Near-diffraction-limited performance at 1.5 mu m of a free-space conca
ve ruled grating demultiplexer for densely-spaced wavelength routed ne
tworks is reported. Over the wavelength range of 16nm (40 channels) an
d channel spacing of 0.4 nm, the fibre-to-fibre loss was 6-9dB and cha
nnel crosstalk was better than 25dB.