Device Design Based On Long-period Fiber Grating In Embedded-core Fiber

In this paper,the long period fiber gratings(LPGs)and their coupling principle are studied.The methods of writing LPGs are introduced and the advantages of using the point by point writing method of high frequency CO2 laser,specific steps,precautions are illuminated.In addition,the LPGs was wrote on embedded-core optical fiber(ECOF),and based on this long-period fiber grating in embedded-core fiber(ECOF-LPG),Mach-Zehnder Interferometer in embedded-core fiber(ECOF-MZI)and flexural ECOF-LPG were designed and fabricated and their sensing characteristics were measured and analyzed.Firstly,a grating writing system was set up according to the experimental design.The high-frequency CO2 laser was used to write the LPG on the ECOF successfully.The sensing characteristics of ECOF-LPG samples were measured.The advantages and disadvantages of ECOF-LPG were compared with traditional single-mode LPG.The forming principle of LPG is introduced in detail.The theoretical analysis of ECOF-LPG was carried out by the combination of finite element analysis and numerical calculation.The resonance peak is determined by the coupling of core mode LP01 and cladding mode LP91.Then,ECOF-MZI was designed and prepared according to LPG's grating principle.The influence of the grating distance on the transmission spectrum of the sample was studied.The three-peak sample's characteristics were measured and analyzed.The experimental results show that the new optical fiber device behaves similar to the traditional single-mode LPG in both temperature and stress.The refractive index measurement is divided into external and internal part of the sample,the sample is insensitive to the external refractive index,but its internal refractive index performance has a very large potential application value.Finally,the design and preparation of an anti-bending ECOF-LPG was completed,the measurement results show that this anti-bending ECOF-LPG can be better immune to bending effect on the transmission spectrum,laying a foundation for the development of new optical fiber devices.