Abstract: A configuration for multiplexing and/or demultiplexing the signals of at least two optical wavelength channels, is described. Provided in this case is a grating device having an optical grating, a first optical free beam region and a second optical free beam region. Accordingly, radiation is coupled into and out of the first free beam region via a coupling device which effects a flattening and/or widening of the field distribution of the light coupled in or out, at least in the plane of the first free beam region. This permits a transmission characteristic of the configuration to be flattened.