Research On Subwavelength Gratings And Its Applications

This thesis mainly researches subwavelength grating and analyzes the diffractioncharacteristics and applications of it. The grating period of the subwavelength grating is lessthan the wavelength of incident light. As this reason, the subwavelength grating has onlyzero-order diffraction wave and higher order diffraction waves are evanescent wave. We canuse this unique diffraction properties of subwavelength grating to realize many opticalfunctions which can not be achieved by many traditional optical devices.In this thesis, we propose a novel structure subwavelength grating-the subwavelengthhigh refractive index contrast grating (HRCG). We design the HRCG as a polarizing beamsplitter, quarter wave plate and a hollow-core waveguide by optimizing its structuralparameters. The main research work is summarized as follows:(1) The diffraction properties of the subwavelength grating is introduced. The mainapplication of subwavelength grating in recent years is illustrated.(2) The theory researches methods of grating is introduced. It has been pointed out thatthe subwavelength grating needs vector diffraction theory to analyze. This paper uses therigorous coupled-wave theory and effective medium theory to design subwavelength grating.We elaborate on the solving principles of these two theories.(3) A novel subwavelength grating-high refractive index contrast grating is proposed.We use the rigorous coupled-wave theory to analyze its diffraction orders. Through theoptimization of structural parameters, we design the HRCG as a polarizing beam splitter.This polarizing beam splitter has a very high extinction ratio,25583.1and112896.8,respectively for TE and TM polarized light when incident light wavelength is1550nm.(4) Second-order approximation of subwavelength grating effective medium theory isintroduced. We use this theory to design HRCG as quarter wave plate. This quarter waveplate has a good phase delay characteristics for the TE and TM polarized light when theincident light wavelength is in the range of1350~1750nm.(5) The multi-layer HRCG structure is introduced and designed as a broadband filter. Itis pointed out that the diffraction field of the multi-layer HRCG structure broadband filter isinfluenced by the interference effect of the multi-layer film structure. We can use this featureto design and improve the filtering performance of this filter. We discussed the influence of the number of layers and grating the refractive index for the broadband filter filteringperformance. We designed a multi-layer HRCG structure broadband filter of which thecenter wavelength is1550nm and the reflection spectrum width is843nm.(6) The development of hollow-core waveguide is introduced. It has been pointed outthat the large loss is a common drawback for all current hollow-core waveguides. The HRCGhas a high reflectivity and a broad reflection spectrum. We designed it as a hollow-corewaveguide. This hollow-core waveguide has lots of advantages like polarization selectivity,low loss for low order modes, low loss in a wide spectral range. On this basis, we alsodesigned the2D HRCG hollow-core waveguide. It can be well to restrict the light to spreadin the waveguide.