Study Of Optical Fiber Diffraction Devices Based On Helical Fiber And Their Sensing Characteristics

In recent years,with the development of optical fibers,the fiber devices have tended to become miniaturized and diversified.Helical optical fiber has attracted much attention due to its high flexibility of design,high integration,low manufacture cost,and so on.Presently,helical fibers have been widely used in communications,as acting as band-stop filters,gain equalizers,optical add-drop multiplexers and dispersion compensators,and sensors.In the sensing areas,the resonant wavelength can be shifted by changes of external parameters,such as temperature,axial strain,bending,torsion and refractive index.In this thesis,utilizing the arc discharge method,some different helical fibers are fabricated and studied.The main contents include:(1)By twisting all-solid bandgap optical fibers,optical filters with different resonant orders are realized.and the Mach-Zehnder interferometer based on dual helical all-solid bandgap fibers are fabricated.The interferometer has comb-like interference spectrum.The influence of structural parameters(interference length and helical period)is studied.It is shown that the larger the interference length is,the smaller the interference dip spacing becomes.For the sensing applications,the temperature sensitivity of the interferometer is 12.9 pm/?,the mechanical torsion sensitivity is 82.1 nm?mm/rad,and the axial strain sensitivity is-1.63 pm/?? around a wavelength of 1494.4 nm.(2)Utilizing the arc discharge method,we fabricated the helical single-mode fiber with ultra-long periods.The formed periods are 547 ?m,1068 ?m and 1497 ?m,respectively.And the induced resonant wavelength is around 1550?2 nm,namely 1549 nm,1550 nm and 1552 nm respectively.The physical mechanism is demonstrated.The measured temperature sensitivity is 69.83 pm/?,and the mechanical torsion sensitivity is-194.14 nm?mm/rad.