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We present measurement results of an ultracompact four-channel silicon-on-insulator planar concave grating demultiplexer fabricated in a complimentary metal–oxide–semiconductor line using deep-ultraviolet lithography. The demultiplexer has four output channels separated by 20 nm and a footprint of only 280 m150 m. The crosstalk is better than 25 dB and the on-chip loss is drastically reduced down to 1.9 dB by replacing each facet by a second-order Bragg reflector.