Optical sum-frequency generation has been observed in channel waveguides produced by proton exchange in LiNbO3 as well as LiTaO3 substrates. Simultaneously coupling 5-mW cw from a Nd:YAG laser operating at 1.32 µm and 8-mW cw from a second Nd:YAG laser operating at 1.06 µm into a channel waveguide formed in a Z-cut LiNbO3 substrate resulted in sum-frequency generation in the yellow. The sum-frequency output emerges from the waveguide as Cherenkov radiation. Second harmonic radiation from both inputs also emerges as Cherenkov radiation but is spatially separated from the sum-frequency output. The power produced at the sum frequency as well as the second harmonic at 1.32 µm is approximately equal to 0.25 µW resulting in a combined red-yellow output of 0.5 µW. Similarly, coupling 1-mW cw at 0.840 µm from a laser diode in conjunction with the 1.06-µm input into the same waveguide gives sum-frequency generation in the blue. Conversion efficiency depends on modal content, wavelength, and scattering. A guide which supports one or two modes at 1.32 µm is more efficient in both sum frequency and second harmonic generation if simultaneously pumped at 1.06 µm than the same guide pumped with the combined input at 0.84 and 106 µm.
