Efficient difference-frequency mixing of diode lasers in lithium niobate channel waveguides

Reported are design, fabrication recipes, and performance of channel wavegu ides for mid-infrared difference-frequency mixing of diode lasers. The wave guides were formed by annealed proton exchange in periodically poled lithiu m niobate, and included a mode filter, a taper, and a mixing channel. Two d esigns of the mode filter and taper were investigated, one involving period ic segmentation. Device efficiencies of 1.4 % W-1 - 4.0 % W-1 were achieved for difference-frequency generation in the 2.8-3.6 mu m wavelength region using near-infrared diode lasers as pump sources. Up to 136 mu W output pow er was obtained at 2.8 mu m with 198mW total launched power. Measured conve rsion efficiencies were typically four times lower than predicted. Departur e of the taper behavior from adiabatic contributed to this discrepancy.