Designing And Optimization Of Silicon Based Polarization Controller

For many applications of silicon photonics, such as fiber communication, the light from optical fibers usually has a random polarization. However, the silicon waveguide and other silicon devices generally have a considerable birefringence. Consequently, the signal will degrade seriously after it goes through a polarization-sensitive photonics integrated circuits, which limited the application area of silicon PICs. Therefore, eliminating the polarization-sensitivity is extremely important for the commercialization of silicon PICs. As the key component for solving such problem, the polarization converters has attracted considerable attention in recent years. The polarization converters are used to convert the input polarization states into its orthogonal ones. They have many applications, such as polarization diversity, integrated quantum information and polarization division multiplexing.The purpose of our work is to design and optimize the polarization converters base on silicon-on-insulator wafer. It mainly include two parts, the first part is the design of fiber-waveguide coupling devices such as grating coupler s and adiabatic tapers, the second part is the design of two different kinds of polarization rotators. Besides, we use particle swarm optimization algorithm in this work to optimize geometric parameters of the devices, a nd we have got excellent results by this optimization method. The main content of this paper incl udes:1. The comprehensively optimization of the geometric parameters of a double-etched non-uniform grating coupler by PSO algorithm. The optimized grating coupler is totally CMOS compatible and can be fabricated easily. It has a coupling efficiency of 75.5%(insertion loss of 1.2d B) at wavelength of 1550 nm, 1d B-bandwidth covers whole C band.2. We propose a Bezier curve type adiabatic taper to connect two waveguide with widths of 12μm and 0.5μm. The length of proposed taper is only 50 μm, and the transmittances are higher than 98% during the wavelength range from 1540 nm to 1600 nm.3. A novel ultra-compact polarization rotator based on surface plasmon polaritons waveguide is proposed. Total footprint of the proposed device is only 0.44um×2.56 um. Numerical stimulation by 3D-FDTD shows that the proposed PR has a broad band(1.4μm~1.7μm) with extinction ratio >10d B. The insertion loss is lower than 0.75 d B in whole C band, which is the smallest IL in all SPP-PR to the best of our knowledge.4. We optimize a mode-evolution-based polarization rotator. The optimized PR have an extremely broad bandwidth and low insertion loss. During wavelength range of 1400nm~1700nm, the extinct ratio higher than 17 d B and insertion loss lower than 0.1d B. At wavelength of 1550 nm, ER is 26.3d B and IL as small as 0.006 d B.