| Grating has been studied and applied for many years. With the rapid development of optical communication technology and integrated optics,novel devices based on grating have caused increasing attention of domestic and foreign researchers. Sub-wavelength grating has many advantages, such as simple structure, great design flexibility, high efficiency, easy to integrate, and standard fabrication by micro-nano technology. So it is widely used in various optoelectronic devices including sensors, filters lasers and photodetectors. After proper designing for the structural parameters of sub-wavelength grating, the required reflectivity and bandwidth can be obtained, and the propagation direction of the beam can be changed, which is important to realize various functions.In this thesis, the sub-wavelength grating is the object to discuss.The theories and design methods are mainly studied. Two types of beam splitter with different structures and functions based on sub-wavelength gratings are completed. The detailed research work and innovative achievements are summarized as follows:1. The theoretical methods to analyze the diffraction properties of periodic sub-wavelength gratings are studied, including the Rigorous Coupled-Wave Analysis (RCWA) and the classical Modal Theory. Also,the numerical calculation method of non-periodic sub-wavelength gratings, which is Finite Element Method (FEM), is studied. The principle and solving process of FEM are introduced. And a simulation software based on FEM is described. Then characteristics of one-dimensional periodic sub-wavelength gratings are verified by the RCWA method, including broadband high reflectivity, high transmissivity and polarization-sensitivity.2. A polarization beam splitter with focusing ability based on two-layer one-dimensional sub-wavelength grating is presented. When the TE and TM mixed light with wavelength of 1550nm incidents, the device separates the two polarized beams, and each of them is focused.The simulation results show that the total transmittances under TE and TM polarized light incidence are 78.3% and 93%, respectively. The polarization extinction ratios are 13.8dB for TE light and 10.3dB for TM light.3. A polarization-independent power splitter based on 2D sub-wavelength high contrast grating (2D-HCG) is proposed. Properties of the splitter are numerically studied with the FEM. The simulation results show that, when the TE and TM mixed light incidents at wavelength of 1550nm, the total transmittance is 86.35%.The two beams converge into two focal spots with almost 1:1 power ratio. The focal length is 6.3?m, which is close to the designed 6.5?m. The device has an insertion loss of 3.65 dB, and the transmittance is greater than 85% within the range of 1500 nm to 1600 nm of wavelength.4. A 2D sub-wavelength grating based power splitter with the size of 250 × 250p?m~2 and the focal length of 200?m is designed. The layout of grating structure is drawn,and SOI based chip is etched. The experimental system for testing the splitting characteristics of grating power splitter is designed and built, and the experiment test is completed.The results show that the intensity ratio of the two output beams is 1: 0.9 at 1mm below the transmission surface, and the distance between the two spots is about 500?m. |
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