A multi-channel optical switching system particularly usable as a programmable optical add/drop multiplexer in a multi-wavelength communication system. The switching system uses a grating operating at Littrow that separates a multi-channel optical signal into a plurality of optical channels, and combines a plurality of optical channels into a multi-channel optical signal. The system also uses a plurality of optical ports optically coupled to the grating and a selecting device to select which optical channel is directed to which of the optical ports.