Regarding the importance of bandwidth and capacity expansion in communication systems, a novel mode division (de)multiplexer based on subwavelength grating (SWG) is proposed. SWG-based devices could have smaller sizes, be much more fabrication-tolerant, and have much wider bandwidths due to the reduced confinement of the field and dispersion. It is also feasible to reduce the loss of a SWG-based device by tuning the duty cycle of the grating. Owing to these properties of SWGs, we have designed a compact fabrication-tolerant two-mode division (de)multiplexer. A flat-top transmission of >0.89 (loss <0.5 dB) is obtained over 65 nm from 1500 to 1565 nm, completely covering the entire C-band used for dense wavelength division multiplexing. Moreover, the cross-talk is <-10 dB for a broad bandwidth of ∼120 nm over which the loss of the complete device including both multiplexer and demultiplexer is <1 dB. Therefore, the proposed device is promising for high-capacity optical communications in both conventional and entirely SWG-based silicon photonic circuits.