We propose a new approach for the design of phased array (PHASAR) demultiplexers. This approach is based on cascading multimode interference (MMI) PHASAR structures with different frequency responses to obtain an optimized performance. We show that with this approach, we can improve the uniformity of the overall demultiplexer (DMUX), especially when a large number of output ports is required. The design of a 64-output DMUX with only 0.2-dB uniformity is thus demonstrated compared to a 7-dB uniformity of a two-cascaded eight-channel demultiplexer, also shown in this work. This approach allows the designer to optimize the structure design, considering both the insertion loss and the uniformity. © 2004 Society of Photo-Optical Instrumentation Engineers.