A simple scheme to generate optical quadrature amplitude modulation (QAM) signals is proposed based on different types of delay interferometers (DIs). The simulated results show that 16QAM, 64QAM and 256 QAM optical signals can be generated by 2×2, 3×3 and 4×4 DI, respectively, and the outputs of the proposed scheme are similar to those of the conventional schemes. The operation principle is discussed and the transmission properties of the square 16QAM as well as 64QAM signals are analyzed and compared with common approach.