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Birefringence phase-matched direct Third-Harmonic Generation in a ridge optical waveguide based on KTiOPO4 single crystal

Birefringence phase-matched Third-Harmonic Generation at 1594 nm is performed for the first time in a KTiOPO4 single crystal micrometric ridge waveguide. The energy conversion efficiency reaches 3.4% for a pump energy as low as 2 µJ over a pulse duration of 15 ps at a repetition rate of 10 Hz. Strong agreements between theory and experiments for both phase-matching and conversion efficiency is obtained, which let envision future Triple Photons Generation quantum experiments.