Photonic Crystal Fiber Axial Angle Orientation Based On Sidelobe Integral Ratio Method

The Photonic crystal fiber(PCF)has more excellent characteristics than the ordinary optical fiber,and it is widely used in sensing,materials,and other areas.The Accurate axial angle orientation of PCF has great significance in fiber manufacturing and industrial applications.In addition,the digital holography technology has advantages of no-pollution and real-time online measurement.Digital holography technology plays an important role in multidimensional object field reconstruction,biomedical science and other aspects.This thesis describes the axial angle orientation analysis of large-mode field,hybrid,endless single-mode and all-solid PCFs based on digital holographic technology.The main work is as follows:In this thesis,the theory of digital holography including digital recording and numerical reconstruction is described.In addition,the derivation of recording conditions,the comparison of three numerical reconstruction methods including Fresnel diffraction,convolutional reconstruction,and angular spectrum reconstruction are described.Axial angle orientation based on angular spectrum algorithm for obtaining the phase information requires complex algorithms and high-quality holograms.Therefore,it has strict requirements on light path and CCD.In this thesis,axial angle orientation of PCFs based on sidelobe integral ratio method is proposed.Holograms are analyzed by computing their Fourier transform.A characteristic value defined as a ratio of integrals in two regions of the spectrum is applied to distinguish the PCF.The one-to-one relationship between the ratio and angle is used for axial angle orientation.The method does not require a phase reconstruction process or a multiple-holograms joint operation to achieve a computed tomography scan of the internal refractive index distribution of the fiber.It is a simplified calculation method.The numerical simulation is performed with a mathematical model of fibers based on the geometric parameters.The off-axis digital holograms with different fiber axial angles are obtained based on calculations of the two-beam interference.Using the generated off-axis digital hologram and sidelobe integral ratio as the evaluation function,the relationship between the ratio and the axial angle of the PCF is derived.A Mach-Zehnder transmissive off-axis digital holographic optical system was built.The off-axis holograms of the large-mode field,hybrid,endless single-mode and all-solid PCFs at different axial angles were recoded,and the axial angle of the PCF was measured using the sidelobe integral ratio method.Except for the hybrid PCF,the deviations of the axial angles are less than 1°.The deviations of the hybrid photonic crystal fiber are mainly caused by the defect of the fiber sample itself,nothing to do with the algorithm,and the deviation is less than 2°.In addition,for the all-solid-state PCF,there are some differences between the experimental and simulation results.The causes of the differences are analyzed considering resolution of the microscope objective and the refractive index of the fiber.