The Theory And Application Of Overlapping Cascade Long-period Fiber Grating

As the long-period fiber grating has the advantages of low production cost, accuracy and easy to be made, no backward reflection and multiple environmental parameters sensitive, it plays an important role in a variety of optical devices production, and has always been one of the hotspots of optical communication, optical sensing and other fields.Cascaded long period fiber grating as a special form of long-period fiber grating, whose transmission spectrum, compared to a single long period fiber grating, can be controlled more flexible, has a wider range of applications. In this paper carried two overlapping characteristics and application of long-period fiber grating cascade, major progress and completion of the work are as follows from theoretical studies and simulation analysisIn this paper, having carried out characteristic and the application of two overlapping cascade long period fiber grating by theoretical research and simulation analysis. The main progress and completion of the work are as follows:(1) Using the basic theory of three-layer fiber model, the coupling constants and effective refractive index of the core mode and cladding modes are solved. Analyzing the mode coupling principle of overlapping cascade long period fiber grating, the transmission spectrum of overlapping cascade of two long-period fiber grating is obtained by numerical simulation.(2) In this paper, we analyzed the band-stop filter characteristics of overlap cascaded long period fiber grating. Besides, we studied how the coupling constants between the core mode and cladding mode, the length and period of the long period grating affect filtering performance through simulation. It provides guidance for optimizing the parameters and achieving the desired band-stop filter performance.(3) Studying the environmental characteristics of the refractive index detection by using overlap cascaded long period fiber gratings, analyzing the relationship between the resonance wavelength and the period of long period fiber grating. The results show that different resonance wavelengths performance different drift directions when the environment refractive index changes. We optimized the design of the cladding mode order and its corresponding resonance wavelength to achieve high sensitivity to the environment refractive index of the overlapping cascade long period fiber gratings. It indicated that when the environmental index of refraction in the range of 1.3to1.42,the detection sensitivity is up to546nm/R,U～2187nm/RIU.