Analysis Of Point-Diffraction Wavefront With Sub-Wavelength-Aperture Fiber

Based on the fiber with sub-wavelength aperture,the point-diffraction wavefront with both high numerical aperture(NA)and high power is obtained,by which the poor light power of pinhole point diffraction wavefront and the small aperture angle of single-mode fiber point diffraction wavefront can be solved.In addition,misalignment aberrations of point-diffraction wavefront introduced by point source space are effectively corrected and point-diffraction wavefront is reconstructed.The main content of this dissertation include:The point-diffraction wavefront based on the finite difference time domain(FDTD)method is analyzed,and the effects of various factors such as aperture,cone angle,film thickness of sub-wavelength-aperture fiber and NA on point-diffraction wavefront error,aperture angle,light transmittance and intensity uniformity are discussed in detail.The simulation demonstrates the feasibility of high NA and high power of point-diffraction wavefront with sub-wavelength aperture fiber,an aperture angle about 90° and light transmittance about 29% can be obtained with 0.5?m sub-wavelength fiber aperture.The misalignment aberrations of point-diffraction wavefront introduced by point source space are analyzed,and calibration techniques which are available to high-precision and high NA spherical surface are presented to calibrate the misalignment aberrations no matter point source space and NA are known or unknown.The computer simulation is carried out to demonstrate the feasibility of the proposed calibration method.A precise reconstruction technique based on the difference Zernike polynomials is proposed to reconstruct the point-diffraction wavefront,the effects of traditional calibration technique and proposed calibration technique of misalignment aberrations,point source space,NA of spherical surface and the distance of point source to detector on reconstruction technique are discussed.An experimental,sub-wavelength aperture fiber point diffraction interferometry system has been established.The testing experiments for the light power transmittance and aperture angle of sub-wavelength-aperture fiber and single-mode fiber point diffraction wavefront have been carried out.The feasibility of the proposed calibration method of misalignment aberrations introduced by point source space has been demonstrated with the experimental testing results.