We design an AlGaAs-based terahertz photonic crystal waveguide (PCW) to achieve terahertz-wave difference frequency generation (DFG) from near-infrared light sources. The PCW structure provides a tight confinement of terahertz-wave field, resulting in a good mode field overlap of three waves. The unique phase matching condition between two pump waves and terahertz Bloch wave can be satisfied through choosing appropriate waveguide parameters and pump wavelengths. With the coupled-mode equations derived from modal theory for describing the light propagation, we simulate the continuous terahertz DFG process, and a high power-normalized conversion efficiency of 0.7632 × 10<sup>-4</sup> W<sup>-1</sup> for 3 THz generation is obtained.
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