Vectorial Analysis Of Diffraction Wave In Point Diffraction Interferometer And Research On Diffraction Element Based On Nanowire Waveguides

The rapid development of science and technology presents a major challenge to high-precision optical measurement technology and motiveates its development.As an important tool in the field of high-precision measurement,optical interferometric measurement technology plays a key role in the field of surface figure characterization of optical components,calibration and performance evaluation of optical systems.At present,the extreme ultraviolet lithography technology puts forward extremely high requirements for the control of the wavefront aberration of projection optical systems.The point diffraction interferometer(PDI)has been demonstated to be the most powerful measurement tool,which employs the nearly ideal spherical wave generated based on the principle of diffraction as a reference wave in the interferometric measurement.The PDI eliminates the need for high quality optical components as the reference optics in the conventional interferometer.Thus it breaks the limitation on the measurement accuracy brought by reference optics and provides a high-precision interferometric measurement method.The diffraction element that produces a nearly ideal spherical wave by means of light diffraction is the key component in PDI.The quality of the diffraction wave restricts the limit on the measurement accuracy.Accurate study and analysis are necessary to verify the use of the diffraction wave as a high-quality reference wave in interferometric measurement.Theoretical analysis and practical applications both indicates that there exist a series of problems and defects in the present diffraction elements,which limit the application and expansion of the PDI.Aiming at the problems and defects mentioned above,this thesis has carried out the vector analysis of the diffraction wave in the PDI and the research of the diffraction element based on nanowire waveguidesIn the existing method for the analysis of diffraction wave,usually only the major component of the diffraction wave in far-field are considered,and the wavefront error is analyzed with Zernike polynomial fitting.These methods are difficult to perform high-precision analysis of the diffraction wave.A framework of full-vector methods for the analysis of diffraction wave is established,which provides a reliable theoretical basis and method for the high-precision analysis of diffraction wave in PDI.The method adequately considers the vector nature of light with sufficient rigor and wide versatility.First,the propagation behavior of light in the diffraction element is simulated with the numerical calculation of electromagnetic field to obtain the diffraction wave in near-field.Then the diffraction wave in far-field can be calculated from the diffraction wave near-field based on the vector diffraction theory.Finally,the quality of the diffracted wave is analyzed with high precision.The spherical coordinates is adopted to deal with the electric field component to accurately analyze the polarization properties and amplitude distribution of the diffraction wave,and the best-fit sphere is implemented to remove the deviation between the spherical surface for the calculation of the diffraction wave in far-field and the best-fit sphere for the accurate extraction of the wavefront error of the diffracion wave.The pinhole is the most used diffraction element in PDI,whose existing vector analysis is based on the numerical method of the electromagnetic field.The thesis based on the waveguide theory and uses the analytical method to accurately and comprehensively analyze the pinhole diffraction problem.This method gives the same conclusions with the numerical method of electromagnetic field in many aspects,but brings a more profound interpretation of the physical mechanism behind the characteristics of diffraction wave,which is important for the accurate analysis of pinhole-diffracted waves.The pinhole on the metal film is discussed,which acts as a circular metal waveguide to transmit light field.The incident light is focused on the front surface of the pinhole,a part of which is reflected while other is coupled into the pinhole.The light field is transmitted in the pinhole in the form of mode and emitted at the end to generate a diffraction wave.Due to the cut-off effect of the waveguide,when the size of the pinhole is too small,the energy transmittance decreases sharply obtaining no effective diffraction wave.The light in the pinhole is transmitted in the form of mode which also determines the properties of the diffraction wave.Based on the analytical solution of the mode conducts a comprehensive analysis of the properties of the pinhole diffracted wave is given.The diffraction wave is elliptically polarized light with an eccentricity close to 1.The intensity and phase distribution of the diffracted wave are rotationally asymmetrical,and the main aberration is primary astigmatism.This is caused by the non-rotational symmetry of the mode caused by the interaction between the optical field and the pinhole waveguide.This has important guiding significance for the analysis and design of the pinhole diffraction element in PDI.The existing diffraction elements have a series of defects.The diffraction waves of the optical fiber diffractive have a small numerical aperture,while the diffraction waves of pinhole are easily interfered by the wave aberrations,alignment errors of the incident light and other factors,and the light intensity is relatively weak.In view of the above problems,finding a better alternative is a problem of interest.The thesis innovatively applies the micro-nano optical waveguide to the diffraction element in PDI,and carries out theoretical analysis and researchof the diffracton wave of the micro-nano fiber and nanowire waveguide.Based on the FDE method,the mode in the micro-nano optical waveguide is solved and its transmission characteristics are analyzed.The diffraction wave is solved by the vector diffraction theory,and the quality of the diffracted wave is analyzed and studied.The micro-nano optical waveguide has the characteristics of small cross-sectional size and large refractive index difference between the core and cladding,so it has a strong optical field confinement ability.As a diffraction element,it has outstanding advantages.First,the micro-nano optical waveguide can obtain sub-wavelength light field cross-section,thereby diffracting a spherical wave with a large numerical aperture which is significantly improved compared to traditional diffraction elements.Secondly,the single-mode condition brings excellent filtering ability of the incident light for generating stable diffracted waves.Finally,the wavefronts of the diffracted waves of the micro-nanooptical waveguide have high sphericity,which provides an important basis for its use as the diffraction element in PDI.The diffraction wave of the nanowire waveguide has excellent properties.In order to apply it to PDI,it is necessary to analyze and design the bending loss,coupler and other structures.In view of the above problems,the thesis proposes and designs a diffraction element based on the nanowire waveguide,and completed the processing and production of the diffraction element.First,the bending loss in the nanowire waveguide is analyzed for the design of the bending curvature.Secondly,the Y branch coupler is selected and optimized on its structural parameters to improve the coupling efficiency and provide a stronger diffraction waves.Finally,the nanowire waveguide processing technology is explored,and the production of diffraction elements based on nanowire waveguides is completed,and a diffracton wave with a larger numerical aperture is obtained.