improve the sensitivity of the fiber Bragg grating sensing system by increasing the wavelength demodulation sensitivity. The research contents of the paper are introduced as following:(1) An isosceles triangle cantilever-based FBG current sensor unit was proposed. Firstly theoretical modeling and simulation analysis were made, which found the relationship between the current and offset of the center wavelength of FBG reflection, and simulation analysis according to the selected actual situation parameters was carried out. Experimental results showed that the current change and the fiber Bragg grating central reflected wavelength change were in a linear relationship. The maximum error was0.04A, and the error average0.019A with the current detection sensitivity0.290nm/A when the current is0-2A.(2)The all-fiber M-Z interferometer was adopted for demodulation of FBG wavelength signals, and the optical fiber interferometer demodulation experiment was made. Firstly fiber M-Z interferometer demodulation principle was derived, and the influence of the fiber coupler splitting ratio to the interferometer output characteristics was studied by simulation, obtaining that interferometer output visibility was maximized under the conditions of3dB coupler. At the same time, the effect of the interferometer arm length difference on demodulation was researched, getting the relationship between arm length difference and demodulation range. Before the experiment, the interference spectrum of fiber M-Z interferometer was first got by using the wide spectrum light source for arm length difference determination, and experimental results demonstrated that the resolution of the fiber grating wavelength reached2pm.(3) The improvement of M-Z interferometer wavelength demodulation sensitivity after the introduction of slow light was discussed, and simulation verified that photonic crystal waveguide slow light made the MZ interferometer sensitivity greatly improved, and the specific increment related to the group index of photonic crystal waveguide chosen. In this paper, simulation results show that the demodulation sensitivity of optical fiber M-Z interferometer based on photonic crystal waveguide slow light can be improved more than10times.In this paper, the proposed new method, which combined slow light technology with optical fiber Bragg grating current sensor technology, achieves the desired design requirements.