In this paper, we present a new design approach for WDM optical interconnects that reduces both switching and wavelength conversion complexity. The proposed design approach employs wavelength conversion strictly between two pre-specified wavelengths, independent of the total number of wavelengths in the network, thus eliminating the need for widerange converters. We investigate both single-stage and multi-stage interconnects. For the single-stage design, we present a full-connectivity interconnect with a smaller number of switching elements compared to most existing designs. For multi-stage interconnects, we consider 3-stage designs, and present two design methods and investigate optimal interconnects for each of the two methods. Finally, we present a cost model to analyze the hardware complexity of the different designs. Cost analysis shows that, the proposed designs can achieve a significant cost saving compared to most designs. In particular, under various conditions, the proposed designs can achieve up to 40% reduction in cost compared to best known 3-stage designs.