Light propagating in an out-of-plane curvilinear waveguide acquires a Berry's phase, which rotates optical polarization. The effect is promising for realizing waveguide polarization controllers. In high index contrast platforms, such as silicon-on-insulator, however, small waveguide cross-sectional asymmetries reduce the amount of polarization rotation. To overcome this, we present a method based on the periodic spatial modulation of Berry's phase. Ninety degree polarization rotation is achieved, even in the presence of waveguide asymmetry. Using a numerical model based on Jones calculus, we demonstrate the approach with 303×300 nm2 asymmetric silicon waveguides. We convert polarization from transverse electric to transverse magnetic with a polarization extinction ratio (PER) greater than 20 dB PER over a 100 nm bandwidth in a 110×240 μm2footprint.