Phase-matched Second Harmonic Generation in Lithium Niobate Slow Light Photonic Crystal Slab Waveguides

Photonic crystals (PhCs) are promising platforms for integrated all-optical signal processing devices of classical and quantum nature. In particular, slow light modes in PhC waveguides can enable efficient and miniaturized nonlinear optical devices [1]. A suitable material for the fabrication of such devices is lithium niobate (LN), a dielectric with strong second order nonlinearity widely used for optical parametric processes. In recent years, nanostructuring LN slabs have been made possible [2], which allows for the fabrication of self-suspended PhC slabs. It has been demonstrated theoretically how second harmonic generation (SHG) is enhanced by slow light in a 2D lossless LN PhC [3], and experimentally for a gallium phosphide slow light PhC waveguide with a radiating generated second harmonic (SH) [4]. In this work, we design PhC waveguides in LN with a quasi-guided SH mode that is phase-matched to a slow low dispersion fundamental harmonic (FH) mode.