NONCRITICAL PHASE MATCHING FOR GUIDED-WAVE FREQUENCY-CONVERSION

Inhomogeneities in waveguide dimensions are a serious problem for guided-wave frequency conversion devices. We discuss waveguide designs that make the phase matching "noncritical" with respect to small changes in dimensions. Application of noncritical phase matching results in larger fabrication tolerances, facilitating the practical realization of nonlinear devices with long interaction lengths. We experimentally demonstrate the existence of a noncritical thickness in a lithium niobate waveguide, and analyze the dimensional tolerances for second-harmonic generation in a polymer waveguide.