Highly efficient silicon optical polarization rotators based on mode order conversions

We design and demonstrate the novel silicon optical polarization rotators (PRs) based on the TM(0)-TE(n)-TE(0) mode conversions inside the waveguide. The TM(0)-TE(n) mode converters are realized by the mode hybridization of the tapered rib waveguides. The TE(n)-TE(0) mode converters based on the beam shaping method are followed to complete the PRs function. By using the TE(1), TE(2), and TE(3) mode as the transitional mode, the fabricated PRs show the insert losses of less than 0.4, 0.5, and 1 dB, respectively. The corresponding polarization extinction ratios of larger than 21, 18, and 23 dB, over a wavelength range of 100 nm.