A compact and simple silicon nanowire based-polarization converter with ultra-high conversion efficient and broad bandwidth

Although the polarization converter utilizing silicon photonics technology has been reported several years ago, either the performance (conversion efficiency and operation window) or the manufacture is always limited by the cross-polarization coupling theory. We discovered that an asymmetric nanowire waveguide changing along the wave propagation direction produced a gradient effective mode index. A TE-to-TM polarization converter consisted of an asymmetric nanowire waveguide and a uniform nanowire waveguide constructed on the SOI platform was demonstrated. Gradient effective mode index effect and mode coupling theory promoted an ultra-high polarization conversion efficiency of 99.997% and broad wavelength operation window of 100 nm. Compact configuration presents high integration density, which benefits the on-chip mode multiplexing technology. Simple structure with moderate critical dimension facilitates the fabrication fast and cheap.