Submillimeter wave surface-emitting difference frequency generation in periodically poled lithium niobate waveguide

The submillimeter wave difference frequency generation (DFG) in periodically poled lithium niobate (LiNbO/sub 3/) (PPLN) waveguide structure is considered theoretically. It is shown that the PPLN waveguide is capable of emitting difference frequency radiation in direction normal to the surface of a waveguide if the poling period is equal to L=/spl lambda//n/sub g/ (/spl lambda/ is a wavelength of submillimeter radiation and n/sub g/ is a mean refractive index of the optical group velocity). In contrast to the optical waves, the PPLN waveguide with such period can be easily fabricated for the submillimeter wave DFG.