Research Of Subwavelength Focusing Effect By A Mircro/Nano Structure

Due to the diffraction limit of traditional optics, sub-wavelength focusing spot can't be obtained in far field. The ability to focus light beams with sub-wavelength resolution is essential to a wide range of applications including optical disk storage, semiconductor lithography, confocal microscopy, optical trapping, and laser surgery.According to the super-oscillation theory and utilizing the diffraction property of the output light from micro/nano aperture, a new scheme based on a micro/nano structure to focus optical beams with sub-wavelength resolution in the far field is proposed. Three kinds of micro/nano structures including micro/nano fiber array, micro/nano glass rings and micro/nano germanium rings are designed. By using the three-dimensional Finite Difference Beam Propagation Method (FD-BPM), we calculated the focusing effect of those structures and in further investigated the influences of properties of micro/nano structure and input optical field on focusing effect. We made the designed micro/nano glass rings and micro/nano germanium rings, constructed experimental systems and completed the measurement of optical spots. In the end, we briefly analyzed the application of this sub-wavelength focusing spot in confocal super-resolution microscopy.In the beginning of the thesis, the meaning and the development situation of the sub-wavelength focusing is shortly presented. Then we compare the principles, focusing effects and limitations of several important focusing methods.The basic thinking of super-oscillation is firstly presented in second chapter. Based on super-oscillation theory three kinds of micro/nano structres are designed, including micro/nano fiber array, micro/nano glass rings and micro/nano germanium rings. And using the three-dimensional finite-difference beam-propagation method, we give the focusing effects of the three structures.In third chapter, taking example of micro/nano fiber arry, we analyzed the influences of the properties of micro/nano structures and input optical field on focusing effects.In the forth chapter, utilizing focus ion beam and hot stretching technologies, we made the designed micro/nano glass rings and micro/nano germanium rings. Based on microscopy objective and SNOM probe we constructed experimental systems and completed the measurement of optical spots. In the end, we shortly discussed the application of this sub-wavelength focusing spot in confocal super-resolution microscopy.At the end of the thesis, the conclusion and future research direction are given.