The multiplexer/demultiplexer has a planar reflector, a planar first filter element and a planar second filter element offset from the first filter element in a first direction to receive light reflected and transmitted from a first location on the first filter element. The first and second filter elements have orthogonal surface normals. The reflector is parallel to the second filter element and is offset therefrom in a second direction, orthogonal to first direction, to receive light reflected and transmitted from a second location, offset from the first location in the second direction, on the first filter element. The first and second filter elements each transmit and reflect light in non-overlapping wavelength ranges, and one of them has a band-pass or band-stop transmission characteristic.