Free-space grating multi/demultiplexer and wavelength-router for densely spaced WDM networks

Densely spaced wavelength division multiplexed (WDM) networks using wavelength routing are considered to be potential candidates for the next generation wavelength routed optical networks. Very small channel spacing (⩽ 0.8 nm) in these networks will require high resolution demultiplexers transparent to modulation formats, combined with a high rejection of adjacent channels to ensure a low level of crosstalk. Whilst a low-loss and crosstalk free-space concave grating demultiplexer has been demonstrated, this article describes its transmission spectra using standard single mode optical fibre inputs and outputs and measured by three different high resolution techniques. The impact of grating aberrations and defocusing on demultiplexer transmission spectra are also discussed. We also demonstrate the wavelength channel drop in the double optical pass free-space grating router with single mode fibre input/outputs