Design Of High-efficiency Mode Converter For Silicom Slot Waveguides

Silicon slot waveguide can effectively reduce the effective mode area of waveguide, thus enhancing its nonlinear effects. In order to ensure the efficient nonlinear effects to occur, the incident light from fiber needs to be coupled into the slot waveguide as much as possible. However, mode field shape and size between the fiber and the slot waveguide don’t match, resulting large butt coupling loss. Therefore it needs to design a mode converter of high coupling efficiency and broad band.The mode converter designed here between the optical fiber and the silicon slot waveguide is realized by two steps:firstly, realizing a mode converter between fiber and silicon strip waveguide, secondly, designing a mode converter between silicon strip waveguide and silicon slot waveguide.The article first reviews the basic principles of optical waveguide and numerical methods to simulate optical waveguide. Then, we design a fiber-to-silicon waveguide inverse taper mode converter. When the tip width and height equal 0.1 μm,0.25 μm, respectively. TE mode has a total loss of 0.483 dB, and for TM mode it’s 0.653 dB. And when the tip width is less than 50 nm, polarization independence is achieved with loss of TE/TM approximately 0.2 dB. After that, the length of the taper is optimized and reduced to 234 μm. Then, by reducing the height of the waveguide or moving the tip to the side. Polarization independence is less than 0.11 dB, while the total loss of TE/TM approximately equals to 0.4 dB.Later based on the characteristics of slot waveguide mode, we finish the design of a strip-to-slot waveguide mode converter with a converting length of 20 μm and the minimum structure size more than 100 nm, achieving a conversion efficiency of 99.2%, and a bandwidth of 200 nm with conversion efficiency greater than 95%. After further optimization,3 μm of the conversion length is reduced with the bandwidth increased 100 nm, exhibiting an excellent property.