Novel High Contrast Sub-wavelength Gratings In Optical Communication System

Sub-wavelength grating has the unique optical properties that the traditional grating does not have owing to its sub-wavelength structure size.Its grating period is between the wavelength in the grating and the wavelength around the grating.Meanwhile,its miniaturized structure can be used in the field of integrated optics.So with the rapid development of micro-and nano-technology,sub-wavelength grating as the important micro optical device,has applied widely in many fields,such as holography,spectroscopy,optical communication and information processing.In optical communication system,the High Contrast Sub-wavelength Grating(HCG)is the sub-wavelength grating whose grating bars made by high refractive index material are completely surrounded by low refractive index material.HCG can be made into high performance mirrors or lenses,polarizers,deflectors,beam splitters,filters and so on by changing the grating parameters.So,HCG has become a hot topic in optical communication system.This thesis mainly focuses on the High Contrast Sub-wavelength Grating which applied in optical communication systems and studies its unique performances theoretically and experimentally.The main research content and innovation in this thesis are as follows:1.Three research methods of grating are studied,namely,Rigorous Coupled Wave Analysis(RCWA),Model Method and Finite Element Method(FEM).The RCWA method can clearly analyze the diffraction characteristics of the surface of the HCG when the HCG is transmitted by an incident wave,and the Model Method is more suitable to analyze the interaction of the grating mode in the interior of the HCG.In this paper,the study is mainly about the transmission coefficient and the transmission phase,the reflection coefficient and the reflection phase,reflectivity after the light passing through the HCG,so the RCWA method is more suitable.2.The characteristics of HCG in optical communication system are discussed,and the applications of HCG in optical communication system are summarized.The influence of HCG's characteristics varying with its parameters is studied using RCWA method through mathematical tool MATLAB.3.The designing method of the structure for high performance single-layer silicon HCG convergent mirror under TM-polarized normal incident wave is researched and completed based on the high reflectivity and the principle of wave front phase control of HCG.The thickness of the designed HCG mirror is 1.2?m,and the total width is 36?m.The designed HCG mirror is calculated by FEM.The reflectivity is 74.1%,the focal length is 7?m and the full-width-half-maximum(FWHM)is 0.65?m at a wavelength of 1.55?m.It has achieved good convergent reflection characteristic.4.The structural design method of HCG convergent lens which is a single silicon layer HCG with TE-polarized normal incident wave of 1.55?m is mainly researched.To solve the problem of "phase discontinuity" which is unwanted in studying the phase of the TE-polarized converging lens,a new grating parameter selection algorithm is proposed.This parameter selection algorithm can not only be used to design high performance converging mirrors and converging lenses,but also be used to design deflectors.5.A new structure of double thicknesses HCG convergent lens is proposed.The double thickness HCG convergent lens under TE-polarized normal incident wave is completed.The structure of this convergent lens has one-layer silicon,the thicknesses are 1.3?m and 1.2?m,the total width is 26?m.The designed double thickness HCG lens convergent lens is studied by FEM.The total transmissivity is 72%,the focal length is 7.2?m and the full-width-half-maximum(FWHM)at focal plane is 0.8?m at the normal incident wave of 1.55?m.It has achieved good convergent transmission characteristic.6.On the basis of the designed double thickness HCG converging lens,a new type of double thickness HCG beam splitter is completed.At the same time,the parameters of the designed HCG beam splitter are calculated by the mentioned parameter selected algorithm.The structure of the designed double thickness HCG beam splitter is calculated by FEM.The total transmissivity can reach 77.5%.The power ratio 1:1 can be realized.7.The HCG convergent mirror with TM-polarized normal incident wave is completed.The test system of the completed HCG converging mirror is designed and set up.The performance of the HCG converging lens is made by the experiment.The focal length of the experiment is 11.86mm,and the total reflectivity can up to 67.7%at 1.55?m.