We report a high-density wavelength division demultiplexer (Demux) capable of demultiplexing a 32-channel 100-GHz-spaced wavelength, with a working wavelength range of operation from 1541.37 to 1565.47 nm. The design, packaging, and performance of the Demux using the 22nd diffraction order of an echelle grating is described. The typical insertion loss of the device is -3.0±0.2 dB, the cross talk between adjacent channels for all 32 channels is about -30 dB, and the average 1-dB optical passband is 0.256 nm. We found the experimental measurement result of the 1-dB passband to be in good agreement with the theoretical 1-dB passband as calculated. The device has singlemode fiber in and multimode fiber out, and thus can bridge the telecommunication backbone and local area networks.