Multimode interference (MMI) couplers, based on the self-imaging effect (SIE), are accepted popularly in integrated
optics. According to the importance of MMI devices, in this paper, we present a novel method to design and fabricate
MMI couplers. A technology of maskless lithography to make MMI couplers based on a smart digital micro-mirror
device (DMD) system is proposed. A 1×4 MMI device is designed as an example, which shows the present method is
efficient and cost-effective.