We constructed rib waveguides from GaP material using an inductively coupled plasma reactive ion etching technique based on Ar/ Cl2 gas application. We obtained a waveguide with a rib height of 200 μm. Terahertz-wave generation from the GaP-crystal rib waveguides was demonstrated via collinear phase-matched difference-frequency mixing of near-infrared light. The terahertz output peak corresponding to the fundamental modes appeared around 0.75 THz for a 1-mm-wide rib waveguide. The position of the fundamental mode shifted to 1.32 THz for a 200-μm -wide waveguide, which is attributable to the two-dimensional confinement of the terahertz waves in the waveguide. The conversion efficiency was enhanced in the rib waveguide compared to that in both slab waveguides and bulk GaP crystals.
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