A polarization rotator and a polarization stabilizer. The polarization rotator includes a rib waveguide. The rib waveguide including: a slab portion; and a ridge portion, which is disposed along a surface of the slab portion. The slab portion has a first slab region whose width, as measured in a direction perpendicular to a guiding direction of the waveguide, increases from a first slab width to a second slab width along a first length, and the ridge portion has a first ridge region whose width, as measured in the same direction as the slab widths, decreases from a first ridge width to a second ridge width along the same first length; such that the rotator is configured to rotate the polarization of light during its transmission through the rib waveguide.