Research On Analysis And Experiment Of Some Micro-Nano Devices’ Optical Properties

Human society has entered the high-speed information age. The devices which are needed in both civil and military fields have a tendency to miniaturization and integration. The manufacture and application of micro-nano structures has become a hot research point. Micro-nano optical structures have very important applications in the micro optics, and with the development of micro optics, more and more micro-nano optical structures have been designed, manufactured and used. In the optical properties analysis of the micro-nano structures, traditional geometric optics and scalar diffraction theory are no longer applicable. The vector diffraction theory must be applied. In this thesis, the finite difference time domain (FDTD) method was used to analysis the optical properties of the fiber probe, optical microsphere cavity and antireflection structure. The polarized laser direct-write technology is used to inscribe the binary micro-nano structures and the generation and focusing of azimuthally phase-delay cylindrical vector beams is studied.The main research contents of this thesis are listed as follows:1. The brief introduction of the FDTD method is presented. The Fortran is used to build the3D computer program, and the reliability of the absorbing boundary conditions is verified. The FDTD in the metal is presented. The significance of the probe polarization characteristics is analyzed. The light intensity distribution near the optical fiber tip is calculated with linear-polarized incident light. A general relationship between the extinction ration and the probe varying with its relevant parameters has been found by means of making alternations on the aperture diameter, cone angle, thickness of metal film and material as well as incident light wavelength and other parameters. The results show that the above multi parameters have produced a co-effect on the polarization characteristics of the optical fiber probe.2. The2D optical computing equivalent model of the microsphere cavity is built. The resonance performances of three-layer and four-layer microcavities with waveguide are analyzed, respectively. Comparison of the homogeneous, two-layer and three-layer microcavities, the three-layer microcavity has the highest maximum energy density, stored energy and the smallest mode volume. An optimal gap dimension between the three-layer microcavity and the waveguide exists; the optimal gap of the model in the paper is60-120nm. A microcavity which has better performance with particular wavelength can be got by varying the middle layer’s thickness or refractive index. The microcavity with an output waveguide was analyzed with the Gaussian beam excitation. The frequency spectrum in the output waveguide was similar to that in the mircocavity. It shows that the three-layer microsphere cavity can achieve frequency-selecting and light-export. If the four-layer microsphere has an appropriate second layer thickness, the inner and outer resonances are independent to each other and both have a higher stored energy. The external refractive index change only produces an effect on the outer layer’s resonance characteristics, but not on the inner.3. Several analysis methods of the grating are introduced. The FDTD periodic boundary condition is built based on the Floquet theory and dual plane wave. The computer program (TM/TE) of the1D periodic structure is built, and the reliability is verified. The electromagnetic scattering problems of the periodic structures include grating can be simulated through changing the shape and media in one unit. If increase the height of tapered grating or reduce the period width, the grating transmittance will increase. But for the TE wave, need to pay attention to the oscillation if reduce the width. The qualitative simulation of the grating transmittance under a certain wavelength can be got by using the ratio between the wavelength and the height and width.4. Polarization laser direct-writing system is designed and introduced, include mechanical and electrical part, the laser polarization modulation part and the software. Binary micro-nano structures, such as grating, graphics and zone plate, have been inscribed on the azobenzence polymer film. The anisotropy and surface topography was measured by polarizing optical microscopy (POM) and profilometer. Using the red light which is insensitivity to the azo polymer film, the diffractive devices’focal spots were collected by CCD. By composite control of the optical power density, polarization direction and exposure time of the inscribing laser, a special phase-delay distribution graph which have different etching depth in different point can be achieved. Compared with the holographic interference method, the method is more flexible, undemanding for the experimental environment and any two-dimension distribution graph can be written in theory.5. The principle and realization of the azimuthally phase-delay generation of cylindrical vector beams (CVB) are presented by use of high-birefringence c-cut YV04crystal. The polarization was analyzed by a polarizer. The focus spot’s analytical solution near the objective focus has been calculated using vectorial diffraction theory, and its approximate distribution has been got by numerical integration. Compare to the ordinary CVB, all components of the focus shape are different, but smaller transversal size and flattop focus also exist. The focus shape is dependent on the objective numerical aperture (NA). The full width at half maximum’ radius of the azimuthally polarized beams’focus spot is equivalent to about60%of the diffraction limit. When the NA is big enough, the radius is smaller than the wavelength of1/2. The light bulbs whose density is0in the focus spot center and other forms of focal spot can be got by0-π phase-delay plate.