Study On The Cascaded Fiber Grating Sensing Mechanism And Experiments

Cascaded fiber grating has many superior features to single grating, the cascaded fiber Bragg grating and cascaded long-period fiber grating have been widely used in filtering, communications, sensors, laser optical signal-to-noise ratio monitoring and other fields. Label free optical fiber biosensor combined with the advantages of fiber grating and no-marking. The Photonic crystal fiber has shown great specialties such as a flexible structural design, rapid real-time detection, convenient operation, high sensitivity, etc. Based on the previous research of fiber grating and biological sensing as well as an recently established optical fiber biological sensor model, this paper has carried out a theoretical research to the cascade fiber grating sensing characteristics and biological sensing characteristics, and simulate the deposition of cascading spectrum transmission characteristics of fiber grating. The feasibility of cascade fiber grating in the concentration detection has been proved in this research. The main work and innovative points are summarized as following:First of all, based on previous domestic and foreign research related to fiber grating and cascaded fiber grating, this paper has introduced the principle of solving the finite element method, illustrated the coupled mode theory and transfer matrix method and analyzed transmission characteristics of photonic crystal fiber grating through the example of long period fiber grating by using the transfer matrix method.Secondly, the paper has analyzed working principles and biological sensing principles of the cascaded long period fiber grating and fiber Bragg grating sensing system. It has simulated the transmission spectrum. It has also studied the influence of cascaded fiber gratings cycles and modulation depth on reflection spectrum and transmission spectrum.What’s more, the coating cascaded grating transmission spectrum are simulated, which has shown the influence of the length of long-period fiber grating, coating thickness and refractive index, environment index of cascaded grating on reflection spectrum and transmission spectrum.Finally, it has set up a cascaded LPG-FBG grating sensing system, found out the refractive index and temperature characteristics of the system though experimental measurements, and proved that the cascaded fiber grating sensing system has cascaded temperature compensation in concentration sensor.