Ultra-compact polarization rotator based on mode coupling in a groove-like waveguide, assisted by subwavelength grating

Abstract

A novel (to the best of our knowledge) scheme of an ultra-compact polarization rotator (PR) is based on an optical-axis-rotated section of a groove-like waveguide with a subwavelength grating (SWG) structure, which is used to replace one of the silicon strip waveguides in the polarization conversion section. In the proposed scheme, the mode coupling occurs, and the mode conversions between fundamental transverse magnetic mode ( T M 0 ) and fundamental transverse electric mode ( T E 0 ) are realized. At the operating wavelength of 1.55 µm, the simulated extinction ratio (ER) of ∼ 41 d B , insertion loss (IL) < 1 d B , and reflection loss (RL) < − 22 d B for the T M 0 - t o - T E 0 conversion with a total conversion length of 5.4 µm have been obtained. The simulated transmission spectra also show a relatively broad bandwidth of 53 nm (41 nm) for the T M 0 - t o - T E 0 ( T E 0 - t o - T M 0 ) conversion to keep the E R > --> 25 d B ; as well as a high polarization conversion ratio of 99.95% (99.31%) for the T M 0 - t o - T E 0 ( T E 0 - t o - T M 0 ) process at 1.55 µm. The presence of SWG greatly enhances the device performance, and the tolerance to fabrication uncertainties has also been investigated.