Transmission passband, optical crosstalk and cascadability of free-space concave grating demultiplexer for dense WDM networks

We describe the performance of a 100 channel free-space concave grating dem ultiplexer with 1 dB transmission passband of +/-7 GHz (FWHM 14-22 GHz). Th e influence of optical aberrations and defocusing on the transmission spect rum is demonstrated. Crosstalk between neighbouring channels separated by > 0.3 nm is lower than -25 dB and no penalty due to crosstalk is observed usi ng 2.6 Gbit/s directly modulated DFB lasers. Penalty-free transmission thro ugh a cascade of 30 demultiplexers is demonstrated in an optical fibre reci rculating loop experiment, and the permitted tolerances on the laser freque ncy misalignments for a larger number of cascaded demultiplexers are invest igated.