Modeling Silicon-Based Periodic Waveguides for Optical Interconnects
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Modeling Silicon-Based Periodic Waveguides for Optical Interconnects Meng-Mu Shih University of Florida, Gainesville, FL 32611, U.S.A.
ABSTRACT To assist the precision and stability of wavelength at 1550 nm and 1300 nm in planar optical waveguides, hybrid semiconductor-metal corrugated gratings with nanometer period are integrated into silicon-based optical interconnects. This work utilizes multi-parametric optical waveguide models to compute the mode-coupling coefficients in the silicon photonic devices. For such a semiconductor-metal hybrid structure, a proper photonic technique needs to be utilized to solve this computational complexity. The optical method and the photonic method are used to compute coupling coefficients. Both methods have close numerical values shown in figures. Numerical results demonstrate how the normalized corrugation amplitudes of metal gratings can affect the coupling coefficients. Further physical interpretation and discussion can support and explain the above results. The modeling results can help engineers decide the values of parameters used in the design and fabrication of optical waveguides. INTRODUCTION To enhance the performance of electronic products, optical interconnects have been considered to be an alternative way to transmit data or process signals with less power consumption and less heat generation. Silicon is abundant on earth and silicon-based fabrication technique has been widely used in electronics industry. Utilizing silicon material in photonic devices possibly can not only reduce cost but improve the performance. Optical waveguides are the common structures in photonic devices. In a planar waveguide, there is no optical feedback mechanism. Gallium-arsenide-based waveguides with built-in metal gratings having distributed feedback (DFB) mechanism were discussed [1]. In a waveguide with the corrugated gratings adjacent to the semiconductor structure, the DFB can improve the performance of applications by stabilizing the output wavelength for optical communications [2]. By using the shiny metal as the grating material, such gratings can provide the following advantages [3] such as high diffraction efficiency and mode confinement in the waveguides. Figure 1 schematically shows the cross-section view of a waveguide structure for a silicon-based DFB semiconductor-metal waveguide, operating at the wavelengths of 1550 nm and 1300 nm in the near-infrared range. The frequencies corresponding to these two wavelengths are about190 and 230 Tera-Hertz (THz), respectively. These two wavelengths are popular for many optical components and communications. Such a four–layer waveguide structure is composed of three semiconductor layers and one metallic layer. The materials of silicon (Si), silicon dioxide (SiO 2) are chosen [4] in the semiconductor layers and gold (Au) in the shiny metallic layer. These layers have the following optical parameters of refractive indices at 1550 nm: active layer or called active region (na = 3.48 for Si [5]), buffer layer (nb = 1.44 for SiO2 [5]), claddi
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