Angle tunable frequency conversion in form-birefringent nonlinear metamaterials.

Phase matching (PM) of nonlinear optical interactions is central for obtaining efficient frequency conversion. Birefringent PM, which is highly useful in anisotropic nonlinear crystals, is limited by intrinsic bulk properties. However, application of this method can extend beyond natural constraints through form-birefringence in layered metamaterials. Here, we theoretically and numerically analyze angle-tuned form-birefringent PM in an infinite periodic laminar metamaterial, consisting of GaAs and SiN. We demonstrate configurations for efficient second harmonic generation of near-infrared radiation and difference-frequency-generation of mid-infrared light. An angular tunability of over an octave for mid-infrared generation in the range of ∼3.3 - 6.7 is demonstrated. These findings motivate the construction of bulk form-birefringent metamaterials as a new platform for nonlinear optics.