Polarization-free second-order nonlinear frequency conversion using the optical superlattice

We propose a universal and practical scheme to realize polarization-free second-order nonlinear frequency-conversion processes, including sum-frequency generation, difference-frequency generation, and optical parametric amplification. This scheme is based on the optical superlattice with a noncritical phase-matching condition, which is suitable for optical integration. A chirped dual-period structure is proposed to ensure the efficiency and stability of the conversions.