Abstract:For multimode optical waveguides, the mode transmission becomes especially complex. In this work, the crossing structure consisting of two multimode waveguides was analyzed by using beam propagation method (BPM). From the analysis of the modes of Exp,q, it was found that the transmission modes were almost same for the same subindex p with the increasing subindex q. And the optical power crosstalk becomes strong between the two crossing waveguides for smaller crossing angles.