Terahertz (THz) generation was demonstrated from GaP rod-type waveguides via difference-frequency-mixing of near-infrared light using a collinear phase-matching condition. THz output peaks were observed, and appeared at frequencies corresponding to the fundamental and high-order waveguide modes. Interestingly, the position of the fundamental mode shifted to a higher frequency for a smaller waveguide cross-section, which is attributed to the waveguide confinement of the THz wave. The conversion efficiency was enhanced in the waveguide with a cross section of 200 μm × 160 μm as compared to that in bulk GaP crystals.
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