Uniaxially patterned (UAP) dielectric layers have an optical anisotropy that can be dynamically controlled. In a three-layer optical waveguide structure, the pattern can be included in the core or in a cladding layer. The pattern influences the polarization properties of radiation propagating in the structure. Predicated on the effect are devices such as a polarization-insensitive amplifier, a polarizer, an optically controlled polarization switch, and an optically controlled modal coupler.