Simultaneously phase-matched second- and third-harmonic generation from 1.55 μm radiation in annealed proton-exchanged periodically poled lithium niobate waveguides

Third-harmonic generation (THG) in the cw regime from C-band radiation was achieved in annealed protonexchanged periodically poled lithium niobate (PPLN) waveguides. By suitable design of fabrication parameters and operating conditions, quasi-phase-matching (QPM) is obtained simultaneously for the second-harmonic generation process (ω→-2ω, first-order QPM) and for the sum-frequency-generation process (ω +2ω→-3ω, third-order QPM), which provides the third harmonic of the pump field. The high overlap between the field profiles of the interacting modes-TM00 at ω and TM10 at 2 ω and 3 ω-results in what is believed to be the highest ever reported normalized conversion efficiency for THG from telecommunication wavelengths, equal to 0.72% W-2 cm -4. © 2006 Optical Society of America.