摘要： We present a theoretical research concerning simultaneous generation of two terahertz (THz) waves with bulk LiNbO3 and four THz waves with periodically poled LiNbO3 (PPLN) by coupled optical parametric generation (COPG). First, we investigate collinear phase matching of COPG generating two orthogonally polarized THz waves with two types of phase matching of o = e ? e and o = e ? o with bulk LiNbO3. The two orthogonally polarized THz waves are generated from stimulated polariton scattering (SPS) with A1 and E symmetric transverse optical (TO) modes in bulk LiNbO3, respectively. Then, we ?nd that perturbations of phase mismatch for o = e ? e and o = e ? o can be compensated by a same grating vector of PPLN. As a result, four THz waves are simultaneously generated with a PPLN crystal and a pump laser. We calculate third-order nonlinear optical coef?cients of o = e ? o generating THz waves from E symmetric TO modes. The intensities of four THz waves are calculated by solving coupled-wave equations. The calculation results demonstrate that four THz waves with high intensities can be simultaneously realized by COPG with existing laser technology and crystal fabrication technology.