A single-stage 1×5 grating-assisted wavelength division multiplexer is provided. A grating-assisted asymmetric Mach-Zehnder interferometer, a plurality of grating-assisted cross-state directional couplers and a plurality of novel side-band eliminators are combined to form the multiplexer. Only general gratings are required, not Bragg grating, for 5-channel wavelength division multiplexing in a single stage. A nearly ideal square-like band-pass filtering passband is obtained. The present disclosure can be used as a core device in IC-to-IC optical interconnects for multiplexing and demultiplexing of an optical transceiver. The present disclosure has a small size and good performance.