A widely tunable THz wave has been parametrically generated and reported recently by us utilizing aLiNbO3crystal with a monolithic grating coupler under a noncollinear phase matching condition. However, the output direction of the THz wave is strongly dependent on the generated frequency due to the nature of noncollinear phase matching, as well as the grating coupler. In this letter, a novel method for THz coupling is proposed using a low dispersion prism to eliminate almost completely the THz beam deflection for the entire tuning range. The unidirectional THz wave radiation was confirmed theoretically and experimentally for the range of 1–2 THz. ©1997 American Institute of Physics.